Big Ideas Simply Explained - The Astronomy Book

["NEW WINDOWS ON THE UNIVERSE 249 CM\/SM CSM\/LM docking CSM and LM separation, separation LM jettison Touchdown CSM\/ LM undock Saturn V CSM reoriented LM descent launch to dock with LM orbit insertion Apollo 11\u2019s command and service module docked LM = Lunar module Outbound with the lunar module in orbit before heading for the moon. CM = Command module Inbound Before touchdown, the service module was jettisoned, and SM = Service module only the command module returned to Earth. CSM = Command service module scientific priorities changed, Apollo contracts also nurtured today\u2019s Silicon Valley. But perhaps politicians worried about costs, nascent industries, such as Apollo\u2019s real legacy is the idea and human space travel has not computing and semiconductors. of Earth as a fragile oasis of life ventured farther than Earth\u2019s orbit. Several employees of the California- in space. Photos taken from orbit, based Fairchild Semiconductors such as the \u201cBlue Marble\u201d and For many, the decision to end went on to found new companies, \u201cEarthrise\u201d (p.247), fed into a manned moon missions was a including Intel, a technology giant. growing awareness of planet wasted opportunity, caused by a The Santa Clara area where these Earth as a single entity, and the lack of imagination and leadership. firms were based has become need for careful stewardship. \u25a0 However, the end of the acute Cold War competition that gave rise to the Apollo program heralded a new era of international cooperation for NASA, with Skylab, Mir, and the International Space Station. Gene Cernan, the last man on the moon, predicted that it could be another 100 years before humankind appreciates the true significance of the Apollo missions. One result could be that it may have made the US smarter\u2014the intake for doctoral degrees at American universities tripled during the 1960s, particularly in the field of physics. On the final three Apollo missions, astronauts explored the surface of the moon on lunar rovers. The rovers were abandoned and can still be seen where they were left behind.","250 AFTRNHODEMPDLUAASDNTIESTKSOFFOGRAMSED THE NEBULAR HYPOTHESIS IN CONTEXT F or centuries, astronomers A version of this hypothesis have proposed various was put forward by Frenchman KEY ASTRONOMER models to explain how the Pierre-Simon Laplace in 1796. Viktor Safronov (1917\u20131999) sun and planets formed. During the 18th and 19th centuries, the In the late 1960s, Viktor Safronov BEFORE nebular hypothesis came to was working in Moscow on how 1755 German philosopher prominence. This proposed that the planets could form in a nebula. He Immanuel Kant argues that the solar system emerged from a giant wrote an important paper in 1969, solar system formed out of a cloud of gas and dust that collapsed which was unknown outside the large gas cloud that collapsed. and started rotating. Most of the Soviet Union until an English version material collected in the center, was published in 1972. Safronov\u2019s 1796 Pierre-Simon Laplace forming the sun, while the rest theory, which today is known develops a model of solar flattened into a spinning disk of as the solar nebular disk model system formation that is material from which the planets (SNDM), was essentially a modified, similar to Kant\u2019s. and smaller objects condensed. mathematically more fully formed version of the nebular hypothesis. 1905 The American geologist Thomas Chrowder Chamberlin In the disk of material In these collisions, first proposes that planets orbiting the early some slower-moving develop from particles that sun, particles he calls \u201cplanetesimals.\u201d particles stuck occasionally collided. together, forming AFTER 1980s Several apparently young larger particles. stars, such as Beta Pictoris, are found to be surrounded Over time, larger planetesimals formed. These aggregated into by disks of cool dust. a few large bodies, leading to the emergence of the planets. 1983 The Infrared Astronomical The planets formed from a disk of gas and dust. Satellite is launched. It observes that many stars have an excess of infrared radiation that could be explained if they were orbited by disks of cooler material.","NEW WINDOWS ON THE UNIVERSE 251 See also: Gravitational disturbances 92\u201393 \u25a0 The Kuiper belt 184 \u25a0 The Oort cloud 206 \u25a0 Inside giant molecular clouds 276\u201379 Viktor Safronov research. From the 1950s to the In Safronov\u2019s model, the 1990s, he worked on modeling planets formed out of dust and Viktor Sergeevich Safronov the idea that the planets formed ice particles, which stuck together was born in Velikiye Luki near within a disk of gas and dust. within a disk of material spinning Moscow in 1917, and graduated Today, Safronov\u2019s planetesimal around the newly formed sun. from Moscow State University hypothesis of planet formation Department of Mechanics and is widely accepted, although 1 A large cloud of gas and dust starts Mathematics in 1941. In 1948, alternative theories exist. After contracting and slowly rotating. he obtained a doctorate degree. the fall of the Soviet Union in Safronov spent a considerable 1991, he had the opportunity 2 The cloud flattens out into a part of his career working at to explain his ideas in the West. spinning disk with a denser, hotter the Schmidt Institute of the center, which forms the sun. Physics of the Earth, part of Key work the Academy of Sciences in 3 Solar radiation heats up Moscow. There, he met his wife, 1972 Evolution of the the inner solar system. Eugenia Ruskol, who for a time Protoplanetary Cloud and collaborated with him in his Formation of the Earth 4 Planetesimals rich in iron and silicate dust begin to form. Up to the 1940s, astronomers orbiting the early sun. Safronov\u2019s considered that the nebular breakthrough came when he 5 The solar system forms. hypothesis contained a major flaw calculated the effect on such a known as the \u201cangular momentum system of some particles colliding. models, which suggested that problem.\u201d They calculated that if He figured out the speeds at systems of particles orbiting the the solar system had formed out which they would collide. Particles early sun could indeed have formed of a contracting, rotating cloud the traveling at fast speeds would into a handful of planets. Recent sun should be spinning much faster simply bounce off each other. But observation of disks of cool dust than it actually is. During the first slower-moving particles would surrounding apparently young stars half of the 20th century, a number stick together, resulting in larger lend further support to the SNDM. \u25a0 of alternative hypotheses competed particles. As they grew bigger, with the nebular hypothesis. One the gravity of each particle would suggested that planets might have cause them to coalesce, forming formed from material pulled out of larger objects called planetesimals. the sun by a passing star; another that the sun passed through a The larger objects would dense interstellar cloud and emerged attract more mass, and the largest enveloped in the gas and dust from planetesimals would grow larger which planets coalesced. Eventually, and larger, until they had gathered solid reasons emerged for rejecting everything that lay within their these alternatives. gravitational reach. After a few million years, only a few planet- Safronov\u2019s theory develops sized bodies would remain. Undeterred, Safronov studied in detail how planets might have By the 1980s, there was wide formed in the disk of material agreement over the SNDM. One proposed by Laplace. This researcher suggested that the disk would have consisted of angular momentum problem could a collection of dust grains, ice be solved by dust grains in the particles, and gas molecules, all original disk slowing down rotation in the center. Others incorporated Safronov\u2019s ideas into computer","252 DCSWEOAITNLTEHAOCRNATNLOVYEREUBRTYERLSINAEORENSGE THE HOMESTAKE EXPERIMENT IN CONTEXT If the sun obtains energy from nuclear fusion, fast-moving low-mass particles called neutrinos should be produced. KEY ASTRONOMER Ray Davis (1914\u20132006) The detection rate in Neutrinos barely the interaction is likely interact with other BEFORE particles, but they may 1930 Austrian physicist to be very low. interact in a form of Wolfgang Pauli proposes radioactive decay. the existence of neutrinos. A very large detector is required. 1939 Hans Bethe outlines two main processes by which D uring the first half of the Although this theory was accepted stars obtain their energy. 20th century, scientists by the 1950s, it was not proven. In figured out a process by 1955, an American chemist named 1956 American physicists which the sun produces energy Ray Davis set out to show that the Clyde Cowan and Frederick by fusing hydrogen into helium. sun produces energetic neutrinos Reines confirm the existence In the sun\u2019s core, four hydrogen by detecting just a few of them. He of the antineutrino, the nuclei, which are single protons, faced a huge problem in achieving antiparticle of the neutrino. are changed into a helium nucleus, this goal, however. Apart from two positrons (also called anti- the fact that their existence was AFTER electrons), and two tiny ghostlike uncertain, scientists thought that 1989 The Kamiokande II particles called neutrinos, with neutrinos had zero electric charge experiment in Japan, the release of energy. The neutrinos and a tiny mass (if any at all), and organized by Masatoshi produced were envisaged to escape very rarely interacted with other Koshiba, demonstrates easily from the sun. particles. If the sun fuses hydrogen, conclusively that the sun is a source of neutrinos and confirms Davis\u2019s abnormally low detection rate.","NEW WINDOWS ON THE UNIVERSE 253 See also: Cosmic rays 140 \u25a0 Energy generation 182\u201383 \u25a0 Gravitational waves 328\u201331 Neutrino physics is largely and, from this, the rate at which Ray Davis an art of learning a great argon-37 should be produced deal by observing nothing. in the tank. Davis began counting Raymond Davis was born the actual numbers of argon-37 in Washington, D.C., in 1914. Haim Harari atoms produced. He earned a Ph.D. in physical chemistry from Yale University Israeli physicist Although Davis\u2019s experiment in 1943. Davis spent the later showed conclusively that the years of World War II in Utah, scientists thought, billions of sun does produce neutrinos, only observing the results of neutrinos should be passing through about one-third of the number chemical weapons tests. every square centimeter of Earth\u2019s of argon-37 atoms predicted From 1946, he worked at a surface every second, but perhaps by Bahcall were detected. The laboratory in Ohio, carrying only one in one hundred billion discrepancy between the number out research on radioactive might interact with atomic matter. of neutrino interactions predicted chemical elements. In 1948, and those detected became known he joined Brookhaven National Davis thought that neutrinos as \u201cthe solar neutrino problem.\u201d Laboratory, on Long Island, might be detectable through their which was dedicated to involvement in a type of radioactive Building on his 1989 work, finding peaceful uses for decay called beta decay. In theory, in 1999, Masatoshi Koshiba nuclear power. He spent the an energetic neutrino should be discovered the cause of the rest of his career studying able to convert a neutron in an discrepancy at Japan\u2019s huge Super- neutrinos. Davis retired from atomic nucleus into a proton. In Kamiokande neutrino detector. Brookhaven in 1984, but his experiments, Davis found Neutrinos were found to oscillate continued his involvement that, on very rare occasions, a between three different types\u2014 in the Homestake experiment neutrino passing through a tank the electron neutrino, the muon until it ended in the late 1990s. of a chlorine-containing substance neutrino, and the tau neutrino\u2014 would interact with the nucleus of while traveling through space. Davis met his wife, Anna, a stable chlorine atom to produce Davis\u2019s experiment had detected at Brookhaven Laboratory a nucleus of an unstable isotope only the electron neutrinos. \u25a0 and together they had five of argon called argon-87. children. He shared the Nobel Prize in Physics in Homestake experiment Davis\u2019s neutrino detector was 2002 with Masatoshi Koshiba In 1964, in what was called the placed deep underground to protect for pioneering contributions Homestake experiment, Davis it from cosmic rays (another possible to astrophysics. He died began a trial using a large tank source of neutrinos). in Blue Point, New York, of a chlorine-containing chemical age 91 in 2006. as a detector. An acquaintance of Davis, astrophysicist John Bahcall Key work calculated the theoretical number of neutrinos of different energies 1964 Solar Neutrinos II, that the sun should be producing Experimental","254 CAOSUTLADRNT\u2019THASTEEWE \u200a\u200aDISCOVERING BLACK HOLES IN CONTEXT B lack holes are invisible. was a strong source close to active They allow no matter star-forming regions of the Milky KEY ASTRONOMERS to escape, and, with the Way, in the constellation of Cygnus. Louise Webster (1941\u20131990) exception of low-level Hawking In 1973, Australian Louise Webster, Paul Murdin (1942\u2013)\u200a radiation at the event horizon, Briton Paul Murdin, and American Tom Bolton (1943\u2013) even swallow up electromagnetic Tom Bolton independently took light energy. Due to the difficulty measurements of the blue supergiant BEFORE of detecting an invisible object, star HDE 226868. They revealed that 1783 English clergyman John black holes remained purely it orbits an object far too massive Michell suggests the existence theoretical concepts up to the to be a neutron star. The only of a star whose gravity is so mid-20th century. However, such candidate for the invisible partner, strong that not even light can a concentrated mass ought still Cygnus X-1, was a black hole. Black escape it. to create observable effects. holes were now more than mere As it is dragged into a black hole, theoretical entities. \u25a0 1964 Cosmic X-rays are matter will be heated to millions detected by Geiger counters of degrees as it is ripped apart by An artist\u2019s impression shows matter in sounding rockets. gravitational forces, pouring out flowing from the blue supergiant star X-rays into space in the process. HDE 226868 into its black hole partner, 1970 Uhuru, the first X-ray Cygnus X-1. The star is losing one solar observatory satellite, is launched. In the 1960s, astronomers mass of material every 400,000 years. looked for cosmic X-ray sources AFTER with a series of balloon- and rocket- 1975 Stephen Hawking makes launched detectors. Many of the a bet with theoretical physicist hundreds of sources that they Kip Thorne that Cygnus X-1 is found were assumed to be \u201cX-ray not a black hole. binaries\u201d\u2014star systems in which a superdense stellar remnant, such 1990 Hawking concedes the bet as a neutron star, tears material and buys Thorne a subscription away from its visible companion. to Penthouse magazine. Among the first of these X-ray binaries to be discovered, in 1964, 2011 Further observations give Cygnus X-1 an expected mass See also: Supernovae 180\u201381 \u25a0 Cosmic radiation 214\u201317 \u25a0 Hawking radiation 255 of 14.8 suns (14.8 solar masses).","NEW WINDOWS ON THE UNIVERSE 255 BEMLAITCKRAHDOILAETSION \u200aHAWKING RADIATION IN CONTEXT T he mathematical theory of Quantum theory predicts that, black holes was pioneered throughout space, pairs of \u201cvirtual\u201d KEY ASTRONOMER in the 1910s by the German particles and their antiparticles Stephen Hawking (1942\u2013) physicist Karl Schwarzschild. should continually appear out of The object described by nothing, then annihilate (cancel BEFORE Schwarzschild was a non-rotating out back to nothing). One of each 1916 Karl Schwarzschild mass concentrated at a point of pair has positive energy, the other provides a solution to the field infinite density, called a singularity. negative energy. equations of general relativity, At a distance from this, known as allowing him to describe the the Schwarzschild radius, was an Some of these particle\u2013 gravitational field around a imaginary spherical surface called antiparticle pairs will appear just black holelike object. the event horizon. The gravity on outside the event horizon of a black the singularity side of this surface hole. It is possible that one member 1963 New Zealand was so great that nothing\u2014not even of the pair could escape\u2014observed mathematician Roy Kerr light\u2014could escape. In subsequent as an emission of (positive) radiation describes the properties decades, black hole theory evolved energy\u2014while the other falls into the of a rotating singularity. in various ways, but black holes black hole. In order to preserve the continued to be regarded as same total energy in the system, 1965 British mathematician entirely black, emitting no light. the particle that fell into the black Roger Penrose shows that the hole must have had negative energy. gravitational collapse of a giant Virtual particles This causes the black hole to slowly star could result in a singularity. In 1974, a big change occurred in lose mass-energy\u2014a process called black hole theory. British physicist black hole evaporation. 1967 American physicist John Stephen Hawking proposed that Wheeler coins the term \u201cblack black holes emit particles, known Hawking radiation remains a hole\u201d for the types of objects today as Hawking radiation. theoretical prediction. If it proves described by Schwarzschild, Hawking maintained that black correct, it means that black holes Kerr, Penrose, and others. holes are not completely black, do not last forever, which has since they emit radiation of some implications regarding the fate AFTER sort, if not necessarily light. of the universe, since it had been 2004 Stephen Hawking retracts thought that black holes would be an earlier claim that any object among the last objects in existence. \u25a0 entering a black hole is completely lost to the universe. See also: Curves in spacetime 154\u201355 \u25a0 The life cycles of stars 178 \u25a0 The heart of the Milky Way 297 \u25a0 Michell (Directory) 335","OTFHETETCRHI 1975\u2013PRESENT","IUNOMLPOHGY","258 INTRODUCTION NASA launches US astronomer Vera Rubin The Hubble Space the two Voyager publishes data showing Telescope enters orbit. spacecraft on a It provides the best-ever mission to tour the that the rotational speeds of images in the visible and galaxies indicate the presence near-visible spectrum. outer planets. of invisible \u201cdark matter.\u201d 1977 1980 1990 1979 1986 1995 US cosmologist Alan American Frank Shu The first brown dwarfs Guth develops the idea and colleagues present are detected, confirming that the early universe a theoretical prediction a new model for experienced a period star formation. made in 1962 by of rapid inflation. Shiv S. Kumar. M ost major discoveries mirrors are flexible, but kept (CCD). CCDs are electronic circuits in astronomy have precisely in shape by a network with light-sensitive pixels that been made possible by of computer-controlled supports generate electrical charges when advances in technology. Recent called actuators. light photons land on them. They developments have provided are far superior to photography for powerful tools to collect radiation ESO\u2019s choice of Chile was part sensing faint light and recording an from space and to process vast of the trend for astronomers to amounts of data, and the pace scour the world, testing for the We\u2019re going to need a of discovery has accelerated at a best sites where the air is clear, definitive quantum theory breathtaking rate. Microelectronics still, and dry, and the sky free of gravity, which is part of and computing capability, in from light pollution. Another a grand unified theory\u2014it\u2019s particular, have opened up new major center for astronomy was the main missing piece. possibilities over the last 40 years. established at the summit of the volcano Mauna Kea on the Big Kip Thorne Telescopes and detectors Island of Hawaii in 1967. This prime The New Technology Telescope site is now home to 13 telescopes. (NTT) opened by the European Southern Observatory (ESO) in Until the early 1970s, all the Chilean Andes in 1989 is astronomical imaging was carried an example of a telescope with out by means of conventional revolutionary innovations that have photography. Then, in the mid- subsequently become standard 1970s, a completely new way of equipment. Its main and secondary recording an image electronically became a practical reality. This was the charge-coupled device","THE TRIUMPH OF TECHNOLOGY 259 Swiss astronomers NASA\u2019s Curiosity rover After an 11-year journey, Didier Queloz and lands on Mars and begins NASA\u2019s New Horizons spacecraft makes its closest Michel Mayor to explore its surface. approach to Pluto, revealing discover the first details of its icy surface. exoplanet orbiting a sunlike star. 1995 2012 2015 1998 2013 2016 Cosmic expansion The European Southern The Ligo Scientific is found to be accelerating, Observatory opens Collaboration announces the suggesting the existence of a its Atacama Large mysterious \u201cdark energy.\u201d detection of gravitational Millimeter Array, a giant waves, confirming Einstein\u2019s radio telescope in Chile. general theory of relativity. object\u2019s brightness accurately, and Computers are indispensable be followed in real time, as the latest they made visible objects that had to theorists, too. Huge computing images from the Hubble Space previously been too faint to detect, power makes it possible to gain Telescope or the Curiosity rover on such as the small, icy worlds of the insight into what observations Mars are made instantly available. Kuiper belt beyond Neptune. are telling us about the way the universe works by creating Landmark discoveries Computing power simulations based on the laws of Of the many discoveries in recent Fast, reliable computers and physics. For example, computers decades that have had an impact an immense capacity for storing allow scientists to model ways in on our understanding, three stand data have been key not only to which the solar system may have out. The surprise finding in 1998 the way that telescopes and their formed and evolved. that the universe\u2019s expansion is instruments are constructed, accelerating showed that there but also to making sense of the Space exploration has now is a gap in fundamental theory. astronomical data they collect. pushed right out to the edge of By contrast, the detection of One major project alone, the Sloan the solar system, and no region gravitational waves in 2016 Digital Sky Survey, has collected of the planetary system remains confirmed Einstein\u2019s 100-year-old information about 500 million unexplored on some level. The theoretical prediction. Meanwhile, celestial objects since it began New Horizons mission passed the discovery of the first extrasolar in 2000. This database has been Pluto in 2015 and is moving through planet in 1995, and thousands more used to create a three-dimensional the Kuiper belt, while the Voyager since, has energized the search map showing how galaxies are spacecraft, launched back in 1977, for alien life. It is impossible even distributed across the universe, are now sending back data from to speculate where the next 20 revealing its largest structures. interstellar space. With the advent years may lead. \u25a0 of the internet, missions can also","GIANTA GRAND TOUR OF THE PLANETS EXPLORING THE SOLAR SYSTEM","","262 EXPLORING THE SOLAR SYSTEM IN CONTEXT more failures than successes, but A Titan 3E rocket lifts off carrying over the decade robotic spacecraft the Voyager 1 spacecraft as its payload. KEY ORGANIZATION began sending back close-up images The Titan 3E was the most powerful NASA\u2014Voyager mission of Venus and Mars. The NASA craft launch vehicle of its time. (1977\u2013) were part of the Mariner program, run largely from the Jet Propulsion outer planets and discovered that, BEFORE Laboratory (JPL) in California. The in 1978, all the outer planets would 1962 Mariner 2 passes Venus mathematicians at JPL perfected be on the same side of the sun. His in the first planetary flyby. the art of the \u201cflyby\u201d\u2014sending a calculations revealed that this had spacecraft on a trajectory that had not happened since 1801, and would 1965 Mariner 4 is the first it fly past a planet close enough to not occur again until 2153. craft to visit Mars. photograph and observe it, albeit too quickly to enter its orbit. In Flandro saw the opportunity 1970 Venera 7 makes the 1965, a graduate student named for a Grand Tour of the outer solar first soft landing on Venus. Gary Flandro, who was working at system, but the distances involved JPL for the summer, was given the were far beyond the capabilities of 1973 Pioneer 10 is the first task of figuring out routes to the the spacecraft of the day. In 1965, spacecraft to cross the asteroid Mars\u2019s alignment made it the belt en route to Jupiter. 1976 Viking 1 sends pictures from the surface of Mars. AFTER 1995 The Galileo spacecraft goes into orbit around Jupiter. 1997 Sojourner is the first rover to land on Mars. 2005 The Cassini orbiter releases the Huygens probe, which touches down on Titan. 2015 New Horizons makes the first flyby of Pluto and Charon. O n August 20, 1977, the Voyager 2 spacecraft was launched from Cape Canaveral in Florida. Two weeks later, its sister craft Voyager 1 was launched. Thus began the most ambitious exploration of the solar system ever. The launch was the culmination of more than a decade\u2019s work. The core mission would run for 12 years, but an interstellar mission continues. Going interplanetary By the early 1960s, both the Soviet and US space agencies were sending missions to other planets. There were","THE TRIUMPH OF TECHNOLOGY 263 See also: Life on other planets 228\u201335 \u25a0 The nebular hypothesis 250\u201351 \u25a0 Exoplanets 288\u201395 \u25a0 Understanding comets 306\u201311 \u25a0 Studying Pluto 314\u201317 closest planet to Earth at that time The best way to learn All the outer planets at 35 million miles (56 million km), about planets is to send will be close together but Neptune was 2.5 billion miles (4 billion km) away, and a journey robotic spacecraft for a short period. to it would take several years. to them. Planetary slingshots A Grand Tour could send probes to A Grand Tour spacecraft would study them throughout this period. have to change course several times in order to fly past all its planets. The Voyager program makes a Flandro\u2019s plan had to use gravity Grand Tour of the giant planets. assists to fling the craft from planet to planet. Also known as a from the planet\u2019s orbital motion. planet having added approximately gravitational slingshot or swing-by, The planet\u2019s gravity would speed twice the speed of the planet to a gravity assist had first been used up the craft as it made a loop its own velocity. A slingshot would by the Soviet Luna 3, which had around the planet. It would then not only redirect the craft, but also swung around the far side of the slow down again as it headed off accelerate it on to its next target. moon in 1959, photographing as into space, having done an about it went. It had never been used to turn. If the motion of the planet Taking a Grand Tour guide spacecraft as far from Earth were ignored, the craft\u2019s escape In 1968, NASA set up the Outer as the outer planets. The planned speed would be more or less equal Planets Working Group. It proposed slingshot required the craft to to its approach speed. However, the Planetary Grand Tour mission, approach the planet head-on, taking the motion of the planet into which would send one spacecraft traveling in the opposite direction account, the craft would leave the to visit Jupiter, Saturn, and Pluto, \u276f\u276f An artist\u2019s impression shows Voyager 1 in space. This craft and its twin, Voyager 2, communicate with Earth via radio waves transmitted and received by a 12-ft (3.7-m) dish. It was a chance that came around once in every 176 years and we prepared for it. Out of that emerged the greatest mission of planetary exploration to this day. Charles Kohlhase","264 EXPLORING THE SOLAR SYSTEM Jupiter\u2019s moon Europa was photographed by Voyager 2. It is covered in a thick crust of ice, which has been fractured and filled in with material from the moon\u2019s interior. and a second one toward Uranus moon known to have its own all the criteria and would take the and Neptune. The plan required atmosphere. This change meant spacecraft as close to as many a new long-range spacecraft and that the mission would be points of interest as possible. costs grew steadily. Then in 1971, budgeted as an exploration of the NASA canceled the Grand Tour as two gas giants, not a Grand Tour. Neither Kohlhase nor anyone it needed cash to fund the Space However, the spacecraft, code- else working on MSJ77 liked Shuttle program. named JST, was to have a back-up, the name. As the launch date JSX. Its mission would also include approached, a competition for a The exploration of the outer Jupiter and Saturn if JST failed. new name was organized. Nomad planets was handed back to the The X represented an unknown and Pilgrim made the shortlist, Mariner program. The mission was quantity. If required, JSX would but by the time the two identical named Mariner Jupiter\u2013Saturn, or go to Titan, but if JST achieved spacecraft were ready, they were MJS77 for short\u201477 referred to the its mission, then JSX would be known as Voyager 1 and Voyager 2. launch year. To reduce costs, Pluto sent to Uranus and Neptune. At 1,590 lb (720 kg), the two was removed from the tour Voyager spacecrafts were nearly itinerary. Instead, one craft was Mission profile 50 percent heavier than any to visit Jupiter, Saturn, and finally In 1974, mission design manager previous flyby craft. About 220 lb Saturn\u2019s huge moon Titan. Titan Charles Kohlhase began to make (100 kg) of that was scientific was considered more intriguing a master plan for the MJS77 equipment, comprising two than distant Pluto. It was larger mission. He had to consider every cameras, magnetic field sensors, than Mercury, and thought at the aspect, from the spacecrafts\u2019 spectrometers that would analyze time to be the largest moon in the design, size, and launch system light and other radiation to show solar system. It was also the only to the many variables they would which chemicals were present in encounter along their routes\u2014the atmospheres, and particle detectors Voyager 1 captured a 100-mile- radiation levels, light conditions, for investigating cosmic rays. (150-km-) high eruption on Jupiter\u2019s and contingencies for altering the In addition, the radio system moon Io. Strongly affected by Jupiter\u2019s missions. It took Kohlhase and his could be used for a variety of gravity, Io is the most volcanically team eight months to eventually experiments, such as probing active place in the solar system. settle on two trajectories that met atmospheres and Saturn\u2019s rings. The spacecrafts\u2019 trajectories were","THE TRIUMPH OF TECHNOLOGY 265 to be controlled by 16 hydrazine the compositions of the clouds and Titan in size, while images of thrusters. However, it would be measured the planet\u2019s immense Europa\u2019s eerily smooth yellowish too dark beyond the asteroid belt magnetic field. It also showed that disk had astronomers puzzled. for solar panels to generate enough Jupiter had a faint ring system. Its Voyager 2 arrived at Jupiter more electricity for the spacecraft, and most memorable discoveries came than a year later, and did not batteries would not last nearly long from the flybys of the Galilean approach as close as Voyager 1, but enough. The answer was nuclear moons. These were not sparse, it took some of the mission\u2019s most \u276f\u276f power in the form of radioisotope cratered balls but active worlds. thermoelectric generators (RTG), Photographs of Io showed the Voyager 2\u2019s images of Saturn\u2019s held out on a boom to isolate largest volcanic eruptions ever rings revealed a complex structure them from sensitive equipment. seen, spurting ash clouds into orbit. made of small satellites, none of Each RTG contained 24 balls of Fresh measurements of Ganymede which were larger than 3\u20136 miles plutonium that gave out heat, revealed that it superseded even (5\u20139 km) across. which was converted into an electric current by thermocouples. The power supply was built to last for nearly 50 years. Jupiter and its moons By December 1977, Voyager 1 had overtaken Voyager 2, which was taking a more circular trajectory. It reached the Jupiter system in January 1978. Most of Voyager 1\u2019s important discoveries were made in a frenetic 48-hour period around March 5, when it made its closest approach, coming within 217,000 miles (349,000 km) of the planet\u2019s cloud tops. In addition to sending back images, Voyager 1 analyzed The latter half of the next decade abounds in interesting multiple planet opportunities. Of particular interest is the 1978 \u201cgrand tour\u201d which would make possible close-up observation of all planets of the outer solar system. Gary Flandro","266 EXPLORING THE SOLAR SYSTEM Voyager 2 sent back this image of Neptune\u2019s ice moon Triton. During the craft\u2019s flyby, only the southern ice cap was visible. Highly reflective, it is made of frozen nitrogen and methane. The Titan trajectory then sent the craft over Saturn\u2019s pole and away to the edge of the solar system. Voyager 2 arrived at Saturn in August 1981, and was able to study the planet\u2019s rings and atmosphere in more detail, but its camera failed during much of the flyby. Fortunately, it was restored, and the order was given to continue to the ice giants. iconic images of Io transiting Saturn to prevent any damage Uranus and Neptune Jupiter. Voyager 2 also got a closer caused by Saturn\u2019s atmosphere Voyager 2 is the only craft look at Europa, showing that it and rings from endangering this to have visited the ice giants was covered in a crust of water crucial phase. The spacecraft Uranus and Neptune. It took 4.5 ice riven by cracks. Later analysis swung behind Titan so the sun\u2019s years to travel from Saturn to revealed that these cracks were light shone through the atmosphere, Uranus, where the craft passed caused by upwellings in a liquid allowing measurements of its 50,500 miles (81,500 km) above ocean under the crust, an ocean thickness and composition. the pale blue atmosphere. It that is estimated to hold at least looked at the planet\u2019s thin rings twice as much water as Earth and and discovered 11 new moons, which is thought by scientists all of which are now named after to be a prime candidate for the Shakespearian characters, as presence of alien life. is the rule for Uranus. The most curious thing to be examined Titan and Saturn By November 12, 1980, Voyager 1 Charles Kohlhase 2005. In the late 1970s, he was skimming 77,000 miles worked with computer artists (124,000 km) above the atmosphere Charles \u201cCharley\u201d Kohlhase to create accurate animations of Saturn. On the approach, and was born in Knoxville, of space missions for advancing despite some instrument failures, Tennessee, and graduated with the public understanding of it revealed details of the rings, a degree in physics. He briefly NASA\u2019s work. Now retired, which were made of billions of served in the US Navy before Kohlhase remains involved in chunks of water ice and were joining JPL in 1960, where he several projects that blend art as thin as 30 ft (10 m) in places. turned his life-long fascination and space science, aiming to Kohlhase had sent Voyager 1 to with exploration into work on educate and inspire the next visit Titan before approaching the Mariner and Viking projects, generation of rocket scientists before joining the Voyager team. and interplanetary explorers. In 1997, Kohlhase left Voyager to design the Cassini\u2013Huygens Key work mission to Saturn, which succeeded in dropping a lander 1989 The Voyager Neptune onto the surface of Titan in travel guide","THE TRIUMPH OF TECHNOLOGY 267 The golden records carried by the times a year, the craft spin around The spacecraft will be Voyager spacecraft included a selection to measure the cosmic rays around encountered and the record of music, greetings in 55 different them. This data shows that the languages, and images of humans, craft are approaching the edge of played only if there are animals, and plants. the heliosphere, the region of space advanced spacefaring that is influenced by the sun. Soon civilizations in interstellar on this otherwise relatively quiet they will enter interstellar space space. But the launching planet is the tilt of its axis, which and measure the cosmic wind from of this \u201cbottle\u201d into the is roughly 90\u00b0. As a result, Uranus ancient stellar explosions. cosmic \u201cocean\u201d says does not spin as it orbits, but something very hopeful \u201crolls\u201d around the sun. In 2025, the two spacecraft will about life on this planet. power down and go quiet forever, The final port of call was but their mission may still not yet Carl Sagan Neptune, reached in August 1989. be complete. A committee chaired This deep-blue planet was found by Carl Sagan selected content for will never be found by intelligent to have the strongest winds in a gold-plated phonograph record life, but the golden records are a the solar system, up to 1,500 mph (its analog groove would be easier symbol of the hope with which the (2,400 km\/h)\u2014nine times stronger to read than a digital format). They two interplanetary spacecraft were than anything experienced on included greetings from the world, sent on their way. \u25a0 Earth. The Voyagers\u2019 mission the sounds and sights of Earth, controllers were able to abandon and even human brain waves. Voyager 1 Heliosheath caution as the planetary mission The record is a calling card from drew to an end. Without regard humankind to an alien civilization. Solar wind for the safety of its final trajectory, The Voyagers are not heading for Earth Voyager 2 was redirected to fly any star systems; the closest they past Neptune\u2019s moon Triton. The will get is when Voyager 1 passes images of the huge ice moon showed 1.6 light-years from a star in 40,000 geysers blasting fountains of slush years\u2019 time. In all likelihood, they from the surface. By 2005, the Voyagers had reached the termination shock, where the solar wind slows and becomes turbulent as it mixes with the interstellar medium (matter in the space between star systems), entering the heliosheath region. By 2016, they were nearing the heliopause, where the solar wind is stopped by the interstellar medium. Continuing mission shock The Voyager program continues VoyagTere2rmination and the two craft are still in touch Heliopause with NASA. As of 2016, Voyager 1 was 12.5 billion miles (20 billion km) and Voyager 2 was 10 billion miles (16 billion km) away. Six","268 IN CONTEXT UMMNIOSISVSTEINROGSFETIHSE KEY ASTRONOMER Vera Rubin (1928\u2013) \u2005DARK MATTER BEFORE 1925 Bertil Lindblad calculates the likely shape of the Milky Way. 1932 Jan Oort finds that the rotational speeds of the Milky Way galaxy do not match the presumed mass. 1933 Fritz Zwicky suggests that a majority of the universe is made up of dark, invisible matter. AFTER 1999 It is discovered that dark energy is accelerating the expansion of the universe. 2016 The LIGO experiment detects gravitational waves, which offer a new method to map the distribution of dark matter across the universe. I saac Newton\u2019s universal law of gravitation is adequate for making calculations to launch a satellite into orbit, land a crew on the moon, and send a spacecraft on a grand tour of the planets. Newton\u2019s clear mathematics works well enough for most things on the solar system scale, but not on grander scales of the universe, where Einstein\u2019s relativistic theory of gravity is needed (pp.146\u201353). Nevertheless, Newton\u2019s law of gravitation was all that was required to reveal one of the biggest\u2014and as yet unsolved\u2014mysteries of astronomy: dark matter. In 1980, American astronomer Vera Rubin presented clear evidence that dark","THE TRIUMPH OF TECHNOLOGY 269 See also: Gravitational theory 66\u201373 \u25a0 Gravitational disturbances 92\u201393 \u25a0 The shape of the Milky Way 164\u201365 \u25a0 Supernovae 180\u201381 \u25a0 The Oort cloud 206 \u25a0 Dark energy 298\u2013303 We became astronomers her to stay in her home city of The outer regions of thinking we were studying the Washington, D.C., and raise her four galaxies move much more children. She chose to study the universe, and now we learn rotation of galaxies, specifically quickly than expected. that we are just studying the looking at the anomalous behavior To stop spinning 5 percent that is luminous. of the outer regions of galaxies. galaxies from disintegrating, Vera Rubin Spinning spirals they must contain a lot more The problem Rubin tackled was matter exists. Thanks to Rubin, the the fact that huge disks of stars mass than can be seen. general public learned that most of in nearby galaxies did not move This mass comes from the universe appears to be missing. in a way that was consistent with invisible dark matter\u2014 Newton\u2019s law of gravity: their there is six times more dark Throughout the 1960s and outer regions moved too quickly. matter in the universe than 1970s, the science of astronomy This curiosity was not new, but it was dominated by projects on a had previously been largely ignored. ordinary matter. grand scale, as researchers used massive instruments, often in Since the 1920s, when Bertil Most of remote parts of the world, to search Lindblad and others showed that the universe for exotic objects, such as black the Milky Way\u2014and by extension is missing. holes, pulsars, or quasars. By many other galaxies\u2014were disks contrast, Rubin was looking for of stars moving around a central a research area that would allow point, it was assumed that galaxies were orbital systems just like any other. In the solar system, near objects orbit at a faster speed than distant ones, so Mercury is moving much more rapidly than Neptune. This is because, following Newton, gravity decreases with a square of the distance. When the velocities \u276f\u276f Vera Rubin Born Vera Cooper in Philadelphia, concluded that galaxies would Rubin earned her first degree from clump together, a fact that was Vassar College in upstate New not fully explored until the work York, and then applied to go to of John Huchra in the late 1970s. Princeton. Her application was After teaching at a college in ignored because women were Maryland, Rubin returned to barred from joining the university\u2019s Georgetown, and then moved graduate astronomy program until to the Carnegie Institution of 1975. Instead Rubin pursued her Washington in 1965. It was here studies at Cornell University, that she conducted her work on where she studied under greats galactic rotation, and she has such as Richard Feynman and remained there ever since. Hans Bethe. She subsequently earned a Ph.D. from Georgetown Key work University in Washington, D.C., supervised by George Gamow. 1997 Bright Galaxies, Her thesis, published in 1954, Dark Matters","270 DARK MATTER of the planets are plotted against Oort\u2019s early measurements were No observational problem will their distance from the sun, the data inaccurate, while Zwicky\u2019s initial not be solved by more data. forms a smooth downward \u201crotation assessment was that \u201cdark matter\u201d curve.\u201d It followed that plotting the was 400 times more abundant than Vera Rubin orbital speeds of stars at different the matter of visible material\u2014a distances from the galactic center huge overestimate. This meant redshift and blueshift of objects, should produce a similar curve. that their findings were dismissed and calculate their relative speeds as measurement errors. In 1939, away from and toward Earth. In 1932, Dutch astronomer Jan American Horace Babcock again Oort was the first person to provide found anomalies in the rotation of After several years of slow but observational proof that the galaxy Andromeda and suggested that there careful work, Rubin had enough was a single orbital system made was some mechanism by which data to plot a rotation curve for up of a swirling spiral of stars, light from the missing matter was the galaxy. Instead of swooping in which the sun completed a being absorbed in the galactic core. downward like the curve of the 225-million-year orbit. However, in solar system, the speed data the course of his calculations, Oort Galactic rotation curve of the galactic curve stayed found that the motion of the galaxy More than 20 years later, Rubin relatively level with distance. suggested that it was twice as returned to the problem of galactic This meant that the outer regions massive as the total mass of visible rotation. Like Babcock, she chose of Andromeda were moving at the stars. He concluded that there must to focus on the rotation of the same speed as the areas nearer to be some hidden source of mass. Andromeda galaxy, the Milky Way\u2019s the center. If the galaxy\u2019s mass was A year later, the Swiss\u2212American nearest galactic neighbor. She limited to what could be observed Fritz Zwicky was studying the worked with her colleague Kent using telescopes, the outer regions relative motion of galaxies in the Ford at the Carnegie Institution of Andromeda would be moving Coma cluster. He found, again, of Washington to measure the faster than escape velocity, and that their motion suggested the velocities of objects in the outer they should simply fly off into mass of what could be seen was region of the galaxy. They did this space. However, they were clearly not the only stuff there. He named using a sensitive spectrograph, being held in place by the galaxy\u2019s the missing material dunkle which allowed them to detect the overall mass. Rubin calculated that Materie or \u201cdark matter.\u201d the total galactic mass required to hold the outer regions in orbit 150 Range was about seven times greater of error than the visible mass. The ratio Observation of matter to dark matter is today thought to be around 1:6. VELOCITY (KM PER SECOND) in each observation What is dark matter? Rubin\u2019s galactic rotation curve, 100 widely disseminated in 1980, was Observed rotation curve the visual proof that dark matter existed. As further evidence Rotation curve expected mounted, the mystery as to what from visible matter it might be remained. Dark matter 50 0 0 10 20 30 40 50 60 DISTANCE FROM CENTER (x 100 LIGHT YEARS) In the absence of dark matter, the velocities of objects in the outer regions of galaxies would be slower than the observed values. Here, the observed rotation curve is plotted against the expected curve from visible matter alone.","THE TRIUMPH OF TECHNOLOGY 271 Dark matter could be evidence that the universe is one of many that exist next to one another, in separate spatial dimensions, in a bubblelike multiverse. cannot directly be observed; only its effects are detectable, and the only effects that can be detected are from its gravity. It does not interact with the electromagnetic force, meaning that it does not absorb heat, light, or other radiation, nor does it emit any. Dark matter may be completely invisible. Possible sources is the WIMP\u2014Weakly Interacting However, the gravitational effects The simplest solution to the dark Massive Particle. This concept is of the matter in the hidden universes matter problem is the most literal. based largely on an idea in particle leaks through into this one through It comprises ultra-dense bodies of physics called supersymmetry. the warping of spacetime. ordinary matter that are too dark to It proposes a new explanation of observe. Astronomers have dubbed energy and ordinary matter. Energy Providing an explanation for dark these MACHOs, which stands for and matter form two distinct matter remains one of the biggest Massive Compact Halo Objects. groups of subatomic particles, prizes in astronomy. However, in MACHOs include objects like black and supersymmetry proposes that 1999, a possibly even more puzzling holes, neutron stars, and white and these groups interact thanks to the phenomenon was uncovered. It was brown dwarfs. They occupy the actions of \u201csuper particles,\u201d or discovered that 68 percent of the galactic halo, a dark and diffuse sparticles. Dark matter WIMPs universe was neither matter nor region that surrounds the main, might be sparticles that escaped dark matter, but so-called dark shining disk of a galaxy\u2014and this from their partners in the early energy. Dark matter makes up 27 is why it is difficult to see them. period of the universe, or they may percent; visible matter comprises MACHOs are clearly out there, but be objects that are there all along. a mere 5 percent. \u25a0 by current estimates they would only account for a tiny proportion Finally, dark matter might be For the moment we of dark matter. An alternative idea the observable effect of another might very well call them universe, or perhaps several, DUNNOS (for Dark Unknown that exist in a spatial dimension Nonreflective Nondetectable different from this universe. Their matter could be very close, a few Objects Somewhere). centimeters away, but because Bill Bryson the radiation from each universe is trapped inside its own spacetime, one universe can never see another. A huge ring of dark matter, which formed long ago in the collision between two massive galaxy clusters, is shown around the edge of this Hubble Space Telescope image in lighter blue.","272 \u200a\u200a\u200aNPGRERGOADAVTIUTICVYEE RPERPEUSLSSUIRVEES COSMIC INFLATION IN CONTEXT B y the 1970s, cosmologists (particles with only one magnetic were grappling with a variety pole). There are, however, none to be KEY ASTRONOMER of puzzles thrown up by the found, which suggests the universe Alan Guth (1947\u2013) Big Bang theory. In an attempt to cooled faster than expected. solve them, Alan Guth proposed a BEFORE stage of rapid inflation in the early A second problem arose from 1927 Georges Lema\u00eetre universe, caused by the effects the way space is amazingly \u201cflat,\u201d proposes that the universe predicted by quantum theory. meaning that it expands according arose from a single primordial to \u201cnormal\u201d Euclidean geometry (see atom. This is later named the The puzzles diagram opposite). A flat universe Big Bang theory. One of the problems with the would only have arisen if the density Big Bang theory came from the of the early universe matched a 1947 George Gamow and Grand Unified Theory (GUT), certain critical figure. Varying it Ralph Alpher describe how which describes how the forces slightly one way or the other would the elements hydrogen and of the universe (aside from gravity) have resulted in curved universes. helium were formed in the arose a fraction of a second after early universe. the Big Bang. The GUT predicted The final issue was the horizon that high temperatures at this time problem. Light from the edge of the 1964 The cosmic microwave would create bizarre features, such observable universe has taken the background is discovered to as so-called magnetic monopoles entire life of the universe to reach be a remnant of the Big Bang. Earth. As light\u2019s speed is constant, scientists know that it has not AFTER 1999 Dark energy is found to The Big Bang theory The first stage of the be accelerating the expansion predicts features universe after the Big of the universe. that are not seen in Bang may have been a the current universe. period of rapid expansion 2014 BICEP2 withdraws claims of finding evidence of inflation. called inflation. 2016 LIGO detects Inflation explains many of the features of the gravitational waves, offering universe, but there is no evidence that it is correct. a new way to observe the structure of spacetime.","THE TRIUMPH OF TECHNOLOGY 273 See also: The birth of the universe 168\u201371 \u25a0 The primeval atom 196\u201397 \u25a0 Searching for the Big Bang 222\u201327 \u25a0 Gravitational waves 328\u201331 Flat Curved Saddle-shaped It is not possible to visualize Alan Guth warped three-dimensional space, but if one dimension were removed, Born in New Jersey, Alan the geometry of space could be Guth received his doctorate shown as curved (where the internal in 1972 and specialized in angles of a triangle would add to more particle physics, pursuing than 180\u00b0); saddle-shaped (where the research into quarks angles would be less than 180\u00b0); and (elementary particles). By flat (Euclidean), where a triangle with the late 1970s, he had worked angles of 180\u00b0 would be drawn. at MIT, Princeton, Columbia, Cornell, and Stanford, as he had time to shine to the opposite cooled the universe rapidly, thus searched the country for a edge of the universe. So if no light, solving the GUT problem, and long-term academic position. energy, or matter has ever passed locked in the uniformity seen today. While at Columbia, Guth between the edges of the universe, Finally, the inflation ended as the became interested in the this leaves a puzzle as to why space density of the universe evened out Grand Unified Theory (GUT), appears so similar in every direction. at a value needed for a flat universe. which had been proposed in In 2014, BICEP2, an experiment 1974. He began developing The solution at the South Pole, reported ripples his inflation theory in 1978 Guth\u2019s theoretical solution to in space consistent with cosmic while at Cornell, after hearing these problems was to inflate the inflation. However, the claim was about the problem of the early universe using a quantum soon withdrawn. Cosmic inflation flatness of the universe, effect called a false vacuum, where remains unproven, but it is the best and shortly afterward, the positive matter energy was created current theory for the Big Bang. \u25a0 problems associated with as space expanded, equally GUT. While at Stanford, balanced by an increase in gravity The recent developments in he then came across the (a form of negative energy). In the cosmology strongly suggest horizon problem, and went first 10\u201335 seconds after the Big on to publish his famous Bang, space doubled in size 100 that the universe may be theory in 1981. He is now times over, going from a billionth the ultimate free lunch. a professor at MIT, where of the size of a subatomic particle he helps with the search for to the size of a marble. This means Alan Guth evidence of cosmic inflation. that, at the very beginning, the edges were close enough to mix Key works and become uniform, thus solving the horizon problem. During 1997 The Inflationary inflation, space expanded faster Universe: The Quest for a than the speed of light. (The New Theory of Cosmic Origins speed of light is only a speed 2002 Inflation and the New Era limit through space.) The inflation of High-Precision Cosmology","274 \u200a\u200a\u200aBBG\u200a EUALBOABNXLTIEEHLSIEKASEPUPSRETFARARUCCTETOSUORFES REDSHIFT SURVEYS IN CONTEXT S ince the 1920s, the study space. Geller and Huchra\u2019s work of the redshift of distant provided valuable clues to the KEY ASTRONOMERS galaxies has revealed the nature of the very early universe. Margaret Geller (1947\u2013) scale of space and the way in John Huchra (1948\u20132010) which the universe is expanding A redshift survey uses a wide- in all directions. Redshift occurs angle telescope to select target BEFORE when a light source is moving away galaxies, generally millions of 1842 Christian Doppler from the observer (p.159). In the light-years away. Astronomers describes how wavelengths can 1980s, redshift surveys made by compare the light from each galaxy change due to relative motion. American astronomers Margaret with benchmark wavelengths to Geller and John Huchra, working determine the redshift, and thus 1912 Vesto Slipher discovers at the Harvard\u2013Smithsonian Center the distance the light has traveled, that galaxies are redshifted for Astrophysics (CfA), gave an allowing them to plot the positions by the Doppler effect. even clearer picture of the universe, of many galaxies. Huchra started showing that galaxies cluster the first redshift survey in 1977; 1929 Edwin Hubble uses around great voids of empty by its completion in 1982, he had redshift to show that distant mapped 2,200 galaxies. galaxies are moving away faster than nearer ones. Margaret Geller Margaret Geller earned a Ph.D. from Princeton in 1975, and 1980 Alan Guth proposes that a took various fellowships before rapid expansion, called cosmic joining the Harvard\u2013Smithsonian inflation, shaped the universe. Center for Astrophysics in 1983. She worked there with John AFTER Huchra, analyzing the results of 1998 The Sloan Digital Sky his redshift survey. Geller went Survey finds walls, galaxy on to lead the second (CfA2) sheets, and filaments many redshift survey. She is a frequent hundreds of light-years long. public speaker and has made several films about the universe, 1999 A redshift survey of including Where the Galaxies supernovae reveals that the Are, which takes viewers on universe\u2019s expansion is a graphical voyage around speeding up. the large-scale objects of the observed universe.","THE TRIUMPH OF TECHNOLOGY 275 See also: Spiral galaxies 156\u201361 \u25a0 Beyond the Milky Way 172\u201377 \u25a0 Cosmic inflation 272\u201373 \u25a0 A digital view of the skies 296 Galaxies form clusters and superclusters that fill wide, and 16 million thick. It was narrow bands of space around vast empty voids. the first of several supersized structures now known. These voids are too large ever to have contained matter. The size of the voids puzzled They must have been present in the very early universe. astronomers. They were too large to have been emptied completely Before Huchra began his survey, walls enclosing vast voids, like the by the gravitational collapse of it was known that galaxies surface film of a bubble. She found material that formed the stars and existed in clusters. For example, the first \u201cgreat wall\u201d of galactic galaxies, which meant that they the Milky Way is one of at least superclusters in 1989. The exact must have been empty since 54 galaxies in a cluster called the size of CfA2 Great Wall is still the beginning of the universe. Local Group, which is about 10 unclear, but it is estimated at 700 Cosmologists theorize that the million light-years wide. It was million light-years long, 250 million large-scale order of superclusters assumed that clusters were evenly and voids is the legacy of quantum spread. However, by 1980, Huchra fluctuations during the inflationary had shown through his redshift epoch of the universe. Quantum survey that dozens of clusters fluctuations are fleeting changes form superclusters hundreds of in the amount of energy at points millions of light-years wide. in space. These small but highly The Local Group is part of the significant irregularities were Laniakea Supercluster, which locked into the fabric of the contains 100,000 other galaxies. universe in the first fraction of a second of its existence, and Walls of galaxies remain today. They are now the In 1985, Geller began the CfA2 vast areas of void permeated by Redshift Survey, taking 10 years a tangled pattern of matter. \u25a0 to map 15,000 galaxies. Her survey confirmed that superclusters were themselves arranged in sheets and This computer simulation of a portion of the universe shows the distribution of 10,000 galaxies, which cluster in long filaments and \u201cwalls,\u201d in between vast empty voids.","276 IN CONTEXT IFSNRTSOAIRMDSETFOHOUERTM KEY ASTRONOMER Frank Shu (1943\u2013) \u2005INSIDE GIANT MOLECULAR CLOUDS BEFORE 1947 Bart Bok observes dark nebulae and suggests that they are sites of star formation. 1966 Frank Shu and Chia-Chiao Lin develop the density wave theory to explain spiral arms in the Milky Way. AFTER 2003 The Spitzer Space Telescope, an infrared observatory, is launched. It produces the best view yet of stellar nurseries. 2018 First light on the James Webb Space Telescope will allow astronomers to study protostars inside dark Bok globules. S tars form inside dark globules of dust and gas that are called giant molecular clouds (GMCs). However, the process by which a cloud of gas transforms into an embryonic star, or protostar, has never been observed, partly because the process must take millions of years, and partly because even the most advanced telescopes find it difficult to penetrate the dark density of the cloud. Without observational evidence, astrophysicists must construct mathematical models for what they think is happening inside those dark globules. The most consistent model of star formation was derived by US mathematician Frank Shu.","THE TRIUMPH OF TECHNOLOGY 277 See also: Stellar composition 162\u201363 \u25a0 Nuclear fusion within stars 166\u201367 \u25a0 Energy generation 182\u201383 \u25a0 Dense molecular clouds 200\u201301 \u25a0 Studying distant stars 304\u201305 \u25a0 Jeans (Directory) 337 \u25a0 Ambartsumian (Directory) 338 The Pillars of Creation are vast clouds of gas and dust where new stars are made. This famous image was captured by the Hubble Space Telescope in 1995. Shu and his colleagues Fred Adams and Susana Lizano at the University of California at Berkeley presented their model in 1986 after 20 years of work. The inside-out model GMCs are vast regions of the In the mid-1960s, Shu and the Shu\u2019s system is called the \u201csingular galaxy filled with hydrogen atoms renowned Chinese\u2212American isothermal model,\u201d or the \u201cinside- and molecules mixed with specks mathematician Chia-Chiao Lin out model.\u201d It is built from the of dust and ice. Typically, a GMC modeled the rotation of a spiral complex mathematics that define contains 100,000 solar masses of galaxy, and showed that the arms the dynamics of gas clouds, taking material, which is a mixture of are located at density waves\u2014 into account factors such as primordial gases produced by the \u201ctraffic jams\u201d of stars. Such density temperature, density, electrical Big Bang and the remnants of long- waves sweep up interstellar charge, and magnetism. Shu\u2019s dead stars. GMCs are mostly found material into GMCs, and this model works by making the process in the spiral arms of a galaxy. triggers the formation of stars. \u276f\u276f self-similar. A starting condition that causes some of the gas cloud to contract into a dense core will result in the same\u2014or similar\u2014 conditions, which cause more gas to join the core, and so on. This process was found to be stable enough to keep the young star together as it grew. Earlier models had failed because they could not find a way to balance the mechanisms that were pulling the gases in and pushing heat out; as a result, these models ended with the young star disintegrating. Stars are dense balls of They must have formed Material from near superhot hydrogen. from clouds of hydrogen the middle contracted gas in interstellar space. first, and then drew in the outer regions. Stars form from the inside out.","278 INSIDE GIANT MOLECULAR CLOUDS Frank Shu\u2019s inside-out model The impact of a density wave, or and the contracting gravitational describes the four-stage formation something more violent such as force in the core wins out over of a star from a giant molecular cloud. a blast from a nearby supernova, the outward pressure. 1 Cores form within GMCs as magnetic creates turbulence inside a GMC. forces and turbulence calm. However, highly tangled magnetic The inner region of the cloud fields run through the cloud, and core contracts to form a dense ball 2 A protostar with a surrounding nebular these stop the turbulence from of gas at the center. This is the disk forms at the center of a cloud core, ripping the cloud apart. The protostar. Protostars do not form collapsing from inside out. magnetism also acts to prevent in a rapid process, but take millions the cloud from collapsing in on of years, and millions more to itself under its own gravity. grow into a full-fledged star. The protostar is also surrounded by Cloud cores a disk of material formed by the Over millions of years, the magnetic system\u2019s rotation, and wave upon pressure and turbulence in the wave of material is pulled in from gases dissipate, creating regions the surrounding envelope of gas. of calm, where slowly rotating With each wave, the mass of the \u201ccloud cores\u201d form. On closer protostar and its more diffuse disk inspection, GMCs are not uniform, grows, and its gravity grows with but made up of dark fragments it. The increasing gravity steadily or clumps of denser material, pulls in material from farther known as Bok globules. Each away, hence the description of the globule is thought to contain process as an \u201cinside-out collapse.\u201d several cloud cores. The star gathers mass Shu\u2019s model supposes that the The protostar warms up as it core becomes a single isothermal becomes denser, but it is still too (equal-temperature) sphere, or small and cold to produce energy something very close to it. This by fusing hydrogen in its core. means that the gravity pulling the The force of all of the new material ball of gas together is balanced by landing on its surface also adds the outward pressure of the moving to the heat signature given out by gas and its magnetic forces. Such the protostar. At this stage, it is a state can never persist for long, giving out only faint infrared and 3 A stellar wind breaks out along the Frank Shu model while at Berkeley and rotational axis of the system, creating was the head of the astronomy a bipolar flow. Born in Kunming, China, department there by the time 4 The infall of material ends, revealing a Frank Shu moved to the United he presented the full review of newly formed star with a circumstellar disk. States when he was six to his isothermal sphere model in join his father, an academic 1986. Today, Shu holds tenure mathematician, who was at Berkeley. In recent years he beginning research at MIT. has used his knowledge of Frank followed his father to astrophysics to tackle climate MIT, where he completed change. He often works in a degree in physics in 1963. collaboration with his graduate While there, Shu worked students, who are collectively on the density wave theory known as the \u201cShu Factory.\u201d of spiral arms. He later moved to Harvard to complete his Key work doctorate in astronomy in 1968. Shu worked on his protostar 1981 The Physical Universe","THE TRIUMPH OF TECHNOLOGY 279 microwave radiation, which makes full-fledged stars destined to An infant star sits at the center of it hard to see. Eventually, however, live short, bright lives. However, two nearly symmetrical jets of dense the protostar gathers enough mass smaller stars\u2014those less than 8 gas. Known as CARMA-7, the star is for fusion to begin, but initially only solar masses\u2014have not begun a about 1,400 light-years from Earth. the deuterium, a heavy isotope of full fusion process and so are known hydrogen, begins to burn. Unlike as pre-main-sequence (PMS) stars. form from PMS stars that are an \u201cadult\u201d star, a protostar releases less than 2 solar masses. They are its heat entirely by a process of A PMS star still has a disk of considerably wider and less dense convection. Heat from its core rises material spinning around it. Some than their adult forms, and appear up to the surface in the same way of that will be dispersed by the much brighter as they give out that hot water in a pan rolls around stellar wind into the wider GMC. light from larger surface areas, as it boils. The convection and What remains, around the smaller frequently punctuated by high- rotation of the star create a strong stars especially, is likely to form energy outbursts of X-rays. magnetic field, which pushes out into gas giant planets, and perhaps This energy is the product of from each pole, clearing a narrow later, rocky ones as well. gravitational contraction, not hole in the envelope of gas and Final ignition nuclear fusion. It takes about dust. The growing protostar\u2019s heat The final phase of star formation is 100 million years for the PMS star and a stellar wind of plasma are a contraction of the fast-spinning to compress itself enough to begin directed away from the star via PMS star. Red, orange, and yellow burning hydrogen, and by that these polar jets. These features, dwarfs (M, K, G, and F type stars) time, it will have lost half to three- explained by Shu\u2019s model, have quarters of its initial mass. Larger been confirmed by observations. A protoplanetary disk surrounds PMS stars (those between 2 and 8 the young star HL Tauri in the solar masses) take a different route Becoming a star, almost constellation Taurus. The dark patches to achieving fusion and form rare A star with the mass of the sun are thought to represent the possible blue dwarfs (A and B type stars). spends about 10 million years as positions of newly forming planets. a protostar. As its mass increases, PMS stars are the earliest the angle of its polar jets widens, stage of star formation that have pushing away more of the gas been seen clearly. Infrared space cloud. Eventually, the protostar\u2019s telescopes such as Spitzer and stellar wind blasts out from the Hubble have given faint glimpses entire star\u2019s surface, and it clears of protostars but mostly they are its gas cloud away completely. At too heavily shrouded by the dark this point, the young stellar object dust clouds. NASA\u2019s new infrared is revealed for the first time. Giant James Webb Space Telescope is stars (above 8 solar masses) have designed to be sensitive enough already started burning hydrogen to see through that dust, so perhaps by this point and have become soon the moment when a star is born may at last be observed. \u25a0","IWNRITNIKMLEES OBSERVING THE CMB","","282 OBSERVING THE CMB IN CONTEXT T he Cosmic Microwave The Cosmic Microwave Background, or CMB, Background Explorer (COBE) KEY ASTRONOMERS was discovered in 1964. spent four years in space collecting George Smoot (1945\u2013) This is the afterglow of the Big information about the CMB, scanning John Mather (1946\u2013) Bang and it is as near as scientists the celestial sphere every six months. can get to observing the event BEFORE that brought the universe into to the inflationary model of the 1964 The cosmic microwave existence, 13.8 billion years ago. early universe proposed by background\u2014an echo of the Linking the structures observed American Alan Guth. Big Bang itself\u2014is discovered. in the universe to the features 1981 Alan Guth proposes discerned in the CMB remains The CMB is a flash of radiation cosmic inflation, a theory in a key challenge for cosmologists. that was released about 380,000 which fluctuations of energy years after the Big Bang, at density were locked into space Wrinkled time the time the first atoms formed during the Big Bang. The first great breakthrough (pp.196\u201397). The expanding 1983 Redshift surveys show came from the Cosmic Microwave universe had cooled enough for that galaxies are clustered Background Explorer, known as stable ions (positively charged around voids of nothingness. COBE, a NASA satellite launched nuclei) of hydrogen and helium in 1989. The detectors on COBE, to form, and then, after a little AFTER designed and run by George more cooling, the ions began to 2001 Wilkinson Microwave Smoot, John Mather, and Mike collect electrons to make neutral Anisotropy Probe is launched Hauser, were able to find the atoms. The removal of free electrons to refine the map of the CMB. oldest structures in the visible from space led to the release of 2015 The Planck observatory universe, described by Smoot as photons (particles of radiation). studies the CMB to refine the \u201cwrinkles in time.\u201d These wrinkles age of the universe to 13.813 in otherwise uniform space were Those photons are visible now billion years +\/- 38 million years. once dense regions containing the as the CMB. The CMB comes from Combining this with other data, matter that would form stars and the whole sky, without exception. the latest estimate is 13.799 galaxies. They correspond to the It has redshifted (the wavelengths billion years +\/- 21 million years. large-scale galaxy superclusters have stretched), and it now has and great walls seen in the wavelengths of a few millimeters, I always think of universe today, and add weight while the original radiation\u2019s space-time as being the wavelengths would be measured real substance of space, in nanometers (billionths of a meter). and the galaxies and the stars just like the foam on the ocean. George Smoot","THE TRIUMPH OF TECHNOLOGY 283 See also: The birth of the universe 168\u201371 \u25a0 Searching for the Big Bang 222\u201327 \u25a0 Cosmic inflation 272\u201373 \u25a0 Redshift surveys 274\u201375 \u25a0 Tegmark (Directory) 339 One of the key observations of The cosmic microwave background the CMB came in the 1970s, and is a flash of radiation produced removed any doubt that it was an 380,000 years after the Big Bang. echo of the Big Bang. This was the discovery that the thermal The CMB\u2019s wavelength The CMB is not spectrum of radiation from the shows how hot the smooth and uniform, but CMB tallied very closely with that contains tiny fluctuations of a theoretical black body (p.225). universe was when the CMB was emitted. in temperature. Black bodies Black bodies do not really exist\u2014 These fluctuations, or they cannot be made and no object \u201cwrinkles in time\u201d, are the oldest structures observed in the universe functions as black bodies do in theory. ever found and represent the formation However, the CMB is the closest of the first stars and galaxies. match that has ever been found. heated. Heating it more makes it other astronomical objects are a A black body absorbs all orange, and eventually the bar will much closer match to a black body, radiation that hits it. Nothing is glow \u201cblue hot.\u201d Metalworkers learn and so the color, or wavelengths of reflected. However, the absorbed to roughly judge the temperature of their emissions, can be compared radiation adds to the thermal iron by its color. The metal is not to the thermal spectrum of a energy of the object, and this particularly close to a black body in theoretical black body to give is released as radiation. In 1900, the theoretical sense, but stars and a relatively precise temperature. \u276f\u276f German Max Planck, the founding figure of quantum physics, showed that the spectrum of radiation released by a black body is entirely dependent on temperature. In an everyday example of radiation varying with temperature, an iron bar glows red when first George Smoot After a childhood in Florida and Time with Keay Davidson Ohio, Smoot began his career as to explain the discovery. a particle physicist working at Smoot won the Nobel Prize in MIT. His interests switched to 2006, along with John Mather, cosmology and he moved across for his work on COBE. He the country to the Lawrence reportedly gave his prize Berkeley National Laboratory. money to charity. However, It was there that Smoot studied three years later, Smoot won the CMB and developed ways an even greater sum when he of measuring its radiation. bagged the $1 million jackpot on the TV game show Are You Smoot\u2019s early work involved Smarter Than a 5th Grader? fitting detectors to high-altitude U2 spyplanes, but in the late Key work 1970s, he became involved in the COBE project to take his detector 1994 Wrinkles in Time (with into space. After his success with Keay Davidson) COBE, Smoot cowrote Wrinkles in","284 OBSERVING THE CMB The temperature of the CMB today is in places. These denser areas, or [COBE has made] the a chilly 2.7 K. The thermal spectrum anisotropies, were where the stars greatest discovery of the at that temperature contains no and galaxies formed. COBE was century, if not of all time. visible light, which is why space looks sent into space to take a close look black to human eyes. However, the at the CMB to see if it could find Stephen Hawking spectrum has redshifted (stretched) any anisotropies, to find out whether over time as the universe has the CMB changed, however slightly, 2 K (colder than space itself) using expanded. Extrapolating back to depending on where it looked. 100 gallons (650 liters) of liquid the moment the CMB was emitted helium. George Smoot ran the gives an original temperature COBE\u2019s mission Differential Microwave Radiometer of about 3,000 K. The color of A mission to study the CMB from (DMR), which mapped the precise radiation at this temperature is space had been in the planning wavelengths of the CMB, while orange, so the CMB started out stages since the mid-1970s. John Mather was in charge of as a flash of orange light that shone Construction of COBE began in 1981. FIRAS, the Far-InfraRed Absolute out from every point in space. It was initially designed to enter Spectrophotometer, which collected polar orbit (its orbit passing over both data on the spectra of the CMB. Smooth signal poles). However, the Challenger These two experiments were The early observations of the CMB disaster of 1986 grounded the shuttle looking for anisotropies. The third suggested that it was isotropic, fleet, and the COBE team had to look detector on COBE had a slightly which means that its spectrum is for another launch system. In 1989, different goal. The Diffuse Infrared the same everywhere. In cosmology, the satellite was launched using Background Experiment, run the terms density, energy, and a Delta rocket, and it was placed by Mike Hauser, found galaxies temperature are somewhat in a sun-synchronous geocentric that were so ancient and far synonymous when discussing orbit\u2014orbiting in a way that saw away that they are only visible by the early universe. So the isotropic it pass over each place on Earth at their heat radiation (or infrared). nature of the CMB suggested that, the same time of day. This worked in those early days, space had a just as well as a polar orbit in that COBE\u2019s instruments created uniform density, or spread of energy. it allowed COBE to point away from the most accurate map of the However, this did not tally with the Earth and scan the entire celestial CMB to date. However, it was not developing theories of the Big Bang, sphere, strip by strip. a simple surveying job. Smoot and which demanded that matter and Mather were interested in primary energy were not evenly spread The spacecraft carried three anisotropies\u2014that is, the density through the young universe, but instruments, all protected from differences that were present at had been concentrated together the sun\u2019s heat and light by a cone- the time the CMB formed. To find shaped shield, and chilled to these, they needed to filter out the secondary fluctuations caused by obstacles that lay between COBE The full-sky map produced by WMAP in 2011 showed many fine details of the isotropy of the CMB. Colder spots are blue, while hotter spots are yellow and red.","THE TRIUMPH OF TECHNOLOGY 285 In addition to mapping the CMB, WMAP measured the age of the universe as 13.77 billion years, dark matter as 24.0 percent of the universe, and dark energy as 71.4 percent. and the edge of the universe. Dust clouds and the effects of gravity had interfered with the radiation on its long journey to Earth. The data from the three instruments were used to detect and correct these so-called secondary anisotropies. Tiny fluctuations Since COBE, two subsequent However, no known galaxy can After 10 months in space, COBE\u2019s missions have added detail to be seen forming in the CMB. The helium ran out, which limited the picture of the CMB. Between CMB radiation detected today has the function of the two infrared 2001 and 2010, NASA\u2019s Wilkinson traveled from near the edge of the detectors, but the DMR continued Microwave Anisotropy Probe observable universe over the course working until 1993. By 1992, the (WMAP) mapped the CMB to of most of the age of the universe. COBE team\u2019s analysis had shown a higher resolution than COBE. Astronomers can only see 13.8 billion what they were looking for. The Then, from 2009\u20132013, the ESA\u2019s light-years away, but most of the CMB, and thus the early universe, Planck Observatory produced the universe now lies farther away was not a uniform blob of energy. most accurate map to date. than that. The galaxies forming in Instead it was riddled with tiny the CMB are now far beyond what but significant fluctuations. The Every wrinkle on the map is the can be observed, and are receding differences were minute, with seed from which an entire galaxy faster than the speed of light. \u25a0 density variations of about 0.001 formed about 13 billion years ago. percent. However, the pattern was enough to explain why the contents of the universe are clustered together, while the rest of space is made from vast empty voids. Improving resolution of the CMB COBE\u2019s imaging of the CMB shows WMAP\u2019s map of the CMB shows Planck\u2019s resolution is 2.5 times greater slight variations in a 10-sq-degree greater detail within the same panel, than that of WMAP, showing features as panel of its all-sky map, proving that revealing smaller-scale features that small as 1\u2044 12 of a degree. This is the most the CMB is not uniform. COBE could not identify. detailed map of the CMB to date.","286 BTHELETKIUSIPREERAL EXPLORING BEYOND NEPTUNE IN CONTEXT The outer solar system contains the leftover material from the formation of the planets. KEY ASTRONOMERS David Jewitt (1958\u2013) Some of the material travels Short-period comets Jane Luu (1963\u2013) from the edge of the solar must come from a nearer source. BEFORE system in the form of 1930 American astronomer long-period comets. Clyde Tombaugh discovers Pluto orbiting beyond Neptune. It is The Kuiper belt, a theoretical reservoir of icy bodies beyond the initially identified as the ninth orbit of Neptune, could be the source of short-period comets. planet but is later reclassified. I n 1950, Dutch astronomer Jan belt beyond Neptune. But the 1943 Kenneth Edgeworth Oort proposed that a spherical Dutch\u2212American astronomer suggests that Pluto is just shell of potential comets Gerard Kuiper argued in 1951 that, one of many objects in the surrounds the solar system half a although there was once such a outer solar system. light-year away. The so-called Oort belt, it would have been scattered cloud was the source of long-period away by the gravity of the outer 1950 Fred Whipple describes comets, which took millennia to planets. It was a puzzle, and comet the icy nature of comets as orbit the sun. But the source of nuclei that far away would be too \u201cdirty snowballs.\u201d the short-period comets that orbit faint for even the best telescopes. the sun every few centuries must AFTER be nearer. In 1943, Irish scientist In the 1980s, sensitive new CCD 2003 Sedna is discovered Kenneth Edgeworth speculated (charge-coupled device) detectors orbiting 76 AU\u22121,000 AU from that the comet reservoir was a became available. With these, the sun, beyond the outer edge astronomers at last had a chance of the Kuiper belt. 2005 Eris is seen in the disk beyond the Kuiper belt. 2008 Two Kuiper Belt Objects are classified as dwarf planets along with Eris, Pluto, and Ceres.","THE TRIUMPH OF TECHNOLOGY 287 See also: The Kuiper belt 184 \u25a0 The Oort cloud 206 \u25a0 Studying Pluto 314\u201317 The egg-shaped dwarf planet Haumea hangs in the sky above one of its two moons, Namaka. Haumea, discovered in 2004, is the third-largest dwarf planet. of spotting small icy objects beyond Neptune. Americans David Jewitt and Jane Luu were among the astronomers who set about the difficult task. After five years of searching, in 1992, Jewitt and Luu discovered an object formally designated 1992 QB1, the first body to be found beyond Neptune since Pluto, and the first evidence that the Kuiper belt was real. Cubewanos and plutinos 45 AU from the sun. These KBOs this region is the source of short- More than 1,000 Kuiper Belt Objects are sometimes called \u201ccubewanos.\u201d period comets. In 2006, Eris was (KBOs) are now known and there Closer in, at around 40 AU, the designated a dwarf planet along are probably thousands more. gravity of Neptune has thinned with Pluto. Since then, two more They are designated as asteroids, out the Kuiper belt, leaving a family cubewanos, Makemake and but unlike most asteroids, KBOs of objects (including Pluto itself) Haumea (Haumea is orbited by two are typically a mixture of rock called \u201cplutinos,\u201d in orbits that are small moons), have been classed and ices. The largest are several unaffected by Neptune\u2019s gravity. as dwarf planets, with many more hundred miles across and many Beyond the main Kuiper belt lies KBOs listed as candidate dwarf of them have moons. a region called the \u201cscattered disk,\u201d planets. Scientists believe that which includes the large objects Eris these KBOs resemble the primitive 1992 QB1 is typical of the KBOs and Sedna. It is now believed that bodies that formed the planets. \u25a0 in the most densely populated middle part of the Kuiper belt, about Gerard Kuiper Gerard Kuiper was born surrounded the young sun in the Netherlands in 1905. changed scientists\u2019 view At a time when few other of the early solar system. astronomers were interested in the planets, Kuiper, working In the 1960s, Kuiper mostly at the University of helped identify landing sites Chicago, made many discoveries on the moon for the Apollo that changed the course of program and cataloged space science: he found that the several binary stars. He died Martian atmosphere was mostly of a heart attack in 1973, at age carbon dioxide, that Saturn\u2019s 68. Since 1984, the Kuiper Prize rings comprised billions of chunks has been awarded annually by of ice, and that the moon was the American Astronomical covered in a fine rock dust. In Society to recognize achievement 1949, Kuiper\u2019s idea that the in planetary science, a field planets were formed from of astronomy in which many a cloud of gas and dust that consider Gerard Kuiper to have been the pioneer.","MOST STARS PARLE AORNBITEETD BSY EXOPLANETS","","290 EXOPLANETS I n 1995, two Swiss astronomers, For more than 2,000 years, Michel Mayor and Didier people have dreamed of IN CONTEXT Queloz, researching at the Observatoire de Haute-Provence finding other habitable worlds. KEY ASTRONOMERS near Marseille, found a planet Michel Mayor Michel Mayor (1942\u2013) orbiting 51 Pegasi, a sunlike Didier Queloz (1966\u2013) star 60 light-years away in the The discovery of 51 Pegasi b constellation of Pegasus. This marked the final milestone in a BEFORE was the first confirmed observation process that has forced astronomers 1952 US scientist Otto Struve of a true extrasolar planet, or to abandon any lingering notion proposes the radial velocity exoplanet\u2014a planet beyond the that Earth occupies a privileged method to find exoplanets. solar system. It was orbiting place in the universe. a main sequence star, and was 1992 The first such planet is therefore assumed to have formed Copernican principle found, orbiting a pulsar and by the same process as that In the 1950s, the Anglo\u2212Austrian not a main sequence star. which created the solar system. astronomer Hermann Bondi had described a new way for humans AFTER Mayor and Queloz named the to think about themselves, which 2004 Construction begins new planet 51 Pegasi b, but it is he called the Copernican principle. on the James Webb Space unofficially known as Bellerophon According to Bondi, humankind Telescope, which will be after the hero who rode Pegasus, could no longer regard itself as able to image exoplanets. the winged horse of ancient Greek a unique phenomenon of central myth. Its discovery prompted a importance to the universe. On 2005 The Nice model offers a major hunt to find more exoplanets. the contrary, humans should now new idea for the evolution of the Since 1995, several thousand solar system that places the exoplanets have been found, giant planets closer to the sun. many in multiple star systems. Astronomers now estimate that 2014 The construction of the there is an average of one planet European Extremely Large around every star in the galaxy, Telescope begins. although this is probably a very conservative figure. Some stars 2015 Kepler 442-b, an Earth- have no planets, but most, like sized rocky exoplanet around the sun, have several. an orange dwarf, is discovered. Michel Mayor was born in sensitive enough to spot giant Michel Mayor Lausanne, Switzerland, and has planets as well, and, following spent most of his career working their 1995 discovery, Mayor is at the University of Geneva. His currently the chief investigator interest in exoplanets arose from at the HARPS program his earlier study of the proper for the European Southern motion of stars in the Milky Way. Observatory in Chile. His team To measure this motion more has found about half of all the accurately, he developed a exoplanets discovered to date. series of spectrographs, which In 2004, Mayor was awarded eventually culminated in ELODIE. the Albert Einstein medal. The ELODIE project with Didier Queloz was initially intended to Key work search for brown dwarfs\u2014objects that were bigger than planets 1995 A Jupiter-mass Companion but not quite large enough to be to a Solar-type Star (with stars. However, the system was Didier Queloz)","THE TRIUMPH OF TECHNOLOGY 291 See also: The Copernican model 32\u201339 \u25a0 Radio telescopes 210\u201311 \u25a0 Studying distant stars 304\u201305 \u25a0 Looking farther into space 326\u201327 \u25a0 Kumar (Directory) 339 understand that their existence Unseen Star wobbles from one is insignificant in the context planet position to another of the universe. Longer wavelength The principle is named after indicates the star Nicolaus Copernicus, who changed is retreating. the way humankind saw itself by relegating Earth from the center of Shorter wavelength indicates the solar system to one of several the star is advancing. planets that orbited the sun. By the late 20th century, successive When a large Jupiter-like planet orbits its discoveries had moved the solar star, it exerts a gravitational pull on the star. system from the center of the Both star and planet revolve around a common universe to a quiet wing at center of gravity. The \u201cwobble\u201d in the star\u2019s the edge of a galaxy containing orbit allows the planet to be detected. 200 billion other stars. The galaxy was not special either, simply one In 1952, US astronomer Otto Struve That detector was a spectrograph of at least 100 billion arranged in had suggested that this kind of named ELODIE developed by vast filaments that extended for star wobble could be detected Mayor in 1993. ELODIE was about hundreds of millions of light-years. as small fluctuations in a star\u2019s 30 times more sensitive than any Nevertheless, planet Earth and the spectrum. As the star moved away previous instrument. Even then, solar system were still regarded as from Earth, its emissions would it was only capable of measuring very special\u2014since there was no be slightly redshifted from the velocity changes of 7 miles\/s evidence that any other stars had norm. When it wobbled back again (11 km\/s), which meant it was planets, let alone planets capable toward the observer, the light limited to detecting planets of supporting life. Since Mayor\u2019s would be blueshifted. The theory about the size of Jupiter. and Queloz\u2019s discovery, however, was solid but detecting the wobble this idea has also succumbed to required an ultrasensitive detector. Improving the search the Copernican principle. In 1998, an even more sensitive We are getting much spectrograph, named CORALIE, Wobbling light closer to seeing solar was installed at La Silla Observatory Queloz and Mayor found 51 Pegasi b systems like our own. in Chile, which again was using a system called Doppler searching for planets using the spectroscopy. Also known as Didier Queloz radial velocity technique. In 2002, the radial velocity or \u201cwobble\u201d Michel Mayor began overseeing method, Doppler spectroscopy HARPS (High Accuracy Radial can detect an exoplanet by its velocity Planet Searcher) at the gravitational effects on its host star. same site, using a spectrograph The star\u2019s gravity is far greater than capable of detecting exoplanets that of the planet, and this is what about the size of Earth. The wobble keeps the planet in orbit. However, method of detection was very slow, the planet\u2019s gravity also has a small so new techniques of spotting effect on the star, making it wobble exoplanets were developed. \u276f\u276f back and forth as the planet moves around it. The effect is tiny: Jupiter changes the sun\u2019s speed by about 12 miles\/s (7.4 km\/s) over a period of 11 years, while Earth\u2019s effect is only 0.1 miles\/s (0.16 km\/s) each year.","292 EXOPLANETS The most successful method Ssun shade Photometer High gain was the transit method, which antenna looked for periodic changes in the brightness of a star. These changes Radiator were very small and happened when a planet transited the star, Avionics passing between the star and the observer, and causing it to dim very Solar array slightly. The best place to look for exoplanets by the transit method The Kepler observatory Star was out in space and so, in 2009, looked outward from the plane trackers the Kepler observatory, named of the ecliptic, so that Earth, after the man who first described the moon, and the sun Solid state planetary orbits (pp.50\u201355), was did not obscure the view. recorder launched to do just that. unable to see individual exoplanets, that. Those that were correctly Staring at one place but could identify stars that were oriented would only transit their star Kepler was placed in a heliocentric likely to have them. once every orbital period (the planet\u2019s orbit, trailing behind Earth as it year), so Kepler\u2019s method was better circled the sun. The craft was Kepler could only detect the at finding planets that orbited close designed to keep its aperture firmly transits of exoplanets with orbital to their star, taking a few years and fixed on a single patch of space, paths that crossed the spacecraft\u2019s months (or even weeks and days) called the Kepler field. This made line of sight. Many exoplanets would to complete each revolution. up only about 0.25 percent of the be orbiting at the wrong angle for whole sky, but the spacecraft could see 150,000 stars in that area. To find exoplanets, Kelper would have to concentrate on this single field of view for years on end. It was According to the Copernican principle, if the sun has Candidate stars a planetary system, it is likely that other stars do as well. By the start of 2013, Kepler had identified about 4,300 candidate Many exoplanets have Exoplanets can be stars that might have extrasolar been found by several detected by their effects planetary systems. Unfortunately, different techniques. the guidance system used to keep on their host star. Kepler locked on target then failed, bringing its planet hunt to an end Statistical analysis of Most stars are about three years sooner than the data reveals how orbited by planets. expected. However, the data it common exoplanets are. had collected was enough to keep researchers busy for years to come. Kepler\u2019s candidate stars could only be confirmed as planetary systems using radial velocity measurements from ground-based observatories, such as HARPS in Chile and the Keck Telescope in Hawaii. (Radial velocity is the velocity of the star in the direction of Earth.) So far, about a tenth of Kepler\u2019s candidate stars","THE TRIUMPH OF TECHNOLOGY 293 have proved to be false positives We were not expecting example, 51 Pegasi b was the first but, after three years of analysis, to find a planet with a of many \u201chot Jupiters.\u201d These have the program had identified 1,284 4-day [orbital] period. No a mass similar to Jupiter\u2019s and a exoplanets, with more than 3,000 one was expecting this. large size that shows that they are stars left to examine. The statistics mostly made of gas. 51 Pegasi b is for the exoplanets in the Kepler field Michel Mayor half as massive as Jupiter, but is are striking\u2014most stars are part slightly larger. This gas giant orbits of a planetary system. This means distance, and the temperature its sunlike star every four days. that the number of planets in the of the star. This tells them what That means it is much closer to universe is likely to exceed the the planet is probably made of its star than Mercury is to the sun. number of stars. and allows them to conjecture Such proximity means it is tidally what the surface conditions are locked to the star\u2014one side always The amount of dimming during likely to be. faces the scorching stellar surface, a transit gives an indication of how and the other always faces away. big an exoplanet might be, but the Hot and super Jupiters Many hot Jupiters have been found. study of an exoplanet\u2019s size and The exoplanets discovered so far They have confounded scientists, characteristics is still in its early have added a host of weird worlds who are trying to understand how stages. The light reflected from to the neat family portrait that is gas planets can exist so close to a planet is about 10 billion times the sun\u2019s planetary system. For a star without evaporating. Some fainter than the star it orbits. exoplanets are dozens of times Astronomers are waiting for the more massive than Jupiter, and James Webb Space Telescope in are known as \u201csuper-Jupiters.\u201d \u276f\u276f 2018 and the European Extremely Large Telescope in 2024 to image The \u201csuper-Jupiter\u201d Kappa this light directly and analyze the Andromedae b, shown here in an chemistry of exoplanets. Until then, artist\u2019s render, has a mass of 13 times they have to speculate using very Jupiter\u2019s. It glows a reddish color, and little data: an approximate mass may yet be reclassed as a brown dwarf. of the planet, its radius, the orbital","294 EXOPLANETS 2011-BLG-262, is thought to have that it orbits once an Earth day a satellite, and could be the first and has a surface temperature Red dwarfs with rocky exoplanet found with an exomoon. that would melt iron. Life seems planets could be ubiquitous highly unlikely there, but the Another class of planet are hunt continues for rocky planets in the universe. called the super-Earths. These have that might be more hospitable. Phil Muirhead a mass 10 times that of Earth but less than that of an ice giant like Astrobiologists\u2014scientists who Professor of Astronomy Neptune. Super-Earths are not search for alien life\u2014focus on the Boston University rocky but made from gas and ice: particular conditions that all life alternative names for them are needs. When choosing likely places These super-Jupiter planets do mini-Neptunes or gas dwarfs. to look, they assume that alien life- not appear to grow in size as their forms will require liquid water and mass increases. For instance, Living planets carbon-based chemicals, just like Corot-3b is a super-Jupiter that Earth\u2019s solar system has terrestrial life on Earth. Living planets would is 22 times as heavy as Jupiter planets (planets with a rocky also need an atmosphere to shield but more or less the same size, due surface), of which Earth is the the surface from damaging cosmic to its gravity holding its gaseous largest. So far, exoplanet searches rays and to act as a blanket that contents together. Astronomers have struggled to find many retains some of the planet\u2019s heat have calculated that the density terrestrial planets, because they during the night. of Corot-3b is greater than that are generally small and beyond of gold and even osmium, the the sensitivity of the planet The region around a star where densest element on Earth. detectors. The first confirmed the temperatures would allow terrestrial exoplanet was Kepler- planets to have liquid water, carbon Brown dwarfs and rogues 10b, which is three times the mass chemistry, and an atmosphere, When a super-Jupiter reaches of Earth and is so close to its star is known as its habitable zone, 60 Jupiter masses, it is no longer also called the \u201cGoldilocks zone\u201d\u2014 regarded as a planet, but as a brown dwarf. A brown dwarf is essentially a failed star\u2014a ball of gas that is too small to burn brightly through nuclear fusion. The brown dwarf and its star are seen as a binary star system, not a planetary one. Some super-Jupiters and small brown dwarfs have broken free of their star to become free-floating rogue planets. One, named MOA- Kepler 10b in the Draco constellation is shown transiting its star in an artist\u2019s impression. Its extremely hot surface temperature and dizzying orbit mean life there is improbable.","THE TRIUMPH OF TECHNOLOGY 295 A hotter star The sun A cooler star The size of the habitable zone (green) depends on the size of the star. The red zone is too hot, while the blue zone is too cold. The habitable zone is closer to cooler stars than it is to hotter stars. The size of a planet, the shape of its orbit, and the speed of its rotation between night and day also affect its habitability. like Baby Bear\u2019s porridge in the the atmospheric chemistry for signs may throw light on that process. fairy tale, \u201cnot too hot, not too cold.\u201d of life, such as the presence of Even if life is found, it is likely The size and locations of habitable elevated levels of oxygen, produced that most extraterrestrial natural zones depend on the activity of by photosynthesizing life-forms. histories will not have moved the host star. For example, if Earth How life evolved from nonliving beyond microorganisms. As were orbiting a K-type star, an material on Earth is still a mystery every step toward evolving more orange dwarf that is considerably but the study of Earth-like planets complex life-forms becomes ever cooler than the sun (the sun is a more unlikely, so alien civilizations G-type, or yellow dwarf), it would If we keep working as well and that match humankind\u2019s will be need to orbit at about one-third its we keep being as enthusiastic a lot less common. However, if current distance to receive the \u2026 the issue about life on other only G-type stars, like the sun, are same amount of warmth. counted, there are about 50 billion planets will be solved. in the galaxy. It is estimated that Of the thousands of exoplanets Didier Queloz 22 percent of them have an Earth- that have been identified, only like planet in their habitable zones, a tiny proportion are candidates which equals 11 billion possible orbiting in their star\u2019s habitable Earths. Adding in other types zones, with Earth-like conditions of stars such as orange and red for life\u2014rocky surface with liquid dwarfs, that number rises to 40 water. Typically, they are larger billion. Even if the probability of than Earth, and very few have good civilizations evolving is one in prospects for being Earth-like. If a billion, the chances are that and when Earth-like planets are humankind is not alone. \u25a0 found, astrobiologists will look at","296 \u200a\u200aUMTHNAEIPVMEORFOSSTETHEEAVMEBRITIOUS A DIGITAL VIEW OF THE SKIES IN CONTEXT S et up to produce \u201ca field A cube section of the SDSS sky map guide to the heavens,\u201d the shows the intricate distribution of KEY ASTRONOMER Sloan Digital Sky Survey matter in space. The tangles of light Donald York (1944\u2013) (SDSS) began operating in 1998. are interconnected galaxies. The ambitious goal was to make BEFORE a map of the universe on an onto a spectroscope. From 1929 Edwin Hubble proves immense scale\u2014not just a survey these accurate galactic spectra, that the universe is expanding. of objects on a celestial sphere, the astronomers can figure out but a three-dimensional model of how far away each galaxy is. Data 1963 Maarten Schmidt a large portion of deep space. The collection began in 2000 and is discovers quasi-stellar objects, project was initially headed by US expected to continue until 2020. or quasars, which turn out to astronomer Donald York, but is The information gathered so far be young galaxies. now a collaboration between 300 has revealed galaxies in clusters astronomers from 25 institutions. and superclusters, and even galactic 1999 Saul Perlmutter, Brian SDSS uses an 8-ft 3-in (2.5-m) \u201cwalls\u201d\u2014immense structures Schmidt, and Adam Riess telescope at Apache Point, New containing millions of galaxies, show that the expansion of Mexico. The telescope\u2019s wide-angle forming a tangled cosmic web the universe is increasing camera has digitized objects visible with vast voids in between. \u25a0 due to the mysterious effects from the northern hemisphere. of \u201cdark energy.\u201d From the 500 million objects AFTER visible, the brightest 800,000 2004 Construction begins galaxies and 100,000 quasars on the James Webb Space were selected, and their sizes Telescope, which will use and positions in the sky accurately infrared to see the first stars transposed as holes drilled into that formed after the Big Bang. hundreds of aluminum disks. When fitted to the telescope, a disk blocks 2014 Approval is given for unwanted light, and feeds the light the European Extremely Large from each target galaxy into its Telescope, which will have a own dedicated optical fiber and 128-ft (39-m) segmented main mirror, making it the most See also: Beyond the Milky Way 172\u201377 \u25a0 Quasars and black holes 218\u201321 \u25a0 sensitive optical telescope ever. Studying distant stars 304\u201305 \u25a0 Looking farther into space 326\u201327","THE TRIUMPH OF TECHNOLOGY 297 HOCUAENRRTBGROAARLLSABXALYMACASKSHIOVELE \u200aT\u200a HE HEART OF THE MILKY WAY IN CONTEXT I n 1935, Karl Jansky found a In 1980, Hawaii\u2019s Keck Observatory source of radio waves named began measuring the speed of stars KEY ASTRONOMER Sagittarius A (Sgr A) at the orbiting close to the galactic center. Andrea Ghez (1965\u2013) center of the Milky Way. Hidden This data made it possible to from light telescopes by cosmic calculate the mass of the invisible BEFORE dust, the radio waves emanated object inside Sgr A*. Ghez\u2019s team 1971 British astronomers from several sources. In 1974, radio found that the stars closest to Sgr A* Martin Rees and Donald telescopes pinpointed the most were orbiting at a quarter of the Lynden-Bell propose that intense source, named Sagittarius speed of light. Such speed indicated the radio waves emanating A* (Sgr A*). It was small and an immense gravitational presence: from Sagittarius A are produced intense X-rays, suggesting a black hole 4 million times heavier produced by a black hole. that matter at the heart of the than the sun, which must have galaxy was being ripped apart swallowed up stars and other black AFTER by a gigantic black hole, emitting holes when the galaxy was young. \u25a0 2004 A smaller black hole X-rays in the process. However, this is discovered in orbit around remained hypothetical until Andrea An X-ray flare shoots from the black Sagittarius A*. Ghez, an astronomer at UCLA, hole at the heart of the Milky Way. The used a method for observing stars discovery suggests all galaxies may 2013 The Chandra X-ray through the dust using infrared. have black holes at their hearts. Observatory sees a record- breaking X-ray flare from Sagittarius A*, perhaps caused by an asteroid entering the black hole. 2016 The LIGO experiment makes the first detection of gravitational waves, capturing the moment when two black holes merged into one. See also: Radio astronomy 179 \u25a0 Discovering black holes 254 \u25a0 Studying distant stars 304\u201305","COSMIC EXPANSION IS ACCELERATING DARK ENERGY"]