P Jupiter’s Great RedSpot,amassivestablestormphotographed byVoyager 2in1979. space science, ofthe Voyager probes’ mission to the giant planets. Roger D.Launius heliopause the Beyond 30 | NATURE30 | 2015 VOL | MARCH 519|5 Neptune late the —between 1970s and the SystemSolar —Jupiter, Saturn, Uranus and encountered larger the outer planets of the and launched probes twin 1970s, the in the add to its cachet. Conceived 1960s inthe assured, although account. efforts to popular this planetary-science an in-depth, nuanced understanding of big Marsseveral probes, brings writing deft and of many missions, space-science including System Solar the and aveteran beyond. Bell, ager 1 and missions to edge the of presents of eventful story the NASA’s Voy vating read. In it, scientist planetary Jim Bell BOOKS &ARTS SPACE SCIENCE Voyager’s status legendary long has been science, and sermon on part delights the of memoir,art anecdotal part history The Interstellar AgeThe The Interstellar Age The COMMENT savours amasterful account, by aveteran ofinterplanetary is acapti will - - © 2015 Macmillan Publishers Limited. Allrights reserved but NASA it deemed expensive too to build a stage. The four-planet was scenario possible, spacecraft’s velocity and reduce times. flight movement and gravity —could increase the a slingshot harnessing effect, planet’s the fly-bythe of each planet, a — giants, ‘grand inaplanetary tour’. During would enable close-up of observation the planets gather on one sideof Sun. the This and System’s Solar the Earth four giant scientists that realized 176years, once every Flandroaerospace engineer Gary and other craft that could’. The probes are, inessence, ‘the little space stellar mission at edge the of Solar the System. remit,original now they continue an inter late 1980s.Having gone far beyond their Bell describes the politics the of planning the describes Bell writes aboutBell how, early inthe 1960s, - - moon Titan, during it which acom revealed grammed for encounter aclose with Saturn’s some.then was, for example, pro how craft objectives the achieved their —and tute of Technology inPasadena, describes as an undergraduate at Insti California the faster, shorter on 5 trajectory September. 20 August 1977,and Voyager 1followed on a would allow. NASA launched Voyager 2 on into probes the as US$875-million the budget but as engineers much designed longevity was downgraded to aJupiter–Saturn fly-by, forspacecraft an extended mission. Voyager Dutton: 2015. JIM BELL Mission Forty-Year Voyager Age: Insidethe The Interstellar of planets, the rings and satellites, and took sentThey back more than 100,000images a total of 48 moons around gas the giants. canic features. The Voyagers explored also on Io, amoon of Jupiter with numerous vol ing previously unknown activity geological systems of rings and find magnetic fields, and scientists made it work. was hugely but taxing, mission engineers opportunities. Successfully capturing data each, to advantage take ory of scientific had only about 5,000words’ worth of mem grammed on-board the computers, which probes flew, controllers constantly repro most giant reports planets. how, Bell as the missionplanetary ended. tinue on to Uranus and Neptune, craft’s the System’sSolar elliptical plane; unable to con VoyagerBut fly-by this deflected 1out of the missionCassini at dawn the of century. this sustainedthe investigations of Huygens– the for investigation, scientific paving way the for and water ice. It showed that Titan was ripe plex world with an atmosphere, thickclouds Bell, who hung who Bell, out team with science the The probes explored giant the planets’ Voyager 2continued on to two the outer in telling human the Earth. sibilities of life beyond suchideas pos as the ing intriguing new was formed and rais questions about how it helping to resolve key SystemSolar science, mation revolutionized readings. The infor and radiationspectra ments, chemical magnetic measure Bell is at hisBell best ------­ - - - - -

NASA/SPL BOOKS & ARTS COMMENT

The identical Voyager probes launched MATHEMATICS in 1977 and are still travelling.

stories of discovery, excitement and public engagement. He describes the extension Groping in the dark for of the Voyager mission to the heliopause,

NASA/JPL/SPL where the Sun’s energy is overpowered by interstellar forces. Ed Stone, who has glimpses of beauty been chief scientist for Voyager since its inception, evinced the excitement of a Amir Alexander relishes two accomplished accounts self-confessed non-party animal. “I can of the life mathematical. still remember taking the data home every night, and putting the plots on the refrig- erator,” he tells Bell. “I couldn’t stop think- ne evening in 2009, French math- Birth of a Theorem: A Mathematical ing about them, wondering what would ematician Cédric Villani stepped Adventure happen next.” into his children’s room. He locked CÉDRIC VILLANI Bodley Head/Faber and Faber: 2015. Voyager 1 is now more than 130 astro- Othe door, turned off the light and began to nomical units (au) from the Sun (1 au pace, pondering the statistical properties of Mathematics Without Apologies: Portrait of is the distance between the Sun and plasma. A few metres away, his wife, Claire, a Problematic Vocation Earth, around 150 million kilometres), was in the kitchen, cooking dinner for the MICHAEL HARRIS Princeton Univ. Press: 2015. and Voyager 2 is at more than 107 au. family. The contrast, Villani concedes in They continue to take readings of the his engaging Birth of a Theorem, was “a heliopause. bit much”, yet immediately after dinner he Thanks to astronomer Carl Sagan, returned to the dark room to grapple for one of Bell’s heroes, both probes contain hours with his elusive proof. messages from Earth: gold-plated cop- Anyone reading that anecdote will feel per phonograph records encoded with sympathy for Claire as she tries to preserve

JOEL SAGET/AFP/GETTY 115 images of scenes from Earth, audio family normality. Anyone who has seri- greetings in 55 languages, and 90 minutes ously engaged with mathematics will also of music from Bach to Chuck Berry, along understand her husband. Perhaps more with playing instructions. This message than any other field, mathematics pulls the in a bottle is one of the mission’s best- practitioner away from the ‘normal’ world known attributes, and Bell explains well of things and people into a strange alternate its publicity value and how it represents a universe, in which we catch glimpses of feel-good sentiment about the possibility beauty and coherence, but spend most of our of encountering interstellar life. time groping in the dark. In Birth of a Theo- The Voyagers demonstrate the remark- rem, Villani offers one way of straddling that able advances in robotic space explora- divide; in Mathematics Without Apologies, tion over the past almost 40 years, and fellow mathematician Michael Harris pre- suggest that subsequent missions may sents a very different one. Together, they yield even more exciting results. Such provide an unmatched perspective on life Cédric Villani studies the maths of plasmas. follow-ups as the mission to Jupi- in this “problematic vocation” by two of its ter, Huygens–Cassini to Saturn and New leading practitioners. portrayals of mathematicians and physicists Horizons to the Kuiper belt including Birth of a Theorem is the story of Villani’s past and present. The grumpy, grey-haired Pluto may herald even more ambitious quest to give a full mathematical account Étienne Ghys of Lyons and Chinese expat missions — to Titan, for instance, where of Landau damping. Whereas gas becomes Alice Chang of Princeton alternate with the they might sail on a hydrocarbon sea, or increasingly disordered over time as entropy autocratic Lev Landau in 1960s Moscow and to Jupiter’s moon Europa, to explore an increases, plasma spontaneously stabilizes, the ever-present shadow of Albert Einstein at ice-covered liquid-water ocean that has with no increase in entropy. Soviet physicist the Institute for Advanced Study in Prince- the potential to harbour life. Lev Landau was the first to mathematically ton. Much of Villani’s e-mail correspondence I believe that NASA’s greatest achieve- describe this improbable phenomenon, but with Mohout is reproduced, chronicling ment is the Apollo Moon programme. The he used a simplified model that left many moments of triumph and despair. odyssey of the Voyagers certainly vies for unconvinced. Working closely for several Charismatic and flamboyantly dressed, second place. Bell appropriately quotes years with mathematician Clément Mohout, Villani is the opposite of the ‘mathematical historian Stephen Pyne: “The Voyagers Villani succeeded, and he was awarded a hermit’ and annoyed by the stereo­type. He were special when they launched. They Fields Medal in 2010. attends a recital by one of his children, joins have become more so thanks to their lon- Villani’s quest takes him across the world, his family at the American Museum of Natu- gevity, the breadth of their discoveries, from Lyons, France, to Princeton, back ral History in New York and travels a long way the cultural payload they carried, and the to Paris and on to Hyderabad in India. At to attend a concert by rock band Têtes Raides. sheer audacity of their quest.” ■ every stop, he talks to local mathematicians, Yet he studies the mathematics of galaxy for- demonstrating that, mation during the recital, works out a step in Roger D. Launius is associate director for all its abstractness, NATURE.COM his proof on the bus from the museum, and for collections and curatorial affairs at the mathematics can be an For more on science explains his research to a stranger who drives Smithsonian Institution’s National Air intensely social activ- in culture, see: him back from the concert. The mathematical and Space Museum in Washington DC. ity. The book is sprin- nature.com/ life, in his telling, is a delicate dance between e-mail: [email protected] kled with brief, telling booksandarts the demands of the ‘real’ world and the

5 MARCH 2015 | VOL 519 | NATURE | 31 © 2015 Macmillan Publishers Limited. All rights reserved