1984 duce huge amounts of martian methane, duce hugeamountsofmartian gas. the produce Atreya thinksitmightpro- floor,water liquid chemically altersbasaltto which on Earth’s hasbeenobserved ocean tinization couldbetheculprit.Inthisprocess, knownprocess low-temperature as serpen- Instead,source. a little-knowngeochemical invoke to soon too microbesasthe martian regions. concentrated inspecific thenthegas but wouldn’t surface, martian be yearshave could delivered methanetothe impact inthepastfewthousand observed. not A freakcometary sulfur dioxide,which is would alsoproduce work. Volcanicactivity of themethanedon’t tions fortheexistence alternative explana- many Arbor,Ann versity ofMichigan, Sushil Atreya oftheUni- Indeed,says scientist planetary byproduced livingorganisms. methane in Earth’sis atmosphere gas. After all, almost allthe ing intheiceandproducing sible evidence thatbacteriaareliv- pos- as researchers hailedthefind 1 October2004,p.29).Many ice ( subsurface be where surface therealsoappearsto martian craft detectedmethaneabove areasofthe Space pean Agency’s MarsExpressspace- Last year, aspectrometeronboardtheEuro- Then Gone With theWind? Gone With Then RockyBirth, Methane: Martian Meeting Division for Division Meeting Planetary Sciences interesting dynamically.” “2003 EL SaysRabinowitz: strange satellitearesomehow related. systemcould have formed or whether the rapid rotationthe and It’show unclear the distance ofalmost50,000kilometers. small satelliteorbitingtheminiplanet atasurprisingly large Rabinowitz andhiscolleagueshave also detected a Hawaii, Using the 10-meter Keck Telescope Kea, Mauna at body. hours 3.9 fastest the is ever measured for large a solar system its period of shape results from theobject’s rapid rotation; measuring 1960 as 2003EL known object, The Yaleof University. Rabinowitz David says the outersolarsystemisalmosttwiceaslongitwide, rapidly A rotating rugbyball. From Snapshots the Meeting But, But, Atreya announcedatthemeeting,it’s 61 a o ut ea i sPuo but it’smore much may notquitebeasbigPluto, 61 hastheshapeofasquashedrugby ball, , × Science 1520 × 00klmtr.Theelongated 1000 kilometers. , A recentlydiscovered miniplanetin 3SPEBR20 O 0 CEC www.sciencemag.org SCIENCE VOL309 23 SEPTEMBER 2005 Atreya says—more thanenoughtoexplain duce upto200,000tonsofmethaneperyear, tion ofliquidwater in reservoirs could pro- low-temperature surface, tian serpentiniza- floors. At a few kilometersbeneaththemar- activitythermal alsoseenonEarth’s ocean distinct fromthehigh-temperaturehydro- is and Celsius 90° to peratures ofabout40° methane. duce The process operatesattem- gen thenreactswithcarbondioxidepro- to releasing hydrogen intheprocess. The hydro- to producemineralsknown as serpentines, by also electrical activity ofatmosphericdust. oxidation, ultraviolet sunlight, and possibly which would thenbequickly destroyedby Atreya says basaltreactswithliquidwater South ( Express orGemini concentration, Methane muddle. P u b l i s h e inset d b is notsoeasily explained. headmitsthatJupiter’s troop of irregulars However, says Cuk. lites, Uranus and may have preserved thelatterplanet’s irregular satel- Asimilarpastresonancebetween from distance the planet. Saturn’s of orbits the irregular satellitestoasafe have “pumped up” between Jupiter and Saturn that occurred would past distant the in an orbital resonance According totheirnumerical simulations, Columbia in Vancouver think they’ve found mechanism. a such oftheplanet-spawningcluttereddisk. inner parts cent planetunlesssomethingbooststheirorbitswell outside the show ulations capturedsuch that objects quickly spiral nas- the into But computer sim- formed. planets the of from dust and each which ago long slowed bygas drag and captured by the rotating disksofgas Most likelythey’re asteroids, tilted orbits. eccentric, slow, in planets satellites thatswingaroundgiant the the large number of “irregular” Irregular satellitesexplained? y

)? A A o,Brett Gladmanand MatijaCukoftheUniversityBritish of Now, A S Who’sfound theright ´ nomical Society’snomical Division forSciences. Planetary for the37thmeetingof American Astro- gathered scientists 850 from 4to9September about Newtonworked on the gravitationallaws, C that methaneconcentrationsvarywidely over lion seenintheatmosphere. per bil- the concentrationsofsome10parts will goaway,says. he there’s noindicationthatthe highvalues new using far so andbettercalibrations,but reanalyzingMumma is currently the data trometer,problem a thatdoesnotoccur. blind almost MarsExpress’s sensitivespec- tions. Suchhighconcentrationswould weird” is “something abouttheseobserva- However,regions. equatorial says Atreya perbillion)insome parts 250 to (up tions and foundmuchhighermethaneconcentra- MarswithtelescopesonEarth observed AMBRIDGE So where So doesallthemethanego?Given No one really one No knows how explain to ,U.K.— hydroxyl moleculescreatedwould water up break molecules,andthe produced. Suchvoltages would kilovolts 25 permeter couldbe asstrong electric fields storms, In smalldustdevils and larger dust saysing ofdustparticles, Atreya. may lieintheelectrostaticcharg- spread outevenly. The explanation destroyedquicklytoo for the gas to itmustbe surface, the martian Center inGreenbelt,Maryland, NASA’s GoddardSpaceFlight been assumeduntilnow. is actually muchhigherthanhas that theproductionrateofmethane operating onMars,itcouldmean removal mechanism isindeed oxidize then methane.Ifthis ´ Indeed, MichaelMummaof In the medieval where city Isaac –G.S.

CREDIT: D. DUCROS/ESA; INSET: GEMINI OBSERVATORY/AURA N EWS FOCUS As for the origin of the gas, Mumma says Weirdest of all is Saturn’s thin, braided, out by “methane monsoons,” as Lunine’s he’s not sure that Atreya’s low-temperature kinky F ring, which lies just outside the main colleague Ralph Lorenz calls them after a serpentinization scenario applies to Mars. ring system. Cassini’s images show that vari- description in Arthur C. Clarke’s 1975 novel “I’d keep the biological option open,” he ous strands of the F ring are actually one and Imperial Earth. Taking into account ’s says. A definitive check on the origin of the same narrow dust ring, tightly wound into seasons, atmospheric properties, and solar methane will likely have to wait for NASA’s a spiral. This unique Mars Science Laboratory, scheduled for structure—unrelated launch in 2009. Says Mumma: “This is going to the spiral density to be a long tale.” waves that have been seen in other parts of the ring system Several New Twists (Science, 9 July 2004, p. 165)—may be for Saturn’s Rings caused by a small moonlet discovered Rough terrain. Stereoscopic images of Titan’s surface from the probe. They may appear serene and eternal, but by Cassini in an Saturn’s rings are changing, and changing eccentric orbit that appears to cross the F ring. radiation, Lorenz estimates that the “mon- fast. Over the past 25 years—the mere blink That orbit is a mystery in itself: The F ring is soons” happen every few centuries and last of an eye in planetary evolution—one partic- believed to contain many large boulders and for months. They’re like the episodic rain- ular ringlet in the innermost, tenuous part of moonlets, which would make it hard for a storms in the Arizona desert, but on a differ- the ring system moved 200 kilometers inward small satellite to survive multiple crossings. ent time scale, he says. and became one-tenth as bright. “That’s radi- Even so, the tiny object (denoted S/2004 S6) The methane in Titan’s atmosphere must cal,” says Carolyn Porco of the Space Science has been observed for almost a year. be continuously replenished because ultra- Institute in Boulder, Colorado, head of the Cassini has also spotted more bright knots violet sunlight is constantly breaking down imaging team for NASA’s Cassini spacecraft. close to the F ring, some of which are very the gas. Researchers do not yet know whether Porco’s team discovered the rapid change by elongated. “We have a hard time deciding methane has been stored in the mantle since comparing Cassini ring photos with images which of these objects are real moons and Titan’s formation or whether it is being pro- the Voyager spacecraft sent to Earth in 1980. which of them are clumps of dust,” says duced by geochemical processes beneath the “This is one of the reasons why we wanted to Porco. Even S/2004 S6 may turn out to be a surface. According to planetologist Gabriel come back,” she says. The dramatic change loose clump rather than a solid object. Future Tobie of the University of Nantes, France, suggests that this part of the ring system observations of Saturn will surely reveal new various forms of outgassing—such as cryo- could be young and rapidly developing, small satellites. Says Cassini’s project scien- volcanism, which brings water-ammonia ice although no one yet knows how to interpret tist Dennis Matson of JPL: “The complexity containing trapped methane to the surface— the observations. in the rings is just dumbfounding. We will would then release the gas into the atmos- Other ring results presented at the meeting continue to bring you excitement.” phere episodically. Indeed, radar images of are equally baffling. For instance, Cassini’s Titan’s surface obtained by NASA’s Cassini temperature measurements of the rings indicate spacecraft—Huygens’s mother ship—show that ring particles are 15° cooler on their night evidence of volcanic domes, craters, and side than on their day side. According to Linda Volcanoes,Monsoons flows. Some of the latter resemble flows on Spilker of NASA’s Jet Propulsion Laboratory Shape Titan’s Surface the slope of Mauna Loa, Hawaii. “There’s (JPL) in Pasadena, California, this means that major resurfacing going on,” says volcanolo- all particles—from a few centimeters to a few Hiking on Titan would be the ultimate gist Rosaly Lopes of NASA’s Jet Propulsion tens of meters across—rotate too slowly to extreme sport. Data from the European Laboratory in Pasadena, California. bake evenly on all sides. “We always thought Huygens lander show that the surface of the Researchers’ views about Titan’s surface that mutual collisions would lead to a wide vari- large saturnian moon is a jagged landscape have also changed since Huygens’s landing in ety of rotation rates,” says Spilker. Maybe the of extremely steep valleys, overshadowed January. During touchdown, a protruding pen- particles are fluffy and porous, she adds, which by towering ice cliffs. “It’s quite dramatic,” etrometer on the bottom of the lander first would dampen the effects of collisions. says planetary scientist Jonathan Lunine of encountered much resistance and then went the University of Arizona’s Lunar and Plan- through softer material, leading scientists to etary Laboratory in Tucson. “You would conclude that Titan was like a crème brûlée need an ice ax to scale the 30-degree with a thin, brittle crust. Now, John Zarnecki slopes.” It would be tougher than climbing a of the in , glacier, he adds: “The ground beneath your U.K., head of the Surface Science Package feet would feel more like a crumbly rock team, thinks it’s more likely that the penetrom- slope.” But at least early travelers to Titan eter hit an ice pebble similar to the ones seen in could consult the first three-dimensional Huygens’s pictures and then pushed it aside. maps of parts of the moon’s surface, which It will be a while before travel agents offer Lunine presented at the meeting. trips to Titan, but Jean-Pierre Lebreton, The Huygens lander touched down on Huygens’s project scientist at the European Titan on 14 January. During its parachuted Space Agency, hopes to go back soon. descent, it took numerous snapshots of the “Huygens has paved the way for future mis- panorama beneath. Lunine’s team has now sions to the surface of Titan,” he says. combined these into stereoscopic images of –GOVERT SCHILLING Spiral mystery. Do these objects wind up a 1.5-by-3.5-kilometer swath of terrain, Govert Schilling is an astronomy writer in

CREDITS (TOP TO CREDITS TO BOTTOM):(TOP OF ARIZONA; AND ESA/LUNAR LABORATORY/UNIVERSITY PLANETARY NASA/JPL Saturn’s F ring? showing deep, precipitous valleys carved Amersfoort, the Netherlands.

www.sciencemag.org SCIENCE VOL 309 23 SEPTEMBER 2005 1985 Published by AAAS