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October 03, 2011

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Saturn moon is snowy, forms perfect skiing powder, scientists report

Oct. 3, 2011
Courtesy of Europlanet Outreach
and World Science staff

De­tailed map­ping of Sat­urn’s moon En­cel­a­dus con­firms a fore­cast of on­go­ing snow flur­ries for that un­ique lit­tle world, scientists say. They claim that a slow build­up last­ing pro­bab­ly mil­lions of years has created a blan­ket of su­per­fine ice crys­tals as much as 100 me­ters (325 feet) deep.

This powder would likely make pe­r­fect ski­ing ma­te­ri­al, ac­cord­ing to Paul Schenk of the Lu­nar and Plan­e­tary In­sti­tute in Hous­ton, Tex­as. He pre­sented find­ings by his re­search team Oct. 3 at the 2011 joint meet­ing of the Amer­i­can As­tro­nom­i­cal So­ci­ety’s Di­vi­sion for Plan­e­tary Sci­ences and the Eu­ro­pe­an Plan­e­tary Sci­ence Con­gress in Nantes, France.

A colour im­age of the land­scape of En­cel­a­dus by NA­SA's Cas­si­ni space­craft. This ter­rain lies north of the ge­o­log­i­cal ac­tive south po­lar ridges and fea­tures a roll­ing ter­rain cross­cut by nar­row frac­tures. The large crat­er at right is 22 kilo­me­tres (14 miles) wide. (Pro­cess­ing by Paul Schenk, Lu­nar and Plan­e­tary In­sti­tute, Hous­ton)
Map­ping of glob­al colour pat­terns and mea­sure­ments of sur­face lay­er thick­nesses show that ice par­t­i­cles that form in sprays from the moon’s sur­face fall back to the ground in a pre­dict­a­ble pat­tern, Schenk ex­plained. The re­search al­so sug­gests the plumes and their heat source last for probably tens of mil­lion years at least, he added.

NASA’s Cas­si­ni space­craft mis­sion re­vealed in re­cent years that plumes of icy dust and va­por spout from En­cel­a­dus, a find­ing that “has rev­o­lu­tion­ plan­e­tary sci­ence,” said Schenk. “Ear­lier this year, we pub­lished work that showed ma­te­ri­al from En­cel­a­dus’s plumes coats the sur­faces of Sat­urn’s icy moons. Now, we’ve un­cov­ered two lines of ev­i­dence that point to thick de­posits of plume ma­te­ri­al.”

Mod­els of plume par­t­i­cle tra­jec­to­ries un­der the in­flu­ence of Sat­urn’s gra­vity sug­gest that some par­t­i­cles should re­turn to the ground in a dis­tinc­tive pat­tern. The heav­i­est build­up is pre­dicted to fall along two lon­gi­tudes on op­po­site sides of the moon. Glob­al col­or map­ping by Schenk and col­leagues shows a sym­met­ric pat­tern of blu­ish ma­te­ri­al in the very ar­eas that were pre­dicted, Schenk main­tains.

The scientific team al­so ex­am­ined de­tailed im­ages north of the plume forma­t­ion sites, with res­o­lu­tions of up to 12 me­ters or yards. The im­ages showed ev­i­dence of snow-cov­ered canyons of which the high­est are about 500 me­ters (1650 feet) deep, ac­cord­ing to Schenk and col­leagues. The snow lay­er probably grows by less than a thou­sandth of a mil­li­me­tre per year, they con­tend, so this build­up has been go­ing on for eons.

What about the sur­face it­self? Could we go ski­ing on En­cel­a­dus?

Well, if we dis­re­gard the need for bulky space suits and the prob­lem that gra­vity is only one-hundredth as strong as on Earth, “the par­t­i­cles them­selves are only a frac­tion of a mil­li­me­tre in size, roughly a mi­cron or two across, even fin­er than tal­cum pow­der,” Schenk said. “This would make for the fin­est pow­der a skier could hope for.”

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Detailed mapping of Saturn’s moon Enceladus confirms a forecast of ongoing snow flurries for that unique little world, astronomers say. The superfine ice crystals coating its surface would make perfect skiing material, according to Paul Schenk of the Lunar and Planetary Institute in Houston, Texas. He presented findings by his research team Oct. 3 at the 2011 joint meeting of the American Astronomical Society’s Division for Planetary Sciences and the European Planetary Science Congress in Nantes, France. Mapping of global colour patterns and measurements of surface layer thicknesses show that ice particles that form in sprays from the moon’s surface fall back to the ground in a predictable pattern, Schenk explained. The research also suggests the plumes and their heat source last for probably tens of million years at least, he added. NASA’s Cassini spacecraft mission revealed in recent years that plumes of icy dust and vapor spout from Enceladus, a finding that “has revolutionized planetary science,” said Schenk. “Earlier this year, we published work that showed material from Enceladus’s plumes coats the surfaces of Saturn’s icy moons. Now, we’ve uncovered two lines of evidence that point to thick deposits of plume material.” Models of plume particle trajectories under the influence of Saturn’s gravity suggest that some particles should return to the ground in a distinctive pattern. The heaviest buildup is predicted to fall along two longitudes on opposite sides of the moon. Global color mapping by Schenk and colleagues shows a globally symmetric pattern of bluish material in the very areas that were predicted, Schenk maintains. Schenk and colleagues also examined detailed images north of the plume formation sites, with resolutions of up to 12 meters or yards. The images showed evidence of snow-covered canyons of which the highest are about 500 meters (1650 feet) deep, according to Schenk and colleagues. The snow layer probably grows by less than a thousandth of a millimetre per year, they contend, so this buildup has been going on for eons. What about the surface itself? Could we go skiing on Enceladus? Well, if we disregard the need for bulky space suits and the problem that gravity is only one-hundredth as strong as on Earth, “the particles themselves are only a fraction of a millimetre in size, roughly a micron or two across, even finer than talcum powder,” Schenk said. “This would make for the finest powder a skier could hope for.”