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Oceans in Enceladus? Scientists can’t decide

June 24, 2009
World Science staff

Two stud­ies with con­trast­ing re­sults are leav­ing sci­en­tists scratch­ing their heads as to wheth­er there are un­der­ground oceans on En­cel­a­dus, a moon of Sat­urn.

One study sug­gests that there are; the oth­er, that there aren’t, or at least that they are deeply bur­ied if they ex­ist, ac­cord­ing to the re­search­ers in­volved.

Enceladus geysers. (Cre­dit: Cas­sini Im­ag­ing Team, SSI, JPL, ESA, NA­SA)
Under­ground oceans in En­cel­a­dus could mean the pos­si­bil­ity of life, or at least its chem­i­cal pre­cur­sors, there, ac­cord­ing to sci­en­tists.

The two re­search teams, who pub­lished their find­ings in the in the 25 June is­sue of the re­search jour­nal Na­ture, both in­ves­t­i­gated the pos­si­bil­ity of oceans on En­cel­a­dus by stu­dying so­di­um salt, or ta­ble salt, in its neigh­bor­hood.

Wa­ter va­por je­ts spew­ing from En­cel­a­dus are thought to point to sub­ter­ra­ne­ oceans if they con­tain so­di­um. If they don’t, it sug­gests the va­por is in­stead es­cap­ing from un­der­ground ice, ac­cord­ing to sci­en­tists work­ing with the Cas­si­ni mis­sion of NASA and the Eu­ro­pe­an Space Agen­cy. This is be­cause so­di­um is­n’t re­leased along with va­por in the pro­cess in which va­por es­capes di­rectly from ice, caled sub­lima­t­ion. 

One of the stud­ies, led by the Un­ivers­ity of Col­o­rad­o at Boul­der, found that there was lit­tle or no so­di­um in the je­ts, ap­par­ently damp­ing hopes for an un­der­ground ocean. 

How­ev­er, there is one way left that the find­ings could be con­sist­ent with an un­der­ground ocean: “eva­pora­t­ion from a deep cav­ern­ous ocean,” said Nich­o­las Schnei­der of the un­ivers­ity’s Lab­o­r­a­to­ry for At­mos­pher­ic and Space Phys­ics, who led the stu­dy. “Only if the eva­pora­t­ion is more ex­plo­sive would it con­tain more salt.”

In this pic­ture of slow eva­pora­t­ion from deep reser­voirs, the va­por would turn in­to a je­t at the sur­face be­cause it leaks out of small cracks in­to the vac­u­um of space, caus­ing a huge in­crease in pres­sure as it es­capes.

Some­what contradicto­ry find­ings came from Eu­ro­pe­an sci­en­tists work­ing on the Cas­si­ni mis­sion.

They did de­tect salt – not in the plumes di­rectly, but in the ice grains of Sat­urn’s E-ring, which is pri­marily be­lieved to be re­plen­ished by ma­te­ri­al from the plumes of En­cel­a­dus. The make­up of the E-ring grains was de­ter­mined through chem­i­cal anal­y­sis of thou­sands of high-speed par­t­i­cle hits reg­is­tered by Cas­si­ni. Schnei­der’s team in­stead con­ducted their stud­ies from the Keck observato­ry in Ha­waii and the An­glo-Aus­tral­ia tel­e­scope in Aus­tral­ia.

Sci­en­tists could­n’t im­me­di­ately ex­plain the dif­fer­ing re­sults, but Schnei­der did­n’t rule out that there might be some so­di­um in the plumes, while the Cas­si­ni re­search­ers said Schnei­der’s idea of slow re­lease from deep wa­ter pock­ets could work. 

“We be­lieve that the salty ma­te­ri­al deep in­side En­cel­a­dus washed out from rock at the bot­tom of a liq­uid lay­er,” said Frank Post­berg, sci­ent­ist on Cas­si­ni’s Cos­mic Dust An­a­lyz­er at the Max Planck In­sti­tute for Nu­clear Phys­ics in Hei­del­berg, Ger­ma­ny, and lead au­thor of the Cas­si­ni stu­dy.

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Two studies with contrasting results are leaving scientists scratching their heads as to whether there are underground oceans on Enceladus, a moon of Saturn. One study suggests that there are; the other, that there aren’t, or at least that they are deeply buried if they exist, according to the researchers involved. Underground oceans in Enceladus could mean the possibility of life, or at least its chemical precursors, there, according to scientists. The two research teams, who published their findings in the in the 25 June issue of the research journal Nature, both investigated the possibility of oceans on Enceladus by studying sodium salt, or table salt, in its neighborhood. Water vapor jets spewing from Enceladus are thought to point to subterranean oceans if they contain sodium. If they don’t, it suggests the vapor is instead escaping from underground ice, according to scientists working with the Cassini mission of NASA and the European Space Agency. This is because sodium isn’t released along with vapor in the process in which vapor escapes directly from ice, caled sublimation. One of the studies, led by the University of Colorado at Boulder, found that there was little or no sodium in the jets, apparently damping hopes for an underground ocean. However, there is one way left that the findings could be consistent with an underground ocean: “evaporation from a deep cavernous ocean,” said Nicholas Schneider of the university’s Laboratory for Atmospheric and Space Physics, who led the study. “Only if the evaporation is more explosive would it contain more salt.” In this picture of slow evaporation from deep reservoirs, the vapor would turn into a jet at the surface because it leaks out of small cracks into the vacuum of space, causing a huge increase in pressure as it escapes. Somewhat contradictory findings came from European scientists working on the Cassini mission. They did detect salt – not in the plumes directly, but in the ice grains of Saturn’s E-ring, which is primarily believed to be replenished by material from the plumes of Enceladus. The makeup of the E-ring grains was determined through chemical analysis of thousands of high-speed particle hits registered by Cassini. Schneider’s team instead conducted their studies from the Keck observatory in Hawaii and the Anglo-Australian telescope in Australia. Scientists couldn’t immediately explain the differing results, but Schneider didn’t rule out that there might be some sodium in the plumes, while the Cassini scientists said Schneider’s idea of slow release from deep water pockets could work. “We believe that the salty material deep inside Enceladus washed out from rock at the bottom of a liquid layer,” said Frank Postberg, scientist on Cassini’s Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, lead author of the Cassini study.