"Long before it's in the papers"
May 07, 2015


Chemical process in Saturn moon could help spark life, scientists say

May 7, 2015
Courtesy of the Carnegie Institution
and World Science staff

Life-friendly chem­i­cal pro­cesses may be un­fold­ing with­in Sat­urn’s moon En­cel­a­dus, ac­cord­ing to a new study of wa­ter from that moon.

The sixth planet’s sixth largest moon, Enceladus is thought to have a liq­uid wa­ter ocean be­neath its icy sur­face. That would ex­plain geyser-like plumes seen jet­ting out of the moon. And liq­uid wa­ter could mean life.

The sci­en­tists be­hind the study de­vel­oped a chem­i­cal mod­el based on da­ta from ice grains and gas­es in En­cel­a­dus’ plume gath­ered by the Cas­si­ni space­craft, a NASA and the Eu­ro­pe­an Space Agen­cy mis­sion.

Cas­si­ni gath­ered the da­ta us­ing mass spec­trom­e­try, which meas­ures the amounts and types of chem­i­cals in a sam­ple by adding an elec­tri­cal charge to them. This in­di­rectly re­veals the weight of in­di­vid­ual molecules. The pro­cess can fur­ther yield in­forma­t­ion about ac­id­ity or al­so al­ka­lin­ity, the op­po­site of ac­id­ity.

The find­ings are pub­lished in the jour­nal Geochim­ica et Cos­mochim­ica Ac­ta.

The mod­el sug­gests the plume, and there­fore the ocean, is salty, con­tain­ing the same type of salt as Earth’s oceans, so­di­um chlo­ride. It al­so points to high al­ka­lin­ity, with a pH—a meas­ure of ac­id­ity or al­ka­lin­ity—of about 11 or 12, si­m­i­lar to that of glass-cleaning am­mo­nia so­lu­tions.

The wa­ter al­so has plen­ti­ful amounts of the com­pound so­di­um car­bon­ate, the find­ings sug­gest. That would make it si­m­i­lar to “soda lakes” on Earth such as Mon­o Lake in Cal­i­for­nia or Lake Ma­g­adi in Ken­ya, ac­cord­ing to the sci­en­tists, who call it a “soda ocean.”

The mod­el al­so sug­gests the al­ka­lin­ity is due an un­derwa­ter geochem­i­cal pro­cess called ser­pentin­iz­a­tion. On Earth, this oc­curs when cer­tain kinds of me­tal­lic rocks known as “ul­tra­ba­sic” or “ul­tra­mafic” come up to the ocean floor from the man­tle, deep un­der­ground, and in­ter­act with the wa­ter molecules. This con­verts the rocks in­to new min­er­als, in­clud­ing one called ser­pentine, and makes the wa­ter more al­ka­line.

On En­cel­a­dus, ser­pentin­iz­a­tion would oc­cur when ocean wa­ter cir­cu­lates through a rocky co­re at the bot­tom of its ocean, the sci­en­tists said.

“Why is ser­pentin­iz­a­tion of such great in­ter­est? Be­cause the re­ac­tion be­tween the me­tal­lic rocks and the ocean wa­ter al­so pro­duces mo­lec­u­lar hy­dro­gen (H2), which pro­vides a source of chem­i­cal en­er­gy that is es­sen­tial for sup­port­ing a deep bi­o­sphere in the ab­sence of sun­light in­side moons and plan­ets,” ex­plained Chris­to­pher Glein of the Car­ne­gie In­sti­tu­tion for Sci­ence in Wash­ing­ton, D.C., a co-author of the stu­dy.

“Molec­u­lar hy­dro­gen can both drive the forma­t­ion of or­gan­ic com­pounds like ami­no ac­ids that may lead to the or­i­gin of life, and serve as food for mi­cro­bi­al life such as methane-producing or­gan­isms. As such, ser­pentin­iz­a­tion pro­vides a link be­tween ge­o­log­i­cal pro­cesses and bi­o­log­i­cal pro­cesses. The dis­cov­ery of ser­pentin­iz­a­tion makes En­cel­a­dus an even more prom­is­ing can­di­date for a sep­a­rate gen­e­sis of life.”

The tech­nique of the study may be use­ful for search­ing for hab­it­a­ble con­di­tions in oth­er icy worlds, such as Jupiter’s moon Eu­ro­pa, he added.

“This kind of syn­er­gy be­tween ob­serva­t­ions and mod­eling can tell us a great deal about the geochem­i­cal pro­cesses oc­curring on a far­a­way ce­les­tial ob­ject, thus open­ing the door to an ex­cit­ing new era of chem­i­cal oceanography in the so­lar sys­tem and be­yond.” Glein said.

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Life-friendly chemical processes may be unfolding within Saturn’s moon Enceladus, according to a new study that looks at characteristics of its water. The moon is thought to have a liquid water ocean beneath its icy surface, which would explain geyser-like plumes seen jetting out of the moon. And liquid water could mean life. The scientists behind the new study developed a chemical model based on data from ice grains and gases in Enceladus’ plume gathered by the Cassini spacecraft, a NASA and the European Space Agency mission. Cassini gathered the data using mass spectrometry, which measures the amounts and types of chemicals in a sample by adding an electrical charge to them. This indirectly reveals the weight of individual molecules. The process can further yield information about acidity or also alkalinity, the opposite of acidity. The findings are published in the journal Geochimica et Cosmochimica Acta. The model suggests the plume, and therefore the ocean, is salty, containing the same type of salt as Earth’s oceans, sodium chloride. It also points to high alkalinity, with a pH–a measure of acidity or alkalinity–of about 11 or 12, similar to that of glass-cleaning ammonia solutions. The water also has plentiful amounts of the compound sodium carbonate, the findings suggest. That would make it similar to “soda lakes” on Earth such as Mono Lake in California or Lake Magadi in Kenya, according to the scientists, who call it a “soda ocean.” The model also suggests the alkalinity is due an underwater geochemical process called serpentinization. On Earth, it occurs when certain kinds of metallic rocks known as “ultrabasic” or “ultramafic” come up to the ocean floor from the mantle, deep underground, and interact with the water molecules. This converts the rocks into new minerals, including one called serpentine, and makes the water more alkaline. On Enceladus, serpentinization would occur when ocean water circulates through a rocky core at the bottom of its ocean, the scientists said. “Why is serpentinization of such great interest? Because the reaction between the metallic rocks and the ocean water also produces molecular hydrogen (H2), which provides a source of chemical energy that is essential for supporting a deep biosphere in the absence of sunlight inside moons and planets,” explained Christopher Glein of the Carnegie Institution for Science in Washington, D.C., a co-author of the study. “Molecular hydrogen can both drive the formation of organic compounds like amino acids that may lead to the origin of life, and serve as food for microbial life such as methane-producing organisms. As such, serpentinization provides a link between geological processes and biological processes. The discovery of serpentinization makes Enceladus an even more promising candidate for a separate genesis of life.” The technique may be useful for searching for habitable conditions in other icy worlds, such as Jupiter’s moon Europa, he added. “This kind of synergy between observations and modeling can tell us a great deal about the geochemical processes occurring on a faraway celestial object, thus opening the door to an exciting new era of chemical oceanography in the solar system and beyond.” Glein said.