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Distant moon may have oxygen in ocean 

Oct. 9, 2009
Courtesy AAS Di­vi­sion for Plan­e­tary Sci­ences
and World Science staff

A glob­al, liq­uid ocean on Jupiter’s moon Eu­ro­pa may have plen­ty of ox­y­gen avail­a­ble to sup­port life—even animal-like or­gan­isms, a new study sug­gests.

The re­search in­di­cates Eu­ro­pa’s ocean, with twice the liq­uid wa­ter of all Earth’s oceans com­bined, could al­so have as much as 100 times more ox­y­gen than pre­vi­ously es­ti­mat­ed.

Eu­ro­pa as seen by NA­SA's Voy­ag­er 2 space­craft. (Cour­te­sy Voy­ag­er Proj­ect, JPL, NA­SA; ® C.J. Ham­il­ton)
The chances for life in Eu­ro­pa have been un­cer­tain. Eu­ro­pa’s ocean lies be­neath sev­er­al miles or kilo­me­ters of ice, which sep­a­rates it from the pro­duc­tion of ox­y­gen at the sur­face by en­er­get­ic charged par­t­i­cles, re­search­ers say. 

With­out ox­y­gen, life could con­ceivably ex­ist at hot springs in the ocean floor us­ing ex­ot­ic chem­istries, but no one knows wheth­er the right con­di­tions ex­ist.

The­re­fore a key ques­tion has been wheth­er enough ox­y­gen reaches the ocean to sup­port the sort of ox­y­gen-based met­a­bol­ism that sci­en­tists know best.

An an­swer comes from con­sid­er­ing the young age of Eu­ro­pa’s sur­face, ac­cord­ing to re­searcher Rich­ard Green­berg of the Un­ivers­ity of Ar­i­zo­na. Its ge­ol­o­gy and the paucity of im­pact craters sug­gests the top of the ice is con­tin­u­ally re-formed such that the cur­rent sur­face is only about 50 mil­lion years old, roughly one hun­dredth the age of the so­lar sys­tem, he said.

Green­berg has con­sid­ered three ge­ner­ic re­sur­fac­ing pro­cesses: grad­u­ally lay­ing fresh ma­te­ri­al on the sur­face; open­ing cracks which fill with fresh ice from be­low; and dis­rupt­ing patches of sur­face in place and re­plac­ing them with fresh ma­te­ri­al. Us­ing es­ti­mates for the pro­duc­tion of ox­i­diz­ers at the sur­face, he found that the de­liv­ery rate in­to the ocean is so fast that the ox­y­gen con­centra­t­ion could ex­ceed that of Earth oceans in only a few mil­lion years.

Green­berg is to pre­s­ent his find­ings Oct. 10 at the meet­ing of the Amer­i­can As­tro­nom­i­cal So­ci­ety’s Di­vi­sion for Plan­e­tary Sci­ences in Fa­jardo, Puerto Rico.

Green­berg said the con­centra­t­ions of ox­y­gen would be great enough to sup­port not only mi­crobes, but al­so larg­er animal-like or­gan­isms that need more ox­y­gen. The ox­y­gen supply could sup­port roughly three bil­lion kilo­grams (three mil­lion tons) of macro­fauna, as­sum­ing si­m­i­lar ox­y­gen de­mands to fish, he es­ti­mat­ed.

There would be a de­lay of a cou­ple of bil­lion years be­fore the first sur­face ox­y­gen reached the ocean, Green­berg added; this de­lay would ac­tu­ally be help­ful to fledg­ling life forms. Al­though oxy­gen is es­sen­tial for big, ener­getic org­an­isms, it also has dam­ag­ing ef­fects that can be deadly to crea­tures that haven’t yet evolved the right sort of pro­tec­tion. A si­m­i­lar de­lay in the pro­duc­tion of ox­y­gen on Earth was probably es­sen­tial for al­low­ing life to get started he­re, Green­berg not­ed.

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A global, liquid ocean on Jupiter’s moon Europa may have plenty of oxygen available to support life—even animal-like organisms, a new study suggests. The research indicates Europa’s ocean, with twice the liquid water of all Earth’s oceans combined, could also have as much as 100 times more oxygen than previously estimated. The chances for life in Europa have been uncertain. Europa’s ocean lies beneath several miles or kilometers of ice, which separates it from the production of oxygen at the surface by energetic charged particles, researchers say. Without oxygen, life could conceivably exist at hot springs in the ocean floor using exotic chemistries, but no one knows whether the right conditions exist. Therefore a key question has been whether enough oxygen reaches the ocean to support the oxygen-based metabolic process that is most familiar to scientists. An answer comes from considering the young age of Europa’s surface, according to researcher Richard Greenberg of the University of Arizona. Its geology and the paucity of impact craters suggests the top of the ice is continually re-formed such that the current surface is only about 50 million years old, roughly one hundredth the age of the solar system, he said. Greenberg has considered three generic resurfacing processes: gradually laying fresh material on the surface; opening cracks which fill with fresh ice from below; and disrupting patches of surface in place and replacing them with fresh material. Using estimates for the production of oxidizers at the surface, he found that the delivery rate into the ocean is so fast that the oxygen concentration could exceed that of Earth oceans in only a few million years. Greenberg is to present his findings Oct. 10 at the meeting of the American Astronomical Society’s Division for Planetary Sciences in Fajardo, Puerto Rico. Greenberg said the concentrations of oxygen would be great enough to support not only microbes, but also larger animal-like organisms that need more oxygen. The oxygen supply could support roughly three billion kilograms (three million tons) of macrofauna, assuming similar oxygen demands to fish, he estimated. There would be a delay of a couple of billion years before the first surface oxygen reached the ocean, Greenberg added; this delay would actually be helpful to fledgling life forms. Oxygen is hazardous, not helpful, to organisms that haven’t yet evolved protection from its damaging effects. A similar delay in the production of oxygen on Earth was probably essential for allowing life to get started here, Greenberg noted.