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Ingredients of life could form over Saturn moon: study

Oct. 7, 2010
Courtesy of the University of Arizona
and World Science staff

The types of mo­le­cules nec­es­sary to build liv­ing things may have formed in the hazy at­mos­phere of Ti­tan, Sat­urn’s larg­est moon, sci­en­tists say.

The con­clu­sions come af­ter a study sim­u­lat­ing chem­i­cal pro­cesses in Ti­tan’s at­mos­phere, and check­ing for the forma­t­ion of mo­le­cules si­m­i­lar to those that com­pose life forms on Earth.

The re­search­ers said they found that mo­le­cules known as nu­cle­o­tide bas­es and ami­no acids can arise. These are com­po­nents, re­spec­tive­ly, of two key build­ing blocks of life, DNA and pro­tein molecules. DNA pro­vides the ge­net­ic code, while pro­teins make up much of the ac­tu­al struc­ture of or­gan­isms and car­ry out day-to-day chem­i­cal func­tions.

The study shows that the com­plex mo­le­cules com­pos­ing these larg­er struc­tures can arise en­tirely “in the out­er parts of an at­mos­phere,” said Uni­vers­ity of Ar­i­zo­na grad­u­ate stu­dent Sar­ah Horst, a mem­ber of the re­search team. “We don’t need liq­uid wa­ter, we don’t need a sur­face.”

The sim­ula­t­ions led to the forma­t­ion all of the five nu­cle­o­tide bas­es used by life on Earth and the two small­est ami­no acids, gly­cine and al­a­nine, said the re­search­ers, from the Uni­vers­ity of Ar­i­zo­na and oth­er in­sti­tu­tions.

In­tense radia­t­ion hits the top of Ti­tan’s thick at­mos­phere and can break apart nor­mally sta­ble molecules, mem­bers of the re­search group ex­plained. They stud­ied what hap­pens af­ter these mo­le­cules fall apart. The re­search­ers beamed radia­t­ion in­to a cham­ber con­tain­ing chem­i­cals be­lieved to rep­li­cate those in Ti­tan’s at­mos­phere, ni­tro­gen, meth­ane and car­bon mon­ox­ide. Forma­t­ion of the life-build­ing molecules, called com­plex or­gan­ic com­pounds, fol­lowed.

The re­sults not only sug­gest that Ti­tan’s at­mos­phere could con­tain mo­le­cules that might serve as the spring­board to life, but may of­fer a new per­spec­tive on the emer­gence of life on Earth, Horst and col­leagues said. For one thing, they noted, in­stead of the first in­gre­di­ents of life form­ing in a “p­ri­mor­dial soup” in the oceans, as of­ten as­sumed, they could have formed in a “p­ri­mor­dial haze” high in Earth’s at­mos­phere.

The scientists are to pre­s­ent the find­ings Oct. 7 at a meet­ing of the Amer­i­can As­tro­nom­i­cal So­ci­ety’s Di­vi­sion for Plan­e­tary Sci­ences in Pas­a­de­na, Ca­lif.

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The types of molecules necessary to build living things may have formed in the atmosphere of Titan, Saturn’s largest moon, scientists say. The conclusions come after a study simulating chemical processes in Titan’s atmosphere, and checking for the formation of molecules similar to those that compose life forms on Earth. The researchers said they demonstrated the formation of molecules known as nucleotide bases and amino acids. These are components, respectively, of two key building blocks of life, DNA and protein molecules: DNA provides the genetic code, while proteins make up much of the actual structure of organisms and carry out day-to-day chemical functions. The study shows that the complex molecules composing these larger structures can arise entirely “in the outer parts of an atmosphere,” said University of Arizona graduate student Sarah Horst, a member of the research team. “We don’t need liquid water, we don’t need a surface.” The simulations led to the formation all of the five nucleotide bases used by life on Earth and the two smallest amino acids, glycine and alanine, said the researchers, from the University of Arizona and other institutions. Intense radiation hits the top of Titan’s thick atmosphere and can break apart normally stable molecules, members of the research group explained.They studied what happens after these molecules fall apart. The researchers beamed radiation into a chamber containing chemicals believed to replicate those in Titan’s atmosphere, nitrogen, methane and carbon monoxide. Formation of the life-building molecules, called complex organic compounds, followed. The results not only suggest that Titan’s atmosphere could contain molecules that might serve as the springboard to life, but may offer a new perspective on the emergence of life on Earth as well, Horst and colleagues. Instead of the first ingredients of life forming in a “primordial soup” in the oceans, as often assumed, they could have formed in a “primordial haze” high in Earth’s atmosphere. The researchers are to present the findings Oct. 7 at a meeting of the American Astronomical Society’s Division for Planetary Sciences in Pasadena, Calif.