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August 03, 2010

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Frosty asteroid hints at origin of oceans: scientists

April 28, 2010
Courtesy Nature
and World Science staff

Water-ice has been de­tected for the first time on an as­ter­oid, along with or­gan­ic chem­i­cals, which serve as po­ten­tial in­gre­di­ents for life forms, re­search­ers say.

The find­ings may bear on the or­i­gin of the Earth’s oceans, which may come from wa­ter on si­m­i­lar as­ter­oids, ac­cord­ing to sci­en­tists. Re­search­ers have al­so pro­posed that or­gan­ic pre­cur­sors for life may al­so come from as­ter­oids and oth­er rocky bod­ies, such as comets.

Artist's con­cep­tion of as­ter­oid 24 The­mis and two smaller rocky bod­ies that are among a num­ber be­lieved to have bro­ken off from it over a bil­lion years ago. One of the small frag­ments is in­ert and the oth­er is shown with a comet-like tail, thought to be pro­duced by wa­ter ice va­por­iz­ing away from its sur­face. (Cred­it: Ga­bri­el Pérez, Ser­vi­cio Mul­ti­Me­dia, In­sti­tuto de As­trofisica de Ca­narias, Ten­er­ife, Spain).

Two in­de­pend­ent re­search groups de­scribed the icy as­ter­oid in the April 29 is­sue of the re­search jour­nal Na­ture. In a com­men­tary ac­com­pa­nying the two pa­pers, Hen­ry Hsieh of Queen’s Uni­vers­ity Bel­fast, U.K., likened the as­ter­oid to a “liv­ing fos­sil”—a rem­nant of the early So­lar Sys­tem pre­vi­ously thought to have dis­ap­peared long ago.

The wa­ter was de­tected on 24 The­mis, one of the larg­est as­ter­oids in the main as­ter­oid belt, in­ves­ti­ga­tors said. The main as­ter­oid belt is a re­gion be­tween the or­bits of Mars and Ju­pi­ter where many such rocky bod­ies or­bit the Sun.

The de­tec­tions were made us­ing an in­fra­red tel­e­scope on Hawai­i’s Mau­na Kea moun­tain, tak­ing mea­sure­ments of the spec­trum of light re­flected from the as­ter­oid. Such a tech­nique can re­veal spe­cif­ic chem­i­cals, be­cause these can ab­sorb light at spe­cif­ic col­ors, re­mov­ing them from the spec­trum. The re­sult, de­pend­ing on the com­pound, is a char­ac­ter­is­tic sig­na­ture of thin black lines that in­ter­rupt an oth­erwise con­tin­u­ous spec­trum from red to vi­o­let.

In one pa­per in Na­ture, An­drew Rivkin of Johns Hop­kins Uni­vers­ity in Lau­rel, Md. and Josh­ua Em­ery of the Uni­vers­ity of Ten­nes­see, Knox­ville, de­scribed an ab­sorp­tion fea­ture in the spec­trum that they said can be ex­plained by an ex­tremely thin lay­er of frost, mixed with carbon-containing ma­te­ri­al. 

In a sec­ond pa­per, the Uni­vers­ity of Cen­tral Flori­da’s Hum­berto Campins and col­leagues reached the same con­clu­sion. They added that the spec­trum’s con­stant ap­pear­ance as the as­ter­oid ro­tates sug­gests that ice and or­gan­ic ma­te­ri­al are spread widely across the as­ter­oid sur­face.

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Water-ice has been detected for the first time on an asteroid, along with organic chemicals, which serve as potential ingredients for life forms, researchers say.. The findings may bear on the origin of the Earth’s oceans, which may come from water on similar asteroids, according to scientists. Researchers have also proposed that organic precursors for life may also come from asteroids and other rocky bodies, such as comets. Two independent research groups described the icy asteroid in the April 29 issue of the research journal Nature. In a commentary accompanying the two papers, Henry Hsieh of Queen’s University Belfast, U.K., likened the asteroid to a “living fossil”—a remnant of the early Solar System previously thought to have disappeared long ago. The water was detected on 24 Themis, one of the largest asteroids in the main asteroid belt, investigators said. The main asteroid belt is a region between the orbits of Mars and Jupiter where many of the rocky bodies orbit the Sun. The detections were made using an infrared telescope on Hawaii’s Mauna Kea, taking measurements of the spectrum of light reflected from the asteroid. Such a technique can reveal specific chemicals, because these can absorb light at specific colors, removing them from the spectrum. The result, depending on the compound, is a characteristic signature of thin black lines that interrupt an otherwise continuous spectrum from red to violet. In one research paper, Andrew Rivkin of Johns Hopkins University in Laurel, Md. and Joshua Emery of the University of Tennessee, Knoxville, described an absorption feature in the spectrum that they said can be explained by an extremely thin layer of frost, mixed with carbon-containing material. In a second paper, the University of Central Florida’s Humberto Campins and colleagues reached the same conclusion. They added that the spectrum’s constant appearance as the asteroid rotates suggests that ice and organic material are spread widely across the asteroid surface.