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Could space dust have brought life’s ingredients to Earth?

Jan. 24, 2014
Courtesy of University of Hawaii - SOEST
and World Science staff

Space dust br­ings wa­ter and or­gan­ic mo­le­cules to Earth and si­m­i­lar rocky plan­ets, a study has found, and may have helped cre­ate life.

“In­ter­plan­e­tary dust” from comets, as­ter­oids, and left­o­ver de­bris from the birth of the so­lar sys­tem, con­tin­u­ally rains on­to Earth. These par­t­i­cles are bom­barded by so­lar wind, mainly charged hy­dro­gen atoms. This bom­bard­ment knocks atoms out of or­der in the ma­te­ri­al that makes up the dust, called sil­i­cate min­er­al crys­tal, the re­search­ers said. That leaves be­hind ox­y­gen that’s more avail­a­ble to chem­ic­ally re­act with hy­dro­gen, for ex­am­ple, to make wa­ter.

This artist's con­cep­tion shows sur­faces of ti­ny space dust par­t­i­cles be­ing "weathered" by so­lar wind, caus­ing rims to form on their sur­faces. Ti­ny water-filled pouches are found to form there (blue). (Cred­it: John Brad­ley, UH SOEST/ LLNL )


“It is a thrill­ing pos­sibil­ity that this in­flux of dust has acted as a con­tin­u­ous rain­fall of lit­tle re­action ves­sels con­tain­ing both the wa­ter and or­gan­ics needed for the even­tu­al or­i­gin of life on Earth and pos­sibly Mars,” said Hope Ishii of the Uni­vers­ity of Hawaii-Manoa and co-author of the stu­dy. The pro­cess could hap­pen in al­most any plan­e­tary sys­tem, he added.

Air­less bod­ies in space such as as­ter­oids and the Moon, with abun­dant sil­i­cate min­er­als, are con­stantly be­ing ex­posed to this so­lar wind that can gen­er­ate wa­ter, the re­search­ers added; that may ex­plain why ice is de­tected in per­ma­nently shad­owed re­gions of the Moon.

More­o­ver, the dust, es­pe­cially “from prim­i­tive as­ter­oids and comets, has long been known to car­ry or­gan­ic car­bon spe­cies [chem­icals] that sur­vive en­ter­ing the Earth’s at­mos­phere, and we have now dem­on­strat­ed that it al­so car­ries so­lar-wind-gen­er­ated wa­ter. So we have shown for the first time that wa­ter and or­gan­ics can be de­liv­ered to­geth­er.”

It’s been known since the Apollo era, when as­tro­nauts brought back rocks and soil from the Moon, that so­lar wind causes the chem­ical make­up of the dust’s sur­face lay­er to change. So the idea that the so­lar wind might pro­duce wa­ter has been around since then, but wheth­er it ac­tu­ally does so has been de­bat­ed. The rea­sons for the un­cer­tain­ty, Ishi­i’s group said, are that the amount of wa­ter pro­duced is small and con­fined to small ar­eas so that old­er an­a­lyt­i­cal tech­niques could­n’t con­firm its pres­ence.

Us­ing a newer technology, the trans­mis­sion elec­tron mi­cro­scope, they de­tected such wa­ter in the “space-weathered” rims on sil­i­cate min­er­als in interplan­e­tary dust par­t­i­cles. 

“In no way do we sug­gest that it was suf­fi­cient to form oceans,” said Ishii. “How­ever, the rel­e­vance of our work is not the or­i­gin of the Earth’s oceans but that we have shown con­tin­u­ous, co-delivery of wa­ter and or­gan­ics in­ti­mately in­ter­mixed.”

The study is published in the journal Pro­ceed­ings of the Nat­ion­al Aca­demy of Sci­ences
.

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Space dust could bring water and organic molecules to Earth and similar rocky planets, a study proposes, possibly helping to create life. “Interplanetary dust” from comets, asteroids, and leftover debris from the birth of the solar system, continually rains onto Earth. These particles are bombarded by solar wind, mainly charged hydrogen atoms. This bombardment knocks atoms out of order in the material that makes up the dust, called silicate mineral crystal, the researchers said. That leaves behind oxygen that’s more available to chemically react with hydrogen, for example, to make water. “It is a thrilling possibility that this influx of dust has acted as a continuous rainfall of little reaction vessels containing both the water and organics needed for the eventual origin of life on Earth and possibly Mars,” said Hope Ishii of the University of Hawaii-Manoa and co-author of the study. The process could happen in almost any planetary system, he added. Airless bodies in space such as asteroids and the Moon, with abundant silicate minerals, are constantly being exposed to this solar wind that can generate water, the researchers added; that may explain why ice is detected in permanently shadowed regions of the Moon. Moreover, the dust, especially “from primitive asteroids and comets, has long been known to carry organic carbon species [chemicals] that survive entering the Earth’s atmosphere, and we have now demonstrated that it also carries solar-wind-generated water. So we have shown for the first time that water and organics can be delivered together.” It has been known since the Apollo-era, when astronauts brought back rocks and soil from the Moon, that solar wind causes the chemical makeup of the dust’s surface layer to change. So the idea that solar wind irradiation might produce water-species has been around since then, but whether it actually does produce water has been debated. The reasons for the uncertainty, Ishii’s group said, are that the amount of water produced is small and confined to small areas so that older analytical techniques couldn’t confirm its presence. Using a newer transmission electron microscope, they detected such water in the “space-weathered” rims on silicate minerals in interplanetary dust particles. “In no way do we suggest that it was sufficient to form oceans,” said Ishii. “However, the relevance of our work is not the origin of the Earth’s oceans but that we have shown continuous, co-delivery of water and organics intimately intermixed.”