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Science Friday
Ice confirmed on an asteroid
Frozen water leaves its signature over the entire surface of the asteroid 24 Themis
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FAJARDO, Puerto Rico — Space rocks may be dead as doornails but some contain ingredients that could have given life on Earth a foothold.

Planetary scientists reported October 7 that they have, for the first time, confirmed that an asteroid contains frozen water on its surface. Evidence of water-ice, along with organic compounds, on the surface of the asteroid 24 Themis supports the theory that asteroids brought both water and organic compounds to the early Earth, helping lay the foundation for life on the planet.

Humberto Campins of the University of Central Florida in Orlando and his colleagues recorded spectra of the asteroid 24 Themis over a seven-hour period, corresponding to 84 percent of the rotational period of the spinning rock. The spectra, taken with NASA’s Infrared Telescope Facility on Hawaii’s Mauna Kea, revealed the consistent presence of frozen water as different parts of the asteroid’s surface came into view, Campins reported at the annual meeting of the American Astronomical Society’s Division for Planetary Sciences.

The finding corroborates earlier observations (SN Online: 7/18/08) of the same asteroid by Andrew S. Rivkin of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., and Joshua Emery of the University of Tennessee in Knoxville, who also used the Infrared Telescope Facility. Over several years, Rivkin and Emery had found evidence of frozen water in single spots on 24 Themis but had not studied the asteroid as it made one entire rotation. Together, the two teams’ findings reveal that the asteroid’s entire surface is coated with frozen water, Campins says.

The analyses of the sunlight reflected off the asteroid also show that organic compounds are widespread on the surface, he added, including polycyclic aromatic hydrocarbons, CH2 and CH3.

At the asteroid’s average distance from the sun — 3.2 times Earth’s distance to the sun — frozen water on the surface would readily vaporize, noted Campins. That means the ice must be continually replenished, possibly by a reservoir of frozen water within the rock, he speculates.

One possibility is that ice lies buried several meters below the surface of the roughly 160-kilometer-wide asteroid and makes its way to the top when the asteroid is pummeled by space debris. Norbert Schörghofer of the University of Hawaii at Manoa proposed last year that ice can persist for billions of years just below the surface of a dusty space rock if the asteroid’s surface temperature is less than about 145 kelvins. The temperature of 24 Themis lies in that range.

The presence of frozen water on 24 Themis also suggests that some asteroids resemble comets, becoming active suddenly and venting material into space when pockets of ice vaporize, Campins noted.


Found in: Atom & Cosmos

Comments 5
  • This discovery confirms cometary paradigm of origin of planets and stars from interstellar environment (dust and gas). This approach was shown in following papers [Link was removed] [Link was removed] [Link was removed]
    Indeed practically all asteriods are wizened remainders of comets, captured by Solar System from Galaxy, basically from its arms.
    Karim Khaidarov Karim Khaidarov
    Oct. 10, 2009 at 1:06am
  • Actually, Mr. Khaidarov, while you are no doubt correct that at least some Asteroids are of cometary origin; most of them are probably the remains of a planet (or two) that were either broken up through collisions, or through their gravitational tug-o-war between Jupiter and Mars.
    After all, what would the differentiated core material of a planetoid that was completly broken up in such a manner look like, if not an M-class Asteroid? One would imagine that the inner core would end up as a 'pure nickel-iron' remnant (like the minority of metalic meteorites), while the outter core - which would be somewhat mixed with lower mantel material - would be nickel-iron with inclusions of mantle-type material (like the 'mixed' metalic meteorites that have peridot inclusions).
    If this argument does not satisfy; then tell me, based on our observations - which have proven Whipples 'dirty snowball' hypothesis, nicely - how could the M-class Asteroids be remnants of Comets? We've never seen a Comet - or any other Oort Cloud/Kuiper Belt Objects, for that matter - that are anything like them!
    James Staples James Staples
    Oct. 13, 2009 at 3:45pm
  • Dear Mr. Staples,
    You wrote:
    "After all, what would the differentiated core material of a planetoid that was completly broken up in such a manner look like, if not an M-class Asteroid?"
    Indeed, we must consider the origin of asteroids in all its difficulty.
    Really, the evolution of cometary bodies is difficult path of collisions during very long time.
    Comets are not internal objects of Solar System.
    They come to our planetary system from the deep space.
    Its life time is about trillion years, and its fate fases every comet with different fragmens of other decayed celestial bodies.
    Comets are collectors of interstellar material.
    In those collections there are many reminders of rocky parts of ruined exoplanets.
    For seeing detailed information I reference readers to my papers again.
    Karim Khaidarov Karim Khaidarov
    Nov. 14, 2009 at 12:16am

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    m9bnat m9bnat m9bnat m9bnat
    Jan. 3, 2010 at 10:13pm

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    m9bnat m9bnat m9bnat m9bnat
    Jan. 5, 2010 at 7:21pm
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Suggested Reading :
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  • Cowen, R. 2008. Resident asteroids sprout comet-like dust tails
    Science News Online (July 17) Available to subscribers: [Go to]

    Cowen, R. 2006. Ice among the rocks. Science News 169(April 22):252. Available to subscribers: [Go to]

    Cowen, R. 2005. Icy world found inside asteroid. Science News 168(Sept. 25):206. Available to subscribers: [Go to]

    For more information about the AAS Division for Planetary Sciences 2009 meeting, click [Go to] and for a searchable full scientific program click [Go to]
Citations & References :
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  • Campins, H., et al. 2009. Confirming water ice on the surface of asteroid 24 Themis. American Astronomical Society’s Division for Planetary Sciences meeting. Oct. 4–9. Fajardo, Puerto Rico. [Go to]
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