[meteorite-list] 123-Mile Asteroid Has Surface Water

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Wed, 28 Apr 2010 14:05:29 -0700 (MST)
Message-ID: <a9b851853813d409ec92558f5ed5c6ce.squirrel_at_webmail.lpl.arizona.edu>

Hi Sterling:

Surface water ICE! And a very think layer that must be continuously
replenished (one assumes from the interior).

Larry

> http://www.space.com/scienceastronomy/water-ice-on-asteroid-100428.html
>
> Water Ice Discovered on Asteroid for First Time
> By Clara Moskowitz
> SPACE.com Senior Writer
> 28 April 2010
>
> Water ice has been found on the surface of a nearby asteroid
> for the first time - a discovery that could help explain how
> Earth got its oceans, scientists announced Wednesday.
>
> Two teams of researchers independently verified that the
> asteroid 24 Themis - a large rock hurtling through space
> in the asteroid belt between Mars and Jupiter - is coated
> in a layer of frost.
>
> They also found that the asteroid contains organic material,
> including some molecules that might be ingredients for life.
> But scientists have not found any evidence for life itself on
> this asteroid, or anywhere else in the universe beyond Earth.
>
> While comets, which have characteristic tails and generally
> orbit farther out in the solar system, are known to have water,
> asteroids in that region were thought to be too close to the
> sun to contain water on the surface without it evaporating
> away. The largest asteroid in the solar system, Ceres, is
> thought to harbor a vast amount of frozen water, but scientists
> suspect all of it is buried beneath a rocky, dusty surface.
>
> But in this new study, researchers found concrete proof of
> water ice on the surface of 24 Themis by measuring the
> specific characteristics of sunlight bouncing off the surface
> of the asteroid. They saw the tell-tale signatures of H2O
> coating most of the surface of the 123-mile (198-km) wide
> rock.
>
> "This is the first time we've actually seen ice - literally H20 -
> on an asteroid," said one of the study leaders, Andrew Rivkin
> of Johns Hopkins University.
>
> Previously, hints that water might be present on 24 Themis
> were found in the form of hydrated minerals, which were
> thought to have formed from the reaction of water with rock.
> But this time the researchers saw the direct signature of
> water itself, he explained.
>
> Another science team, led by Humberto Campins of University
> of Central Florida, found the same thing. Both teams used the
> NASA Infrared Telescope Facility atop on Mauna Kea in Hawaii
> to make their observations, but conducted them on different nights.
>
> "Our work and their work are very nicely confirming and
> complementary," Campins said.
>
> Campins' team timed their observations so that they caught
> the asteroid at different points in its rotation, and combined
> these data to create a rough surface map, showing that not
> only is ice present on 24 Themis, but it coats much of the
> surface on all sides.
>
> "To our surprise there was water ice, there were organic molecules,
> and they were more or less evenly distributed throughout the surface,"
> Campins told SPACE.com. "We thought that was fascinating."
>
> Both teams reported their findings in the April 29 issue of the
> journal Nature.
>
> Another researcher - Henry Hsieh of Queen's University Belfast
> in the U.K., who was uninvolved in either study - noted surprise
> at the extent of ice coverage on the asteroid.
>
> "The average temperatures of asteroids (about 150-200 Kelvin)
> at this distance from the sun should cause surface ice to
> sublimate away in a matter of a few years or less, which is
> inconsistent with the billions of years that Themis is thought
> to have spent at its current location," he wrote in an
> accompanying essay in the same issue of Nature.
>
> The discovery might even provide clues about the origin of water
> on Earth.
>
> Earth has had a violent history, having been bombarded with
> space rocks throughout much of its life. In particular, a large
> rock was thought to have crashed into Earth some 4.5 billion
> years ago, knocking off a chunk that became our moon. This
> collision would have heated things up so much, any water that
> was on Earth at that point was vaporized. So how did the oceans
> arrive?
>
> Some scientists have suggested that most of it arrived via other
> asteroids that crashed into Earth later in smaller collisions. But
> for that idea to hold weight, asteroids would have to carry water.
> Comets aren't a good possibility for this scenario because the
> water they hold tends to be of a slightly different nature, with
> atoms in a different configuration, or isotope, than most of the
> water on Earth.
>
> Though the recent measurements can't tell anything about the
> isotope ratio of the water on 24 Themis, the fact that there is
> water there at all is an encouraging sign.
>
> "Our data are certainly at least consistent with the idea that
> you could bring in plenty of water form impacts," Rivkin said.
>
> If it sounds surprising that the vastness of Earth's oceans built
> up from deposits of water by asteroids, Rivkin said it isn't that
> crazy an idea.
>
> "We know that the rate of [asteroid] impacts was very high," he
> told SPACE.com. "If each impactor, each asteroid, were 20 to
> 30 percent water by weight, then that could potentially add up."
>
>
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Received on Wed 28 Apr 2010 05:05:29 PM PDT