Spaceflight Now Home



Spaceflight Now +



Subscribe to Spaceflight Now Plus for access to our extensive video collections!
How do I sign up?
Video archive

"Chandra's Universe"

NASA's Chandra X-ray Observatory is providing new insights into the frontier of X-ray astronomy.

 Play

Station's new toilet

Space station commander Mike Fincke shows the new U.S. toilet installed aboard the complex. The astronauts are preparing the station for larger crews beginning in 2009.

 Play

The Phoenix mission

This video provides a recap of the Mars lander Phoenix and the spacecraft's mission to the frozen northern plains of the Red Planet to dig up samples of the soil and water ice.

 Play

"Debrief: Apollo 8"

This is the story of NASA's first journey in orbit around the Moon with comments on the significance of the Apollo 8 flight by several prominent Americans.

 Play

The Apollo 8 film report

This is the Manned Space Flight Film Report for the mission of Apollo 8 that orbited around the Moon on Christmas in 1968.

 Play

Next Mars rover delayed

Launch of NASA's Mars Science Laboratory will be postponed from 2009 to 2011 due to hardware development delays.

 Play

STS-126: Full coverage

More than 200 videos covering shuttle Endeavour's STS-126 mission to the space station are archived for viewing.

 Play

Daily shuttle highlights

Daily highlights movies from recent space shuttle flights can be seen here.

 Play

Become a subscriber
More video




NewsAlert



Sign up for our NewsAlert service and have the latest news in astronomy and space e-mailed direct to your desktop.

Enter your e-mail address:

Privacy note: your e-mail address will not be used for any other purpose.



Half-baked asteroids have Earth-like crust
CARNEGIE INSTITUTION NEWS RELEASE
Posted: January 7, 2009

WASHINGTON, D.C. - Asteroids are hunks of rock that orbit in the outer reaches of space, and scientists have generally assumed that their small size limited the types of rock that could form in their crusts. But two newly discovered meteorites may rewrite the book on how some asteroids form and evolve.

Researchers from the Carnegie Institution, the University of Maryland, and the University of Tennessee report in the January 8th edition of Nature that these meteorites are ancient asteroid fragments consisting of feldspar-rich rock called andesite. Similar rocks were previously known only from Earth, making these samples the first of their kind from elsewhere in the Solar System.

The two meteorites were discovered during the Antarctic Search for Meteorites (ANSMET) 2006/2007 field season in a region of the Antarctic ice known as the Graves Nunatak icefield. The light-colored meteorites, designated GRA 06128 and GRA 06129, were immediately recognized as being different from previously known meteorites.

"What is most unusual about these rocks is that they have compositions similar to Earth's andesite continental crust - what makes up the ground beneath our feet," says University of Maryland's James Day, lead author of the study. "No meteorites like this have ever been seen before."

Andesite is an igneous rock common on Earth in areas where colliding tectonic plates generate volcanoes, such as those of the Andes mountain range. The meteorites contain minerals thought to require large-scale processes such as plate tectonics to concentrate the right chemical ingredients. In view of this, some researchers had suggested that the meteorites were fragments of a planet or the Moon, not an asteroid. But analysis of the meteorites' oxygen isotopes at the Carnegie Institution's Geophysical Laboratory by Douglas Rumble ruled out that possibility.

"A number of solar system objects including parent bodies of meteorites, planets, moons, and asteroids have their own oxygen isotope signatures," says Rumble. "Just by analyzing 16O-17O-18O ratios we can tell if a meteorite came from Mars, from the Moon, or from a particular asteroid. One extensively studied parent is the asteroid 4 Vesta. In the majority of cases the actual location of the parent body is unknown, but a particular group of meteorites may be assigned to the same parent body based on the isotope ratios even if the specific location of the body isn't known. When the ratios in meteorites are plotted against one another the result is mutually parallel lines offset from one another. The GRA 06128 and GRA 06129 meteorites, and some similar ones called brachinites, plot below Earth-Moon rocks and are nearly coincident with meteorites from 4 Vesta."

The meteorites' age, more than 4.5 billion years, suggests that they formed very soon after the birth of the solar system. This makes it unlikely that they came from the crust of a differentiated planet. The chemical signature of some rare precious metals, notably osmium, in the meteorites also points to their origin on an asteroid that was not fully differentiated.

The researchers hypothesize that that the asteroid had a diameter somewhat larger than 100 kilometers, which would be sufficient to hold enough heat for the asteroid's rocks to partially, but not completely, melt. The asteroid would remain undifferentiated, but the melted portions could erupt on the asteroid's surface to form the andesitic crust.

"Our work illustrates that the formation of planet-like andesite crust has occurred by processes other than plate tectonics on solar system bodies," says Day. "Ultimately this may shed light on how evolved crust forms on planets, including Earth, during the earliest stages of their birth."

This study was supported by the NASA Cosmochemistry Program.

The Carnegie Institution has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.