December 21, 2012
Meteorite Study Shows Asteroids Surfaces More Complex Than Thought
Lee Rannals for redOrbit.com - Your Universe Online
The scientists reported in the journal Science that this particular meteor is an unusual example from a rare group known as carbonaceous chondrites. Samples from this group contain some of the oldest material in the solar system.
The study of these meteorites and others like them could hold answers to unsolved mysteries about the origin of life on Earth.
"We found that this meteorite is a 'breccia,' a mixture of different rocks that accumulated at the surface of a larger asteroid, and those surfaces can be more diverse than we thought before," said co-author Denton Ebel, chair of the Division of Physical Sciences at the American Museum of Natural History.
Doppler weather radars detected falling debris traveling at about 64,000 miles per hour over the Sierra Nevada about eight months ago. Scientists performed an immediate search-and-recover mission, retrieving 77 meteorites in the process.
The fragments were in pristine condition despite entering the Earth's atmosphere at such high speeds.
"From the loud sonic boom, we quickly realized that this was an asteroid several meters in size, the biggest object to hit over land since the impact of asteroid 2008 TC3 in the north of Sudan in 2008," said lead author and meteor astronomer Peter Jenniskens of NASA Ames and SETI. "That asteroid proved to be a mixed bag of different types of meteorites, and we realized it would be very interesting to find out how diverse the Sutter's Mill meteorites were."
Several fragments were sent to laboratories around the world for analysis of the meteorite's mineralogy and structure. The Sutter's Mill meteorite was classified as a CM chondrite, C standing for carbonaceous–high in carbon content–and M standing for the group's type specimen.
The team used x-ray computed tomography (CT) to reveal the inside of a specimen without destroying it. The Museum's scanner takes more than 1,000 x-ray images of the object as it rotates inside the machine. Data collected from these x-rays are then converted by computers to form a 3D image of the specimen's interior.
"In the same way that medical tomography, called CAT scanning, is used to image the interior of the human body, CT scanning in a research laboratory allows us to obtain images of the interiors of solid objects, but with a much higher resolution," Ebel said. "This is a fundamentally important tool not just for looking at rocks but for curating them and figuring out whether anything interesting is inside."
The scans revealed that no two Sutter's Mill meteorites are the same. The meteorites contained angular pieces of different composition and density.
"This was the first time that a CM chondrite was found to be clearly a breccia," said cosmochemist Qing-Zhu Yin. "The rocky fragments came together following impacts on the parent asteroid, which implies that this meteorite originated from near its surface."
Analysis performed using different techniques at other institutions determined that the mineralogy and other geochemical features of these fragments are unexpectedly diverse and complex. They believe this suggests that the surface of the asteroid that brought the meteorites down to Earth is more complex than previously thought.
"This meteorite is special because it records many collisional processes and mixing that we, oddly, don't see very often," Ebel said. "Maybe the real question is 'why don't we see more of this?' It could be that most of the samples we've worked with in the past didn't hold up very well as they entered the atmosphere. Or that we're just seeing a small segment of what's really out there because we don't have meteorite records of what fell to the Earth thousands or millions of years ago. We still have a lot of work to do to figure out what's really going on in the asteroid belt."