© P. Scheirich, P. JenniskensScientists have recreated what the asteroid 2008 TC3 looked like just before it slammed face-first into Earth on October 7, 2008. An artist’s illustration shows, in 12-second intervals, only the flattened part of the asteroid that faced Earth as it fell. The horizontal line at top shows actual observations of the asteroid.
Planetary scientists have reported a slew of new findings about the first asteroid ever spotted before pieces of it fell to Earth. The space rock contained a number of amino acids, had a flattened shape and appears to have been blasted off the surface of a larger body, researchers reported October 5 at the annual meeting of the American Astronomical Society's Division for Planetary Sciences.

The asteroid, 2008 TC3, first came into the limelight in 2008 when researchers spotted the body just 19 hours before it broke apart in Earth's atmosphere and crashed into northern Sudan. Planetary scientists tracked the intact asteroid as it fell to the ground as meteorites (SN: 4/25/09, p. 13).

As observed through a telescope during the last two hours of its journey to Earth, the small asteroid appeared only as a flickering point of light. But by analyzing the variations in brightness of the rock as it tumbled through space, along with information culled from fragments on the ground, Peter Scheirich of the Czech Academy of Sciences in Ondrejov and his colleagues have now reconstructed what the asteroid would have looked like up close. The space rock resembled a flattened loaf of bread, Scheirich reported.

Further analysis of the shape of the asteroid, along with estimates of the asteroid's mass and the reflectivity of the recovered meteorites, could reveal whether the rock is solid through and through or porous, like a loosely held rubble pile, he adds.

The rock entered Earth's atmosphere "like the Apollo space capsule, flat face forward," says Peter Jenniskens of the SETI Institute in Mountain View, Calif., who led an effort to recover some 300 meteorites in Sudan in October 2008.

Structures in the meteorites - pores lined with fine-grained crystals of a mineral called olivine - suggest that the asteroid was blasted off the surface of a larger rock, reported Michael Zolensky of NASA's Johnson Space Center in Houston. That means it should be relatively easy to use the properties of these meteorites to understand the properties of thousands of observed asteroids in space, which only reveal clues about their surfaces through telescope images and spectra, he says.

Other studies, also reported October 5, reveal that the meteorites contain amino acids, the building blocks of proteins, that must have come from 2008 TC3, reported Michael Callahan of NASA's Goddard Space Flight Center in Greenbelt, Md.

The meteorites belong to a rare type called ureilites, which contain microscopic diamonds. "To my knowledge this is the first report of amino acids in any ureilite-type meteorite," said Daniel Glavin of NASA-Goddard, who collaborated with Callahan and other colleagues on the analysis.

The researchers identified 18 amino acids, including alpha-aminoisobutyric acid and isovaline. Because they are uncommon on Earth, Glavin said, "it is highly likely that these two amino acids were formed in space."

"The discovery of amino acids in [2008 TC3] provides additional support for the idea that organic matter delivered by asteroids could have seeded the early Earth with the raw ingredients for life," he noted. At the same time, the presence of the amino acids is puzzling, Glavin added.

Evidence suggests that 2008 TC3 was heated to temperatures as high as 1,300˚ Celsius billions of years ago, yet amino acids are destroyed at temperatures above 500 - 600˚C, Glavin said. Other researchers, including Richard Zare, Amy Morrow and Hassan Sabbah of Stanford University in Palo Alto, Calif., reported that they had found common components of soot known as polycyclic aromatic hydrocarbons in the meteorites. This soot is interspersed with amino acids, Zare said.

"The big mystery now is how did these complex organic compounds survive such high temperatures?" notes Glavin.

One possibility is that the amino acids or their precursors were incorporated into the asteroid's parent rock during its formation and survived the heating and melting that would have occurred when the parent rock was blasted into pieces. Another possibility, he notes, is that amino acids formed inside 2008 TC3 itself much later on, after it cooled to temperatures below 500 - 600˚C.

To help settle these and other questions, Jenniskens plans to return to Sudan this December to pick up more specimens.