The asteroid that crashed into the Nubian desert in the fall of 2008 turns out to be more interesting than we first realized. You’ll recall that the 59-ton object was first detected by the Catalina Sky Survey (another reassuring instance of the CSS doing its job, as discussed in a recent post). That allowed astronomers to track the asteroid immediately before its plunge into the Earth’s atmosphere, a first for this kind of observation. In addition, it was possible to create a search grid that Peter Jenniskens (NASA Ames) was able to use in guiding a recovery team in the Sudanese desert. Four expeditions later, 600 meteorite fragments are now at our disposal. This short film was made during the effort, giving an idea of conditions in the search field.
A close examination of these fragments reveals the interesting fact that the asteroid (2008 TC3) contained at least ten different kinds of meteorites, some containing chemicals that form life’s building blocks. Researchers have identified amino acids and polycyclic aromatic hydrocarbons (PAHs), the latter being complex organic molecules that are widely distributed in the galaxy. But the fact that 2008 TC3 was unusual became obvious long before its fragments made their way into a laboratory. “ Right from the start,” says Muawia Shaddad (University of Khartoum), “the students were surprised to find so much diversity in meteorite texture and hue.”
Growth After an Ancient Collision
Shaddad led the search effort, which included 150 students from the university. Approximately 23 pounds of asteroid debris were recovered by the team, and scientists have been able to identify most of the fragments as ureilites, a kind of meteorite so uncommon that fewer than 10 of the nearly 1,000 known meteorites fall into this category. The team was also able to identify a mixed-composition, or polymict ureilite. The remaining fragments are similar to the far more common kind of meteorites called chondrites, but it’s the ureilite fragments that have center stage at the moment. They contain varying amounts of the minerals olivine and pyroxene.
Researchers at the Carnegie Institute of Washington have found that the olivine and pyroxene have the full range of oxygen atom signatures detected in previous ureilites. This argues for all known ureilites having an origin in a common source. Such a parent body might have been fragmented in a collision 4.5 billion years ago that caused iron-rich minerals to smelt into metallic iron, while the olivine and pyroxene failed to melt, allowing the oxygen atoms in them to remain in the same arrangement as when the object first formed. 2008 TC3 was, then, one of a number of fragments of the parent body that underwent a series of subsequent collisions and impacts.
These later impacts account for the incorporation of non-ureilite types of meteorites in the asteroid, an indication that mixing and reassembly may not be unusual among asteroids. Says Jenniskens:
“Asteroids have just become a lot more interesting. We were surprised to find that not all of the meteorites we recovered were the same, even though we are certain they came from the same asteroid.”
Interesting indeed, and a reminder that our knowledge of asteroids down to their basic composition is more than a little incomplete. Asteroids are intriguing objects in their own right — we know they could play a role in providing raw materials in the development of a future infrastructure in space — but we also need to know enough about them to know how they would behave if it ever becomes necessary to nudge one out of an Earth-crossing trajectory. Along the way, gaining much good data about the early Solar System is a not inconsiderable bonus.
A series of papers flow from this work, but see Jenniskens and Shaddad, “2008 TC3: The small asteroid with an impact,” Meteoritics & Planetary Science Vol. 45, Issue 10-11, pp. 1553-1556 (abstract). Links to the other papers on 2008 TC3 in the same journal issue are here. An excellent SETI Institute talk by Jenniskens is also available on YouTube.