This past April, a 100,000 pound (45,360 kg) meteorite exploded above the skies of Sutter's Mill, California. Streaking in at a speed of 64,000 miles per hour (103,000 km/hr or 28.6 km/s) — about twice the speed of typical meteorite falls — it hit with the energy of a quarter of a Hiroshima bomb, making it the biggest impact over land since a four meter-sized asteroid broke-up over Sudan four years ago. And now, after recovering and analyzing the ensuing meteorite fragments, scientists have realized that it's an incredibly ancient form of rock — one that may have brought compounds crucial for life to Earth.
After disintegrating over California in a 4-kiloton explosion, a team of scientists (including NASA researchers from Ames) scrambled to recover the fragments.
They managed to find a paltry 205 grams worth in the form of 77 pieces, but it was enough to conduct an analysis. They located the exact region where the fragments fell by using doppler weather radar — the first time this technique was used for such a purpose.
Based on photographs of the fireball, the object entered into Earth's atmosphere at an unusually low-inclined comet-like orbit that at one point reached the orbit of Mercury. Consequently, it passed closer to the sun than other recovered meteorites. But at the same time, it experienced an unusually short exposure to cosmic rays. The scientists suspect that it circled the sun three times during a single orbit of Jupiter, an important piece of insight into the object's point of origin.
The ensuing study, which was conducted by Peter Brown and colleagues at Western University and Peter Jenniskens of the SETI Institute, reveals that it was a rare carbonaceous chondrite meteorite — a so-called C-class asteroid that likely came from the Eulalia asteroid family. This is a very primitive class of asteroids that are very rarely discovered. Specifically, it's a regolith breccia that originated from near the surface of an ancient asteroid, possibly in the vicinity of Jupiter.
And importantly, the debris contained carbon. It's rocks like these, say the scientists, that contributed to the early organic chemistry on Earth — the same carbon atoms that can be found in biological matter.
Interestingly, NASA plans on sending astronauts to asteroids like these on future missions.
You can read the entire paper at Science.
Other source: SETI. Images: Photo: NASA ARC-SETI Institute/P. Jenniskens, Lisa Warren.