The bizzare world of Itokawa as seen from Hayabusa.
Asteroids are probably the most intriguing bodies in our solar system. More than just errant chucks of rock, these tiny worlds may hold the key to early planetary accretion. Several mysteries about these bodies persist; are they single slabs of rock, or loosely held together rubble piles? The question may be more than just an academic one, especially if we want to move one of these celestial missiles headed our way. Now, researcher Rick Binzel of MIT has noted a curious factor about many Near Earth Asteroids (NEA’s); nearly all which have experienced close passages near the Earth have seemed to undergo a spectral change. Specifically, the study looked at simulations of the orbits of 95 NEAs. Most are of the S-type, showing a reddish, sun burnt spectrum indicative of solar wind blasting for several million years. About 20, however, show a Q-type resurfacing, as if they had been “freshened up” somehow. Q-type asteroids are of the same spectral class as ordinary chondrite meteorites found on Earth, and are almost never observed in the main asteroid belt. Tracing back their orbits, all 20 show evidence of passages closer to the Earth than our Moon sometime in their history. Scientist Pierre Vernazza of the European Space Agency estimates that asteroids can be reddened by solar wind exposure in about one million years. Looking at asteroids such as 25143 Itokawa imaged by the Japanese Space Agencies’ Hayabusa spacecraft, one can easily imagine such a loose collection of rock experiencing massive landslides as it passes the massive Earth. Such an event may even splinter the main body, as happened to comet Shoemaker-Levy 9 in 1992 when it was torn apart and ultimately impacted Jupiter. And we have an unprecedented opportunity to study an NEA in 2029, when asteroid 99942 Apophis swings by Earth at a distance of about 20,000 miles above our surface. “My vision is that we would have (Apophis) all wired up and monitored so that we can listen to it creak and groan as it flies by,” says Binzel. Knowing what kind of shifting terrain they face might also be of vital importance to future visiting astronauts. A mission to such a body was stated by president Obama in a recent address given at the Kennedy Space Center. Clearly, these bodies are of unparalleled interest… all eyes will be on the Australian desert on June 13th of this year as Hayabusa returns to Earth. Did it successfully grab a sample of an NEA? Researchers won’t know for sure until they have the sample return canister in hand!