ScienceShot: Anatomy of an Odd Asteroid

Anatomy of an Odd Asteroid

ESO (main image); JAXA (inset)

The oddly shaped, near-Earth asteroid 25143 Itokawa just got a lot weirder. When researchers analyzed how the object’s brightness changed over the course of 10 short intervals between 2001 and 2013, as measured by Earth-based telescopes, they found that the 535-meter-long cosmic peanut (inset) wasn’t rotating as expected. A detailed analysis suggested that Itokawa’s center of mass (about which the asteroid rotates) was 21 meters closer to the smaller end of the peanut than expected—a sign that the smaller end of the body, for whatever reason, is denser than the larger end. Although a shift of 21 meters doesn’t sound like much, that disparity suggests that the smaller end of the asteroid is more than 1.6 times as dense as the plumper end (main image), the researchers report today in Astronomy & Astrophysics. Previously, some researchers have proposed that Itokawa is actually two asteroids in contact with one another, a scenario strongly supported by the new results, the team contends. It’s not clear whether the odd configuration results from the merger of a two-asteroid system or merely clumps of material that fell back together after a larger asteroid was blasted apart by an immense collision. Further analyses may yield an answer, the researchers say, and they also may provide insights into how asteroids and other bodies formed during earlier days of the solar system. One more oddity revealed by the new study: Due to the peculiar shape and weight distribution of the asteroid and irregularities in the way that heat is radiated into space, the rate at which Itokawa spins is accelerating, making it rotate about 45 milliseconds faster with each passing Earth year.

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