23. Two Clusters of Rubble Near Earth
Jean-Luc Margot
Jean-Luc Margot, Astronomy, and research colleagues made the most detailed observations ever of a binary near-Earth asteroid (NEA) using the Arecibo telescope. The asteroid (1999 KW4) is a pair of light porous clusters of rubble that circle each other as they orbit from a point closer to the sun than Mercury and then outward, occasionally passing very close to Earth. Discovered in 1999, KW4 came within 2.98 million miles of Earth in 2001, when the asteroid was observed to be binary. Using antennae at Arecibo and NASA’s Goldstone Deep Space Network, researchers for the first time had very detailed high-resolution images that allowed them to derive the shape of both asteroid components. The study involved precise tracking of an irregularly shaped binary system’s motion, which is vital to learning how the two-part asteroid formed. KW4 is also valuable for researchers studying how to mitigate the potential threat asteroids pose to Earth. KW4 is classified as a potentially hazardous asteroid (PHA), but data show that its path will not encounter Earth for at least 1,000 years. The research highlights the importance of Arecibo’s powerful radar.