These grainy radio echoes of a weirdly-shaped asteroid tumbling through a close approach of our home planet are oddly hypnotizing.
Asteroid 1999 JD6 is a contact binary: two distinct lobes stuck together. From previous observations, we know the asteroid tumbles through a complete revolution about once every 7.5 hours. The asteroid recently made a relatively close approach of Earth, passing within 7.2 million kilometers (4.5 million miles) late on July 24, 2015. At roughly 19 times the Earth-moon distance, that’s comfortably far enough away to not ruffle the most easily-alarmed catastrophists.
Asteroid 1999 JD6 imaged by bistatic radio echoes during a close approach on July 24, 2015. Image credit: NASA/JPL-Caltech/GSSR
It’s large for a Near Earth Object, elongated to 2 kilometers (1.2 miles) along its longest axis. This size may be a bit off — one of the reasons researchers are pleased they were able to take these radar echoes of 1999 JD6 is because the size-estimates from infrared observations have been inconsistent. About 15% of near-Earth asteroids over 180 meters (600 feet) in diameter have this sort of strange, peanut-esque shape.
The images are radio echoes captured by pairing the 70-meter Deep Space Network antenna in Goldstone, California with the 100-meter Green Bank Telescope in West Virginia. The Goldstone antenna generates a radar pulse which bounces off the asteroid, and the reflections are received by the Green Bank Telescope. These bistatic observations allow for greatly increased detail in radar images, resulting in a resolution fine enough to reveal features just 7.5 meters (25 feet) across. Data was collected through a full revolution—7.5 hours.
Asteroid 1999 JD6 will make another close-ish approach in forty years, passing by Earth at roughly the same distance in 2054.
Top image: Radar echoes of 1999 JD6 during a close approach. Credit: NASA/JPL/GSRR/Mika McKinnon