Radar video of 2014 HQ124 showing the peanut-shaped asteroid rotating on its axis with a period of about 20 hours.
Every month a couple Earth-approaching asteroids fly close enough past Earth to make great targets for radar imaging. On June 8, the 1,300-foot (305-meter) asteroid 2014 HQ124, discovered in April, flew pass the planet at a distance of just 800,000 miles (1.3 million km). Hours after closest approach, astronomers used the 230-foot (70-meter) Goldstone Deep Space Network antenna California to beam radar signals at the asteroid, which obligingly reflected them back – imprinted with information about its shape, contours and rotation speed – to the 1,000-foot (305-meter) dish at Arecibo Observatory in Puerto Rico.
This ‘game of catch’ using the largest radio telescope on Earth dramatically improved the amount of detail that can be seen in radar images. A recent equipment upgrade at Arecibo enabled the two facilities to work in tandem to obtain images with this fine level of detail for the first time:
“This may be a double object, or ‘contact binary,’ consisting of two objects that form a single asteroid with a lobed shape,” said Lance Benner of NASA’s Jet Propulsion Lab. The images reveal a wealth of other features, including a puzzling pointy hill near the object’s middle, a large, dark depression and possible boulders lying on the surface.
About 1 in 6 asteroids is a contact binary. Possible scenarios for their formation include impacts that shatter larger asteroids which then reassemble into ‘rubble piles’ of busted boulders. One of the best-imaged of these rocky-road melanges is 25143 Itokawa, an asteroid visited and sampled in 2005 by the Japanese space probe Hayabusa.
For asteroids, as well as comets, radar is a powerful tool for studying the objects’ size, shape, rotation, surface features and orbits. Radar measurements of asteroid distances and velocities enable researchers to compute orbits much further into the future than if radar observations were not available.