Planetary Radar Observes 1,000th Near-Earth Asteroid Since 1968

Nearly three-quarters of all NEA radar observations have been made since NASA’s NEO Observations Program, now a part of its Planetary Defense Program, increased funding for this work 10 years ago.

The most recent asteroid to be observed by radar made its approach by Earth only a week after 2021 PJ1. Between Aug. 20 and 24, Goldstone imaged 2016 AJ193 as it passed our planet at a distance of 2.1 million miles (about 3.4 million kilometers). Although this asteroid was farther away than 2021 PJ1, its radar echoes were stronger because 2016 AJ193 is about 40 times larger, with a diameter of about three-quarters of a mile (1.3 kilometers). The radar images revealed considerable detail on the object’s surface, including ridges, small hills, flat areas, concavities, and possible boulders.

“The 2016 AJ193 approach provided an important opportunity to study the object’s properties and improve our understanding of its future motion around the Sun,” said Shantanu Naidu, a scientist at JPL who led the Aug. 22 observations of 2016 AJ193. “It has a cometary orbit, which suggests that it may be an inactive comet. But we knew little about it before this pass, other than its size and how much sunlight its surface reflects, so we planned this observing campaign years ago.”

NASA’s NEOWISE mission had previously measured 2016 AJ193’s size, but the Goldstone observations revealed more detail: It turns out to be a highly complex and interesting object that rotates with a period of 3.5 hours.