NASA’s Lucy spacecraft made history on April 20th by revealing an asteroid that was once two smaller pieces conjoined into a larger whole. The spacecraft flew within 1,000 kilometers (600 miles) of asteroid 52246 Donaldjohanson, capturing stunning images of its surface.
The asteroid is named after American paleoanthropologist Donald Johanson, who discovered the “Lucy” hominid fossil in 1974. Scientists were unsure what to expect from the spacecraft’s photos, but Lucy perfectly framed the asteroid as it flew past, revealing a heavily cratered and lumpy world with two prominent lobes conjoined at a relatively narrow neck.
The surface of Donaldjohanson is rocky and carbon-rich, covered with craters of varying crispness. The asteroid also features linear features in the neck area that might have resulted from landslides. This contact-binary shape is common among small bodies in the solar system.
One surprise discovery was that Donaldjohanson is much larger than initially estimated from Earth, measuring about 8 kilometers (5 miles) long at its widest point. The asteroid’s slow rotation period of 251 hours made it difficult to capture clear images, but Lucy’s data will help scientists better understand this unique asteroid.
The spacecraft’s autonomous target-tracking system successfully tracked Donaldjohanson for 30 minutes before the close approach, capturing detailed data with its instruments. This marks a significant upgrade in targeting long-focal-length imagers and demonstrates Lucy’s capability to make the most of upcoming Trojan asteroid encounters without wasting precious encounter time and data volume.
Lucy’s next encounter will be with its first Trojan asteroid, 3548 Eurybates-Queta, in August 2027.
Source: https://skyandtelescope.org/astronomy-news/meet-asteroid-donaldjohanson