Look! NASA’s Lucy Mission Stumbled Upon An Asteroid With Planet-Like Features

Dinkinesh is a tough half-mile-wide rock.

NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab/Brian May/Claudia Manzoni

NASA's Lucy mission, which is a first of its kind mission to study a population of mysterious relics from the formation of the Solar System near Jupiter. And, as mission photos suggest, it’s not always about the destination, but the rocky encounters you make along the way.

The Lucy mission, named after the famous 3 million year old hominid fossil, is slated to visit the Trojans, a swarm of asteroids stuck in Jupiter’s orbit that may be relics of the Solar System’s formation. But the spacecraft made a pitstop at asteroid Dinkinesh on November 1, 2023 for what was meant to be a simple test subject for the spacecraft's navigational systems.

The asteroid, however, turned out to have plenty of science to offer, including new information about how planets form, according to a new study published Wednesday in the journal Nature. Dinkinesh, and its surprise mini-moon Selam, might also contain clues about how the planets formed billions of years ago, the study reveals.

Panels a, b, and c each show stereographic image pairs of the asteroid Dinkinesh that NASA’s Lucy Spacecraft’s took, using its L’LORRI instrument. The images were snapped in the minutes around closest approach on November 1, 2023.

The yellow dots indicate the trough, and the rose dots show the ridge features.


Hello Dinkinesh

Dinkinesh is a rough half-mile-wide rock.

Lucy’s images show that Dinkinesh, located in the inner edge of the main asteroid belt between Mars and Jupiter, has a trough and a ridge, and is shaped like a spinning top.

Researchers think the ridge formed when a large chunk of rock dislodged from Dinkinesh. When the rock got knocked out, it broke into tiny pieces. These bits then settled to form the ridge. Some rock pieces might also have been lofted into space and then rained back down to add to the ridge.

“Basically, the planets formed when zillions of smaller objects orbiting the Sun, like asteroids, ran into each other. How objects behave when they hit each other, whether they break apart or stick together, has a lot to do with their strength and internal structure,” Lucy mission principal investigator Hal Levison said in the announcement.

Dinkinesh's terrain suggests it has a sturdy interior. This would have been an essential trait during the formation of the planets billions of years ago. The researchers think that the rock dislodged when an earthquake-like event occurred. During these types of events, there's a gradual buildup of stress that culminates as a swift release. If a celestial body experiences this type of event, that suggests it has a compact composition. If Dinkinesh's rocks were more loosely gathered together, the stress may not have built up, but instead, created gradual changes to the terrain, similar to the way a sand dune shape shifts.

The dislodged rock event could also explain how Dinkinesh’s tiny moon, Selam, formed. Over millions of years, the Sun’s thermal radiation caused Dinkinesh’s spin to accelerate. This created a centrifugal force. As material pooled near the center, or flew off into nearby space, Selam gained its raw ingredients.

In keeping with the moniker theme of the Lucy mission, Selam is a greeting meaning “peace” in the Amharic language. It’s spoken in Ethiopia, where the Lucy fossil was discovered. Dinkinesh is another Amharic word, meaning “marvelous.”

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