Lucy Sees its Next Target: Asteroid Donaldjohanson

NASA’s asteroid-studying spacecraft Lucy captured an image of its next flyby target, the asteroid Donaldjohanson. On April 20th, the spacecraft will pass within 960 km of the small, main belt asteroid. It will keep imaging it for the next two months as part of its optical navigation program.

Donaldjohanson is an unwieldy name for an asteroid, but it’s fitting. Donald Johanson is an American paleoanthropologist who discovered an important australopithecine skeleton in Ethiopia’s Afar Triangle in 1974. The female hominin skeleton showed that bipedal walking developed before larger brain sizes, an important discovery in human evolution. She was named Lucy.

NASA named their asteroid-studying mission Lucy because it also seeks to uncover clues about our origins. Instead of ancient skeletal remains, Lucy will study asteroids, which are like fossils of planet formation.

During its 12-year mission, Lucy will visit eight asteroids. Two are in the main belt, and six are Jupiter trojans. Asteroid Donaldjohanson is a main-belt, carbonaceous C-type asteroid—the most common variety—about 4 km in diameter and is Lucy’s first target. It’s not one of the mission’s primary scientific targets. Instead, the flyby will give Lucy mission personnel an opportunity to test and calibrate the spacecraft’s navigation system and instruments.

The animation below blinks between images captured by Lucy on Feb. 20th and 22nd. It shows the perceived motion of Donaldjohanson relative to the background stars as the spacecraft rapidly approaches the asteroid.

via GIPHY

The flyby is like a practice run before Lucy visits the Jupiter trojans. These asteroids are clusters of rock and ice that never coalesced into planets when the Solar System formed. These are the “fossils of planet formation,” the most well-preserved evidence from the days of Solar System formation.

Currently, Donaldjohanson is 70 million km away and will remain a tiny point of light for weeks. Only on the day of the encounter will the spacecraft’s cameras capture any detail on the asteroid’s surface. In the images above, the dim asteroid still stands out from the dimmer stars of the constellation Sextans. Lucy’s high-resolution L’LORRI instrument, the Long Lucy LOng Range Reconnaissance Imager, captured the images.

Lucy is following a unique flight pattern. It’s essentially a long figure-eight.

Even this early in its mission, Lucy has delivered some surprising results. In November 2023, it flew past asteroid 152830 Dinkinesh. The flyby was intended as a test for the spacecraft’s braking system, but instead, it revealed that Dinkinesh has a small satellite. Closer observations showed that the satellite is actually a contact binary, which means it’s composed of two connected bodies. This was a valuable insight into asteroids.

There are surprising discoveries in every mission, and Lucy is no exception. As it makes its way through its list of targets, it will almost certainly show us some surprises.

The Trojans are difficult to study from a distance. They’re a long way away. Scientists aren’t certain how many there are; there may be as many Trojans as there are main-belt asteroids. The Trojans exhibit a wide variety of compositions and characteristics, which could indicate that they came from different parts of the Solar System. By studying the Trojans in all their diversity, Lucy will hopefully help scientists reconstruct their origins and how they were captured by Jupiter.

The Solar System has a long history and we’ve only just become a part of it. Some of the clues to our origins are out there among the battered rocks of the asteroid belt and the Jupiter Trojans. Lucy will give us our best look at the Trojans. Who knows what it might reveal?

• Press Release: NASA’s Lucy Spacecraft Takes Its 1st Images of Asteroid Donaldjohanson
• Press Release: NASA Lucy Images Reveal Asteroid Dinkinesh to be Surprisingly Complex
• ASU Institute of Human Origins: Lucy’s Story

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