[space] NASA's Lucy Spacecraft Reveals Asteroid Donaldjohanson as a Wobbling Peanut-Shaped Relic of Cosmic Violence

[StuckOnDestiny]

NASA's Lucy spacecraft made its closest approach to main-belt asteroid Donaldjohanson on April 20 and data from that encounter published this week reveals the asteroid as a wobbling, irregularly shaped contact binary, two objects fused together in a slow-spin wobble unlike anything previously observed up close. The asteroid, named after the anthropologist who discovered the famous human ancestor fossil that gives the Lucy mission its name, measures approximately 8 kilometres by 3.5 kilometres and wobbles on its axis in a way that tells scientists it was reshaped by forces after its initial formation rather than being simply the inert remnant of a two-body collision.

The encounter data from Lucy's cameras and instruments revealed surface features including a heavily cratered older terrain and smoother younger material, suggesting the asteroid has undergone significant geological evolution since its formation around 4.5 billion years ago in the early solar system. The unusual wobble, technically called a non-principal axis rotation, means Donaldjohanson is tumbling through space rather than spinning cleanly, an unusual condition that takes a specific kind of impact or gravitational interaction to produce and preserve.

Lucy is now continuing its journey toward Jupiter's Trojan asteroids, a swarm of primitive bodies that share the gas giant's orbit and are considered among the most pristine remnants of the early solar system. The spacecraft will make its first Trojan encounter with asteroid Eurybates in 2027 and will continue visiting Trojan targets through the 2030s. The Donaldjohanson encounter was Lucy's second main-belt asteroid flyby and the science return has already exceeded expectations.

Universe Today

[Wizard]

A wobbling peanut-shaped asteroid that has been tumbling through space for 4.5 billion years is the kind of object that makes you realise how strange and varied solar system bodies actually are compared to the smooth spheres we draw in textbooks

[Stu87]

Contact binaries, two objects that have slowly spiralled together and merged, are known to be common among small solar system bodies but we have rarely been able to image one with this kind of detail. Donaldjohanson is a rare close-up view

[AlexandrZakharyan]

The name Donaldjohanson linking the asteroid mission to the palaeontologist whose Lucy fossil discovery inspired the spacecraft name is the kind of intentional poetic connection NASA is very good at. The mission has a narrative coherence that makes it easy to follow

[Adam75]

Non-principal axis rotation being preserved over billions of years means the wobble-inducing event happened and nothing big enough to damp it has hit the asteroid since. It is a snapshot of a specific moment in solar system history

[PhotonBurst16]

Lucy's main act is the Trojan asteroids starting in 2027 and this is the warm-up. The Trojans have never been visited by a spacecraft and are thought to be some of the most primitive surviving material from the solar system's formation. The science from those encounters will be extraordinary

[DeepCourier]

The Lucy mission costing roughly a billion dollars and visiting twelve distinct solar system bodies over twelve years is one of the better value propositions in planetary science. Each encounter adds to a picture of how the solar system formed

[LuckyDrifter]

The smooth younger material visible alongside the heavily cratered older terrain on Donaldjohanson suggests the asteroid has been geologically active in a relative sense since formation. How small bodies renew their surfaces is an active research question