In November 2023, NASA’s Lucy probe flew by the asteroid Dinkinesh, arriving within 431 km of its surface and discovering the presence of a binary companion. Companion who in reality turned out to be double himself, precisely a contact trackcomposed of two small rocky objects that touch each other.
Recently the images obtained by Lucy during the flyby have allowed us to analyze in more detail the history of this asteroid system, whose structure is particularly complicated. Dinkinesh shows a ridge and trough, where a large chunk, about a quarter of the asteroid, may have suddenly moved. And then there’s the contact binary, now known as Selam, which was once part of the main asteroid body.
This structure demonstrates that Dinkinesh and Selam have significant internal strength, and a complex and dynamic story that scientists are now beginning to define.
The story of Dinkinesh
Lucy’s observations highlight interesting information about Dinkinesh, which is only 720 meters in diameter. It shows a ridge in the equatorial direction and a trough, a depression in the longitudinal direction, where a large piece, about a quarter of the asteroid, may have suddenly moved. The contact track, now known as Selam, consists of two lobes of almost equal size, with diameters of 210 and 230 meters. It orbits 3.1 km from Dinkinesh with an orbital period of approximately 52.7 hours.
Dinkinesh, like other asteroidal and planetary bodies in our Solar System, reveals its internal structure based on how it has responded to stress over the course of its evolution.
The dynamical state, angular momentum, and geomorphological observations of the system allowed the researchers to deduce that the Dinkinesh ridge and trough are likely the result of mass failure. “A sudden failure, more like an earthquake with a gradual build-up of stress and then a quick release, rather than a slow process like the formation of a sand dune,” explained Keith Noll, NASA GSFC scientist and co-author of a paper that reports these results.
The Selam contact binary, scientists say, likely built up from material lost from this event. Event caused by the fact that, during the millions of years in orbit around the Sun, the forces coming from the thermal radiation emitted by the hot surface of the asteroid caused part of its material to give way and lose. Consequently Dinkinesh it started to rotate faster and fasteraccumulating centrifugal tensions until part of the asteroid has shifted, into a more elongated shape and forming the ridge.
Mission Lucy continues
Dinkinesh and its satellite are the first two of 11 asteroids that Lucy’s team plans to explore over the course of its 12-year journey. After having skimmed the inner edge of the Main Belt, between Mars and Jupiter, Lucy is now returning towards Earth.
In December 2024 he will perform a maneuver gravity assist with our planet, to be pushed again in the direction of the Main Belt. Here in 2025 the asteroid Donaldjohanson will be observed. Then, starting in 2027, Lucy will have the first of its encounters with the Trojan asteroids that guide and follow Jupiter in its orbit around the Sun.
More information on the mission here.
The study that reports the results discussed in the article, however, can be found here.
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