Dinkinesh is a small asteroid orbiting the Sun near the inner edge of the main asteroid belt. NASA’s Lucy spacecraft recently revealed that this asteroid, with an effective diameter of just 720 meters, is unexpectedly complex. The asteroid has a pronounced valley covered by an equatorial ridge and is currently orbited by a contact binary moon, named Seram, which consists of two nearly equal lobes with diameters of 210 meters and 230 meters. The moon orbits at a distance of 3.1 kilometers from Dinkinesh, has an orbital period of about 52.7 hours, and is tidally locked.
Stereo image pair (a-c) taken by the L’LORRI instrument aboard NASA’s Lucy spacecraft on November 1, 2023, shows asteroid Dinkinesh. Yellow and rose dots indicate valley and ridge features, respectively. These images have been sharpened and processed to enhance contrast. Image (d) shows a side-on view of Dinkinesh and its moon Ceram, taken a few minutes after closest approach. Image credit: NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab.
“We want to understand the strength of small bodies in the solar system because it’s important to understanding how planets like Earth got here,” said Dr. Hal Levison, a research scientist at Southwest Research Institute and Lucy principal investigator.
“Essentially, planets formed when a bunch of tiny objects orbiting the sun, like asteroids, collided with each other.”
“How objects behave when they collide – whether they break or stick together – has a lot to do with the object’s strength and internal structure.”
The researchers believe that how Dinkinesh responded to stress may reveal something about its inner workings.
As it rotated in sunlight for millions of years, tiny forces from thermal radiation radiating from the asteroid’s warm surface created tiny torques that caused Dinkinesh to spin gradually faster, and the accumulated centrifugal forces caused parts of the asteroid to become more elongated.
This event likely sent debris into close orbit, providing the raw material for the formation of the ridge and moons.
If Dinkinesh had been a weaker, more mobile mass of sand, its particles would have gradually migrated toward the equator and then blasted off into orbit as it rotated faster.
But the images suggest that, like rock, the Dinkinesh asteroid was stronger than a fluid and held together longer, until it eventually disintegrated under pressure and broke into larger pieces. Still, the force needed to break up a small asteroid like Dinkinesh is tiny compared to most rocks on Earth.
“This valley suggests a sudden collapse, more like an earthquake, where stress builds up gradually and then is suddenly released, rather than the slow process that creates sand dunes,” said Dr. Keith Noll, a research scientist at NASA’s Goddard Space Flight Center and a Lucy scientist.
“These features show that Dinkinesh has some strength, and we can do a bit of historical reconstruction to see how this asteroid evolved,” Dr Levison said.
“During that collapse, the rocks broke apart and things separated, forming a disk of material, some of which rained down to the surface and formed the ridge.”
“We think that some of the material in the disk formed the moon Ceram, which is actually a structure where two celestial bodies are in contact with each other, known as a contact binary. The details of how this unusual moon formed remain a mystery.”
of Investigation result Published in the journal Nature.
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H.F. Levison others2024. Contact binary moon of asteroid (152830) Dinkinesh. Nature 629, 1015-1020; doi: 10.1038/s41586-024-07378-0
