June 23, 2024

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The complex history of the small asteroid Dinkenish and its satellite Salam

The complex history of the small asteroid Dinkenish and its satellite Salam

On November 1, 2023, NASA’s Lucy probe flew over the asteroid (152830) Dinkenish and discovered an object with a complex structure and an attached fluorescence, named Slam. Several months later, we already know more details of the meeting that were published in nature This reveals a small world in the main asteroid belt that has a far from simple history. Lucy passed only 431 kilometers from Dinkenish at a relative speed of 4.5 kilometers per second, an asteroid with an average diameter of 719 meters and orbiting in 3.7 hours. Its Salam satellite orbits at a distance of 3.1 kilometers and actually consists of two equal-sized objects – 210 and 230 meters – connected by a small surface. Slam is subject to tidal coupling, so it always shows the same “face” to Dinkenish in its orbit, which has a period of 52.67 hours.

The “sunrise” of peace behind Dinkenish seen on 1 November 2023 at 16:55 UTC by the L’LORRI camera of the Lucy probe at 430 km (NASA/Goddard, SwRI, Johns Hopkins APL, NOIRLab/An-Li Tsai/NSYSU) .

Lucy’s images showed the presence of an equatorial mountain range similar to what we have seen in other nearby upper-type asteroids and debris such as Ryugu or Bennu. But what was not clear is that Dinkenish also has a canal covering its surface and crossing the Equatorial Mountain Range diagonally. According to the researchers who wrote the article, the channel was created when a mass equivalent to a quarter of an asteroid moved. This shift from Land Regolith releases matter into space. Part of it came together again to form the two parts of Salam and the rest fell back onto Dinkenish to form the Equatorial Mountain Range. The Dinkenish Tropical Range ranges from 150 to 230 meters wide and 40 to 100 meters high.

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Dinkenish model model (Harold F. Levison et al.).
Dinkinesh’s photos were taken with Lucy’s L’LORRI camera. In red you can see the Equatorial Mountain Range, and in yellow the channel from which the material that formed Silam is thought to have come (Harold F. Levison et al. / NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab).

In short, Dinkenish was a victim of the YORP Effect.Yarkovsky – O’Keefe – Radzewski – Paddack) It is a phenomenon that causes radical changes in the period of rotation of asteroids and the inclination of their axis due to differences in heat emission on their irregular surface. This effect is small, but constant, and after hundreds of thousands or millions of years, it sometimes causes asteroids to spin faster and faster. Depending on the asteroid’s internal structure, this accelerated rotation translates into sudden emissions of material that form new satellites and tropical mountain ranges. This tells us a lot about inside Dinkenish. If it had been a rubble pile-type asteroid like Bennu, the accelerated rotation period would have triggered regolith flows and a mountain range, but it would not have allowed for the creation of a satellite like Salam. Therefore, Dickenish’s internal cohesion must be greater, allowing him to release large pieces of rock.

Image from T2Cam shows the dual nature of Selam (NASA/Goddard/SwRI/Johns Hopkins APL).
Different Views of Peace (Harold F. Levison et al. / NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab).

The formation of a double-contact satellite is not at all straightforward and further studies and simulations will be necessary to understand how this phlongorium arises. There are three theories. First, that the matter expelled by Dinkenish directly generated two peace parts and that they were then united; Second, the satellites were formed in different episodes of physical expulsion; Third, the Proto-Selam pattern initially created by the YORP effect will be accelerated until it splits into two parts. What can be seen is that the inner body of Salam – which Dinkenish points to – also contains a small equatorial mountain range, which is evidence that it also went through the process of accretion of material present in its orbit. The Slam shape can be explained by the structure of a debris pile, although the internal cohesion must be greater than in the case of Dimorphos, the Didymos moon that NASA’s DART probe collided with. Taking into account that Dinkenish’s rotation period (3.7 hours) is longer than the 2.5 hours on average for nearby asteroids, it is expected that SLAM formed near Dinkenish and moved away over time by tidal interactions or by the Europ impact.

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Theories of peace formation (Harold F. Levison et al.).

The encounter with Dinkenish shows us, once again, that asteroids can represent enormous morphological and evolutionary complexity. Despite all the ones we have studied closely, we need to visit more of them. Of course, many surprises await us.

References:

  • https://www.nature.com/articles/s41586-024-07378-0
  • https://www.nasa.gov/solar-system/asteroids/nasa-lucy-images-reveal-asteroid-dinkinesh-to-be-surprisingly-complex/