NASA can’t believe it: this asteroid not only has its own moon, but it is also “conjoined”

In a rather unexpected discovery, the NASA spacecraft Lucy has revealed that the asteroid Dinkinesh, colloquially known as “Dinky”, has a peculiar companion: a binary contact satellite, that is, two fused moons, which researchers have named “Selam”. The finding, published in the journal Nature on May 29, 2024, challenges existing theories about the formation of asteroids and celestial bodies.

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Jessica Sunshine, professor of Astronomy and Geology at the University of Maryland and co-author of the article, highlighted the unexpected complexity of these small celestial bodies. “With the additional observations made by the spacecraft, we were able to better analyze features such as Dinkinesh’s rotation speed and Selam’s orbital pattern,” she explained.

The images sent by Lucy showed a significant depression in Dinkinesh, suggesting that approximately a quarter of the asteroid detached from its main body. This detachment, possibly caused by Dinky’s rapid rotational movement, resulted in the expulsion of rocky debris into orbit. Some of this debris clustered together to form Selam, while others fell onto Dinky, creating visible ridges in the photographs.

Hal Levison, principal scientist of the Lucy mission, emphasized the importance of understanding the resistance and internal structure of asteroids in order to understand how planets formed. “Planets formed when smaller objects like asteroids collided with each other. Whether objects break apart or stay together when they collide has a lot to do with their strength and internal structure,” he said.

Although how Selam formed remains a mystery, Sunshine pointed out that the findings open the door to comparative studies with similar celestial bodies, such as the binary system Didymos. This system shares many similarities with Dinky, despite being located in different parts of the solar system.

Dinkinesh and Selam are the first of the 11 asteroids that Lucy will explore in its 12-year mission. After its next visit to Earth in December 2024 for a gravity assist, the spacecraft will observe the Donald Johanson asteroid in April 2025 and the Trojan asteroids in 2027. Sunshine concluded that studying these asteroids is essential to understand how planets form and, ultimately, the Earth itself.

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