Double moon of asteroid Dinkenish | EOS Sciences

Opening image: An image of Salaam, the small moon orbiting the asteroid Dinkenish. Later photos showed that Salam consisted of two pieces. © NASA/JHU-APL

Lucy, named after the famous Ethiopian fossil Australopithecus afarensis Which sheds new light on human evolution, was launched in October 2021. The space probe will visit seven so-called Trojans, which are asteroids orbiting the Sun in the same orbit as the giant planet Jupiter. Lucy's research should provide more information about the evolution of the solar system.

However, on November 1, 2023, the space probe also flew close to a small section in the vast asteroid belt between the orbits of Mars and Jupiter. This celestial body, which was discovered in 1999 using a telescope in New Mexico, was named Dinkenish. This is the Ethiopian name for the Lucy fossil and means “You are beautiful.” It is the smallest asteroid belt object ever closely studied.

Images taken during Dinkenish's pass (at a speed of 4.5 kilometers per second at a distance of only 430 kilometers) show that the large 790-meter asteroid is accompanied by a large 220-meter-long moon, which is now called Salam. Salam (Ethiopian word meaning “peace”) is another name Australopithecus afarensis-Fossil.

Salam at first looked like a single rock. But images taken some time after the closest approach show that the Moon itself consists of two small celestial bodies. The two rocks are almost touching each other – this is called Bilateral communication. Such “double” objects have been discovered before in the solar system, but this is the first time that one has been discovered. Bilateral communication It was found orbiting an asteroid.

The double moon likely formed from material ejected from Dinkenish's surface due to its high rotation speed.
In April 2025, Lucy will also fly by asteroid Donald Johansson (named after the human paleontologist who discovered Lucy's fossil in 1974). The space probe will not reach the 70-kilometre-long Eurybates asteroid, the first Trojan on the itinerary, until August 2027.