Selam, formal designation Dinkinesh I, is a

contact binary In astronomy, a contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes. A binary system whose stars share an envelope may also be called an overcontac ...

and

natural satellite A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites are colloquially referred to as moons, a deriv ...

of the main belt asteroid 152830 Dinkinesh. It was discovered on November 1st, 2023 during Lucy's flyby of Dinkinesh. Lucy took pictures of the asteroid, and sent data back to

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

leading to the discovery of the moon.

Naming

Selam was named after the fossilized remains of an

Australopithecus ''Australopithecus'' (, ; or (, ) is a genus of early hominins that existed in Africa during the Pliocene and Early Pleistocene. The genera ''Homo'' (which includes modern humans), ''Paranthropus'', and ''Kenyanthropus'' evolved from some ''Aus ...

, named Selam (ሰላም) also known as "Lucy's daughter" although being some 100,000 years older than the fossilized remains of another Australopithecus known as

Lucy Lucy is an English language, English feminine given name derived from the Latin masculine given name Lucius with the meaning ''as of light'' (''born at dawn or daylight'', maybe also ''shiny'', or ''of light complexion''). Alternative spellings ar ...

, but Dink'inesh in

Amharic Amharic is an Ethio-Semitic language, which is a subgrouping within the Semitic branch of the Afroasiatic languages. It is spoken as a first language by the Amhara people, and also serves as a lingua franca for all other metropolitan populati ...

. Selam (which also means "peace" in the

language) was chosen for the moon, as the name of the asteroid it orbits around is " Dink'inesh". The name Selam was proposed by astronomer Raphael Marschall. The spaceship ''Lucy'' which discovered Selam was also named after the Australopithecus Lucy.

Theorized origin

Selam is theorized to have been formed out of the same material and same surface texture as other rubble pile asteroids found in the asteroid belt. These rubble pile asteroids were thought to be created out of a mass shedding event that happened to the asteroids themselves. Selam is believed to be very young at about 2 to 3 million years old when it first separated from Dinkinesh

Lucy mission

On 1 November 2023, Lucy successfully flew by its first target, the

main-belt asteroid The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

152830 Dinkinesh, at a relative speed of . On the following day, NASA released images from the flyby and announced the discovery of a small satellite orbiting Dinkinesh. The first images from the flyby showed that Dinkinesh is approximately in diameter, while the satellite is approximately in diameter. Later images showed that the satellite was actually two objects in direct contact, known as a contact binary. The discovery of Dinkinesh's satellite brought the total number of Lucy's planned

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

visits up to eleven.

Discovery

In January 2017, Lucy and the Psyche missions were chosen as Discovery Mission 13 and 14 respectively. Lucy's first target for its mission was the asteroid, Dinkinesh, which was discovered in 1999. On 1 November 2023 Lucy flew by the Dinkinesh system, taking pictures and sending data back to NASA. A day after the flyby, NASA released pictures of the Dinkinesh system, with the discovery of Selam.

References

{{Use dmy dates, date=May 2025 Contact binary (small Solar System body) Astronomical objects discovered in 2023 Asteroid satellites