Asteroid Dactyl

The asteroid Dactyl is actually a moon of the asteroid Ida. Both are S type asteroids that show signs of space weathering, although Ida shows them more prominently. Dactyl’s official designation is (243) Ida I Dactyl. The asteroid Dactyl was discovered in images taken by the Galileo spacecraft during its flyby in 1993. These images provided the first direct confirmation of an asteroid moon. At the time, it was separated from Ida by a distance of 90 km and moving in a prograde. Dactyl’s surface is heavily cratered, like Ida’s, and consists of similar materials. Its origin is uncertain, but evidence from the flyby suggests that it originated as a fragment of the Koronis parent body.

The asteroid Dactyl is an egg shaped object measuring 1.6 by 1.4 by 1.2 km. It is oriented with its longest axis pointing towards Ida. Like Ida, Dactyl’s surface exhibits saturation cratering. It is marked by more than a dozen craters with a diameter greater than 80 m which indicates that the moon has suffered many collisions during its history. At least six craters form a linear chain, suggesting that it was caused by locally produced debris, possibly ejected from Ida. Dactyl’s craters may contain central peaks, unlike those found on Ida. These features, and Dactyl’s spherodial shape, imply that the moon is gravitationally controlled despite its small size. Like Ida, its average temperature is about -73°C.

The asteroid Dactyl shares many characteristics with Ida. Their albedos and reflection spectrum are very similar. The small differences indicate that the space weathering process is less active on Dactyl. Its small size would make the formation of significant amounts of regolith impossible. This is in direct contrast with Ida, which is covered by a deep layer of regolith.

It is thought that the asteroid Dactyl may have originated at the same time as Ida, perhaps from the disruption of the Koronis parent body. According to other theories it may have formed more recently, maybe as ejecta from a large impact on Ida. It is extremely unlikely that it was captured by Ida’s gravitational pull.

The asteroid Dactyl is of great interest to scientists since it was the first asteroid moon to be discovered. Its small size may have prevented regolith from forming, but that only allows better study of the asteroids true nature. Surely, this asteroid will be studied for years to come.

There is a great image of the asteroid Ida and its moon, the asteroid Dactyl, on NASA’s website. Here on Universe Today there are a couple of good articles about Ida and the asteroid Dactyl.

References:
NASA: Near Earth Object
Hyperphysics

Tagged as: asteroid dactyl, asteroid Ida, asteroid moon