Asteroid Ida | Universe Today

Written by Jerry Coffey

The asteroid Ida, number 243, is a member of the Koronis family in the main belt. It was discovered on September 29, 1884 by Johann Palisa. The asteroid Ida is an S-type asteroid with its own satellite or moon. On August 28, 1993, Ida was visited by the spacecraft Galileo. It was the second asteroid to be visited and the first to have its own moon. The moon has been named Dactyl.

The asteroid Ida has an average diameter of 31.4 km and a mass of 4.2×10¹⁶ kg. The close flybys that Galileo had of Ida, Gaspara, and the NEAR Shoemaker allowed the firs observations of asteroid geology. Ida is classified as an S-type based on ground based measurements. Before Galileo, the composition of S-types was uncertain. They were thought to contain stoney iron and chondrite, but because of Ida's density, stoney iron was ruled out.

The Galileo images also led to the discovery that space weathering was taking place on the asteroid Ida, a process which causes older regions to become more red in color over time. The same process affects both Ida and its moon, although Dactyl shows a lesser change. The weathering of Ida's surface revealed another detail about its composition: the reflection spectra of freshly exposed parts of the surface resembled that of OC meteorites, but the older regions matched the spectra of S-type asteroids. S-types are the most common asteroids found in the Solar System and OC meteorites are the most common found on Earth. The weathering on Ida suggests that S-type asteroids are the source of OC meteorites.

The asteroid Ida is covered in a thick blanket of regolith. Regolith is pulverized rock that occur during an impact event. This layer is between 50-100 m thick and covers the entire asteroid. The regolith on Ida consists of the silicate minerals olivine and pyroxene.

Although the asteroid Ida was visited nearly seventeen years ago, it is still influencing modern asteroid exploration. Several theories were dismissed and actual evidence took their place. That is the beauty of astronomy.

On Universe Today we have written about Ida's close approach several times to give you plenty of information. We also have links to images and other opinions about Ida as well as a great Astronomy Cast feature about asteroids.

Filed under: Astronomy