Until recently, there was a persistent belief that satellites can have only large space objects – planets or dwarf planets. The possibility of the existence of a satellite around the asteroid was considered only theoretically. In 1993, the Space Agency “Galileo”, heading for Jupiter, during the flight past the asteroid Ida discovered a 1.4 km satellite satellite. It was the first case of the satellite detection at the space object so small sizes – 60 × 25 × 19 km.
Idu opened in 1884 Austrian astronomer Johann Palis in the Vienna Observatory. The name object received in honor of the nymphs from ancient Greek mythology. The satellite found in one hundred nine years later the name Dactyl was assigned in honor of the mythical beings – drathiped on the island of Crete on Mount Ida.
The data obtained as a result of the “Galileo” span near the Ida asteroid, allowed to clarify some of the asteroid geology data. Ida is covered with craters of different ages, and on its surface is a thick layer of regolith. Old craters could have been formed at the time of the occurrence of Ida, during the breakdown of the parent asteroid, which formed the family of the Koronids. The largest crater LASC has 12 km in diameter.
The first spectrographic observations of Ida from the Earth made it possible to assert that this asteroid refers to the spectral class S. But the exact mineralogical composition of the asteroids of this class was unknown and approximately correlated with two classes of meteorites falling on the ground: chondrites of ordinary and pallasites. After the “Galileo” span, the average density of the Ida was determined – 3.2 g / cm³, which eliminates the presence of a large amount of substances with a high content of iron and nickel on its surface. The low density of the asteroid and the opening of the processes of cosmic weathering on its surface led to a certain revision of the relationship between asteroids of class S and chondrites of ordinary. It was previously believed that the main source of chondrites of ordinary were asteroids of class S. But, according to data obtained from the Galileo apparatus, their spectra often do not match.
Thus, there are good grounds to believe that only some asteroids of this class, including in the Koronide family, may be a source of chondrites of ordinary.