Eros (astronomy)

Eros (astronomy), asteroid discovered through photography at the Urania Observatory in Berlin, Germany, in 1898. It is of interest to astronomers because it comes closer to Earth than any other body of comparable size, with the exception of the Moon. At times it approaches within 24.2 million km (15 million mi) of Earth.

Because Eros comes so close to Earth, the gravitational field of Earth causes deviations in the asteroid’s orbit, and extremely precise micrometric measures can be made of its position in the heavens. These measurements make calculation of the distances between Eros, Earth, and the Sun possible. These distances are important because accurate determinations of the absolute dimensions of the solar system and of interstellar distances cannot be made without them. During a particularly close approach by Eros to Earth in 1931, an international effort was made to determine these distances. Observations were made at 36 places on six continents. English astronomer Sir Harold Jones performed the calculation of the mean distance from Earth to the Sun, and in 1941 he announced the new value of 149.6 million km (92.9 million mi).

Eros is potato-shaped and measures about 33 km (about 21 mi) in its longest dimension. It has been found to vary periodically in brightness. Careful photometric study has revealed that the planetoid is much brighter on one side than on the other and that the periodicity of brightness is caused by its rotation on its axis.

In February 1996 the National Aeronautics and Space Administration (NASA) launched the Near-Earth Asteroid Rendezvous (NEAR) spacecraft (later renamed NEAR Shoemaker) to map the surface of Eros and gather data to determine the asteroid’s composition and structure. In February 2000 the spacecraft reached Eros, moved into orbit around the asteroid, and began making observations. NASA decided to attempt a landing after the spacecraft had completed all of its mission objectives. Although NEAR Shoemaker was not designed to land, it touched down intact on the surface of Eros in February 2001. NEAR Shoemaker was the first spacecraft ever to land on an asteroid.