Discovery and exploration of the Solar System Earth to be orbited by an artificial satellite ("Luna 10"), followed by Mars in 1971 ("Mariner 9"), Venus in 1975 ("Venera 9"), Jupiter in 1995 ("Galileo"), the asteroid 433 Eros in 2000 ("NEAR Shoemaker"), Saturn in 2004 ("Cassini–Huygens"), and Mercury and Vesta in 2011 ("MESSENGER" and "Dawn" respectively). "Dawn" is orbiting the asteroid–dwarf planet Ceres as of 2015. The first probe to land on another Solar System body was the Soviet "Luna 2" probe, which impacted the Moon in 1959. Since then, increasingly distant planets have been reached, with probes landing on or impacting the surfaces of Venus in 1966
Minor planet asteroids. A minor planet seen releasing gas may be dually classified as a comet. Objects are called dwarf planets if their self-gravity is sufficient to achieve hydrostatic equilibrium and form an ellipsoidal shape. All other minor planets and comets are called "small Solar System bodies". The IAU stated that the term "minor planet" may still be used, but the term "small Solar System body" will be preferred. However, for purposes of numbering and naming, the traditional distinction between minor planet and comet is still used. Hundreds of thousands of minor planets have been discovered within the Solar System and thousands