Comet
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A comet is an icy, small Solar System body or interstellar object that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitat
Comet Hale–Bopp after passing perihelion in April 1997
Structure of a comet
Comet 81P/Wild exhibits jets on light side and dark side, stark relief, and is dry.
Hubble image of Comet ISON shortly before perihelion.
Asteroid
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An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the inner Solar System or is co-orbital with Jupiter. Asteroids are
Comet
…the orbit of Jupiter rather than in the outer Solar System. However, the discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were…
A composite image, to the same scale, of the asteroids imaged at high resolution prior to 2012. They are, from largest to smallest: 4 Vesta, 21 Lutetia, 253 Mathilde, 243 Ida and its moon Dactyl, 433 Eros, 951 Gaspra, 2867 Šteins, 25143 Itokawa.
Vesta (left), with Ceres (center) and the Moon (right) shown to scale
Giuseppe Velasquez, Giuseppe Piazzi and Ceres, oil on canvas, c. 1803
2013 ET, shown here in radar images, has a provisional designation