What is the difference between an asteroid and a comet?
Asteroids are rocky or metallic bodies that mostly orbit between Mars and Jupiter. Comets contain much more ice and grow glowing comas and tails when they near the Sun.
Asteroids are leftover building blocks from the formation of the solar system about 4.6 billion years ago. Most lie in the main asteroid belt between Mars and Jupiter. They range from tiny rocks to Ceres, about 940 kilometers wide, which is now classed as a dwarf planet. Asteroids usually look like points of light, even through telescopes.
Comets formed farther from the Sun, where it was cold enough for water, carbon dioxide and other gases to freeze. Most spend their time in the Kuiper Belt or the distant Oort Cloud. When their long orbits bring them close to the Sun, the ice vaporizes, creating the fuzzy coma and tails that make comets so recognizable.
Blurry lines
Scientists have found objects that fall between the two groups. Some asteroids in the main belt release dust like comets, and some old comets have lost their ice and now look like asteroids. NASA's DART mission crashed into the small asteroid Dimorphos in 2022, successfully changing its orbit as a test of planetary defense.
Did You Know?
Asteroids are usually named by their discoverers, while comets are traditionally named after the people or projects that found them.