10 Need-to-Know Things About Asteroids:
- If all of the asteroids were combined into a ball, they would still be much smaller than Earth's moon. If the sun was as tall as a typical front door, Earth would be the size of a nickel, the moon would be about as big as a green pea and Ceres (the largest object in the main asteroid belt) would be as small as a sesame seed.
Dawn: First to orbit an asteroid - Most Asteroids orbit our sun, a star, in a region of space between the orbits of Mars and Jupiter known as the Asteroid Belt.
- Days and years vary by asteroid. A day on asteroid Ida, for example, takes only 4.6 hours (the time it takes to rotate or spin once). Ida makes a complete orbit around the sun (a year in this asteroid's time) in 4.8 Earth years.
- Asteroids are solid, rocky and irregular bodies.
- Asteroids do not have atmospheres.
- More than 150 asteroids are known to have a small companion moon (some have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.
- Asteroids do not have rings.
- More than 10 spacecraft have explored asteroids. NEAR Shoemaker even landed on an asteroid (Eros). The Dawn mission is the first mission to orbit (2011) a main belt asteroid (Vesta).
- Asteroids cannot support life as we know it.
- Ceres, the first and largest asteroid to be discovered (1801 by Giuseppe Piazzi) and the closest dwarf planet to the sun, encompasses over one-third of the estimated total mass of all the asteroids in the asteroid belt.
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