Asteroids are rocky or metallic airless objects that orbit our sun, and are too small to be called planets.
Millions of these are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter.
Despite how they appear in drawings, each asteroid is generally many miles away from the next asteroid. (Not like the asteroid belt as seen in Star Wars movies!)
Asteroids that pass close to Earth are called near-earth objects.
10 Need-to-Know Things About Asteroids
1. If all of the asteroids were combined into a ball, they would still be much smaller than Earth’s moon. If the sun were 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.
2. Most Asteroids orbit our sun, a star, in a region of space between the orbits of Mars and Jupiter known as the Asteroid Belt.
3. 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.
4. Asteroids are solid, rocky and irregular bodies.
5. Asteroids do not have atmospheres.
6. 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.
7. One asteroid, named Chariklo, is known to have two dense and narrow rings.
8. 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).
9. Asteroids cannot support life as we know it.
10. 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.
Sizes and shapes
Here are the comparative sizes of eight asteroids
Lutetia has a diameter of 81 miles (130 km)
Vesta has diameter of 330 miles (530 km)
Image credit: NASA/JPL-Caltech/JAXA/ESA
Where are the asteroids found?
1. Main asteroid belt
2. At the Lagrangian points around Mars, Jupiter – the Trojans and Greeks, and around Neptune
3. Many are also found much further out in the Kuiper belt.
(However most objects in the Kuiper belt are believed to be more comet-like.)
NASA’s Asteroid Redirect Mission
NASA is developing a first-ever robotic mission to visit a large near-Earth asteroid, collect a multi-ton boulder from its surface, and redirect it into a stable orbit around the moon. Once it’s there, astronauts will explore it and return with samples in the 2020s. This Asteroid Redirect Mission (ARM) is part of NASA’s plan to advance the new technologies and spaceflight experience needed for a human mission to the Martian system in the 2030s.
Difference between comet and asteroids
Comets are mostly ice. Most comets develop a thin atmosphere when they are closer to the Sun; parts of their atmosphere may get visibly blown away from the Sun, as a “tail.”
“Extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust – and may thus come to resemble small asteroids.”
Asteroids are mostly rock, metal, and/or carbon compounds. Most asteroids do not have an asteroid or tail. “The discovery of main-belt comets and active centaurs has blurred the distinction between asteroids and comets.”
Next Generation Science Standards
MS-ESS1 Earth’s Place in the Universe
ESS1.B: Earth and the Solar System – The solar system consists of the sun and a collection of objects, including planets, their moons, and asteroids that are held in orbit around the sun by its gravitational pull on them. (MS-ESS1-2),(MS-ESS1-3)