Are the asteroids the remains of a planet which broke apart? (Beginner)

I have recently been introduced to the thought that the asteroid belt between Mars and Jupiter contains the remains of a planet named Astera which had fragmented before it was able to solidify. Could you please forward any information you may have on this subject. Thank you for your time....

Off and on, people suggest that the asteroid belt is the remains of a planet (sometimes called Phaeton) which either disintegrated or never quite got put together right.

The total mass in the asteroid belt is only about 4% of the mass of Earth's Moon. About half of that total is in the four most massive asteroids (Ceres, Vesta, Pallas, and Hygiea). Even if all the asteroids were to get together to form a single object, that "planet" might be considered just a dwarf planet.

Moreover, the asteroids' diverse chemical compositions indicate that they were not all once part of a single body, but formed as a very large number of smaller bodies, some of which did later break apart to form even smaller bodies.

So, the answer I think is "no." Even if all the asteroids had come from a single parent body (the evidence is that they didn't), that parent body would be too small to be called a planet.

Here's an answer to a similar question from NASA's "Ask an Astrophysicist" site: (see "Could the Asteroid Belt be a destroyed planet?")

This page was last updated by Sean Marshall on July 18, 2015.

About the Author

Dave Kornreich

Dave was the founder of Ask an Astronomer. He got his PhD from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question.