Kids: Asteroids part of an ancient planet?
Asteroids Ida and Dactyl, image credit: Galileo Project, JPL, NASA. For a full caption, click here.
Are the asteroids part of an ancient planet?
An Earth & Sky listener wrote, “There’s an asteroid belt outside the orbit of Mars. If all these asteroids were combined in mass, how big would the resulting planet body be? And are the asteroids part of some ancient planet?
Astronomers once speculated that asteroids might be the result of an ancient explosion in our solar system – in which an entire planet broke apart.
But today’s astronomers don’t think that. They see the asteroids as the parts of a planet that never formed. It’s thought that our solar system formed from a huge cloud of gas and dust in space. As time passed, particles in the cloud clumped together to form tiny proto-planets called planetesimals. These later came together to form the planets we know today.
There was room for another planet between Mars and Jupiter. A planet didn’t form there – Jupiter’s powerful gravity probably wouldn’t let another planet form so nearby. Today, there are some 100,000 known asteroids. Astronomers believe that our solar system might contain about a million asteroids with diameters greater than one kilometer – or about two-third of a mile.
Still, it’s thought that if you could clump all these asteroids together, you’d have an object with less than 10% the mass of Earth’s moon.
More info:
Italian astronomer Giuseppe Piazzi spotted the first asteroid in 1801 during a search for a hidden planet that was believed to exist near Mars. The asteroid was 1000 kilometers across and named Ceres.
Asteroids are also found in places such as the orbit of Jupiter (Trojan asteroids) and crossing the Earth’s orbit (Apollo asteroids).
The material that makes up asteroids may be unchanged from when they formed 4.5 billion years ago. By examining the chemical and mineral make-up of these objects, it may provide scientists with a better picture of the early solar system.
Ask An Astronomer: Are the asteroids the remains of a planet?
Astronomy Cafe: Was there ever a planet between the orbits of Mars and Jupiter?
