Ceres,Vesta, and Pallas: Protoplanets, Not Asteroids
Abstract
Objects in our solar system are currently thought to have formed by condensation and accumulation from the gas and dust nebula, out of which the Sun first arose. Dust grains accreted to form objects of approximately one-kilometer in size, which in turn accreted to form objects of about 1000 kilometers in size. Some of these objects grew to become the planets, and formed a core, mantle, and crust layers through radioactive heating, which melted some or all of the material, and subsequent differentiation.The development of large planets caused gravity perturbations, rearranging the remaining debris and halting the accretion. Inside five astronomical units (AU, where one AU is the mean distance of the Earth from the Sun), only the terrestrial planets remain, except for the Asteroid Belt, which is shepherded by Jupiter's gravity. The asteroid belt mostly contains many small objects that show signs of heating and melting and are probably left over from the mutual destruction of intermediate-sized objects in the accretion chain. These fragments are what are generally thought of when one speaks of asteroids. However, a few of the intermediate, approximately 1000-kilometer-sized objects in the asteroid belt seem to be intact: Vesta, Ceres, and Pallas. This article points out that, although these objects also have been classified as asteroids, they instead appear to be small planets, or protoplanets. Their existence today helps confirm this general theory of planet formation, and provides evidence for the study of the terrestrial planet formation process.
- Publication:
-
EOS Transactions
- Pub Date:
- March 2006
- DOI:
- 10.1029/2006EO100002
- Bibcode:
- 2006EOSTr..87..105M
- Keywords:
-
- Planetary Sciences: Solid Surface Planets: Composition (1060;
- 3672);
- Planetary Sciences: Comets and Small Bodies: Interiors (8147);
- Planetary Sciences: Solar System Objects: Asteroids