Subduction Zone
Veteran Member
I had to Google it since it is a fact that I cannot remember, but this raised the question of how large an object has to be to become spherical. In other words, how large does an object need to be so that its own gravity is strong enough to force it to be a sphere. And it is a bit large than asteroids. For a rocky object it needs to be at least 600 km in diameter and for an icy object only 400 km (ice is not as strong as rock):Always glad to oblige.
Probably because its gravity is too weak and because it is in the stronger gravitational field of the Earth.
The Earth is not bilobar because its gravitational field is strong enough to force it into a spherical shape. The Moon was probably ejected from the proto-Earth by a collision with a Mars-sized planet about 4.5 billion years ago; since then tidal interactions between the Earth and the Moon have slowed the Earth's rotation and driven the Moon outwards to its present distance. The Earth is ellipsoidal because of its rapid rotation. I doubt whether the Moon is ellipsoidal; its departures from sphericity may be due to impact excavation of the mare basins and deposition of ejecta from these basins to form the highlands.
Space.com: NASA, Space Exploration and Astronomy News
Get the latest space exploration, innovation and astronomy news. Space.com celebrates humanity's ongoing expansion across the final frontier.
www.spaceanswers.com
EDIT: But what about Ceres? Ceres is no longer an asteroid. It is a dwarf planet. When Pluto was "demoted" the change in classification changed Ceres from an asteroid to a dwarf planet. If an object is large enough to have to be spherical it is by definition no longer an asteroid. And for comparison the top four "asteroids":
Ceres (dwarf planet) - Wikipedia
en.wikipedia.org
Last edited: