Ceres at Opposition

The biggest member of a belt of planetary flotsam is shining at its best right now. Ceres is the largest object in the asteroid belt — roughly a quarter the diameter of the Moon. And it’s lining up opposite the Sun, so it’s closest to us for the year, at more than 150 million miles. At that range it shines brightest, although not quite bright enough to see with the eye alone.

Ceres accounts for more than a quarter of the mass of the entire asteroid belt — a ring of rocky debris between Mars and Jupiter. The belt contains perhaps a million or more objects that are at least a kilometer in diameter, and countless other smaller ones.

Out of all of those chips of rock, ice, and metal, Ceres is the only one that’s built like a planet. Its gravity was strong enough to pull it into a spherical shape, for example. And it consists of several layers: a rocky core surrounded by an icy mantle, all wrapped in a crust of rock, ice, and salts.

A layer of liquid or frozen water may lie just below the crust. Some of that water appears to be escaping into space, giving Ceres a thin atmosphere. And an orbiting spacecraft found organic materials on the crust — the chemical building blocks for life. The combination means that conditions below the crust could be comfortable for life.

Ceres is passing through the constellation Cancer. Tonight, it’s high above the Moon in early evening. But you need binoculars to spot the little giant of the asteroid belt.

Script by Damond Benningfield