You are here

Asteroid Hunting

July 13, 2014

The planet Mars and the star Spica team up for a beautiful showing in the southwest this evening. As night falls, bright orange Mars is just a degree or two above Spica — less than the width of a finger held at arm’s length.

If you draw a line from Spica to Mars and continue it upward by less than the width of your fist, you’ll come to two members of our own solar system that are staging an even closer encounter — Ceres and Vesta. They’re not quite bright enough to see with the eye alone, though — you need a telescope to spot them.

Ceres is the largest object in the asteroid belt — a wide band of rubble between the orbits of Mars and Jupiter. It’s a ball of rock and ice about one-quarter the diameter of the Moon. Despite its diminutive size, a few years ago Ceres was classified as a dwarf planet — one of five objects to receive that designation so far.

Vesta is the second most-massive asteroid after Ceres. It’s about half the size of Ceres, but it’s also closer to Earth, and its surface is more reflective, so it’s the brightest asteroid. Although it’s not a dwarf planet, it’s built a bit like a planet, with a dense core surrounded by a mantle and crust of lighter rock.

We learned a lot more about Vesta from the Dawn spacecraft, which orbited the big asteroid for more than a year. Dawn left orbit in late 2012, and is en route to Ceres. It’ll arrive next February — providing our first close look at any dwarf planet.


Script by Damond Benningfield, Copyright 2014

Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.