24 Themis is one of the largest asteroids in the asteroid belt, and researchers recently discovered that it's entirely coated in a thin layer of ice. It may be a remnant of the frozen space rocks that created Earth's oceans.
Last week, two articles in Nature described the discovery of water ice on 24 Themis. Using an infrared telescope, an international team of researchers analyzed the spectrum of light reflected off the asteroid's surface. The pattern of light absorption and reflection was characteristic of frost combined with various minerals on the asteroid's surface.
Scientists have speculated that asteroids in the belt between Mars and Jupiter might contain water ice, which would be a boon to space colonists who need to stock up on water on their way to the outer planets. It's also likely that this frosty asteroid will provide a key to how the Earth's oceans formed on what started as a dry dirtball. Asteroids like 24 Themis crashed to Earth, bringing water with them.
Describing the discovery in Nature, astrophysics researcher Henry Hsieh writes:
24 Themis is part of a "family" of asteroids that were originally part of the same body but were shattered by an impact about a billion years ago. Above you can see an artist's conception of the asteroid along with two small fragments of its family. You can see that one of the fragments has a comet-like tail, which scientists speculate is caused when water evaporates from its surface.
Image by Gabriel Pérez, Servicio MultiMedia, Instituto de Astrofisica de Canarias, Tenerife, Spain.