Letting off steam – scientists discover water on an asteroid

Infrared images from the Herschel Space Telescope have identified water on the surface of an asteroid for the first time. Observations of the dwarf planet Ceres, the largest asteroid within the asteroid belt, have confirmed the presence of water vapour. The telescope measures the amount of heat radiated from the asteroid surface, with a decrease in radiation hinting at the presence of water.

However, observations made over the course of the year failed to consistently detect water. Allied with an apparently fluctuating water volume at the asteroid surface, this detail led the researchers to postulate that the water was ejected episodically as steam from different locations on the asteroid.  This phenomenon is thought to occur when the orbit of Ceres brings it to its closest point to the sun, allowing the surface to heat up enough to melt the icy surface just a little.

These unprecedented results demonstrate that the connection between comets and asteroids is a lot closer than we think. Asteroids have demonstrated other comet-like “behaviours” but this is the first time that water has been detected.

The water vapour ejected is mostly lost to space with only one fifth returning down to the surface. The discovery of water vapour on an asteroid contributes to our understanding of how different planetary bodies may move around the solar system. The asteroid belt marks the snow line within our solar system, or the distance from the Sun at which ice can form. Asteroids closer to the sun than this line are usually rocky and dry, and the ones further out are icy. The identification of an icy asteroid at the snow line implies that bodies which form further out in the solar system are capable of inward migration. If this process occurred during the formation of the Earth and other planets, then these icy bodies could have brought with them water and organic molecules, with obvious implications for planetary evolution and the origin of life on Earth.