January 22, 2014
ESA’s Herschel space observatory has discovered water vapour around Ceres, the first unambiguous detection of water vapour around an object in the asteroid belt.
With a diameter of 950 km, Ceres is the largest object in the asteroid belt, which lies between the orbits of Mars and Jupiter. But unlike most asteroids, Ceres is almost spherical and belongs to the category of ‘dwarf planets’, which also includes Pluto.
It is thought that Ceres is layered, perhaps with a rocky core and an icy outer mantle. This is important, because the water-ice content of the asteroid belt has significant implications for our understanding of the evolution of the Solar System.
When the Solar System formed 4.6 billion years ago, it was too hot in its central regions for water to have condensed at the locations of the innermost planets, Mercury, Venus, Earth and Mars. Instead, it is thought that water was delivered to these planets later during a prolonged period of intense asteroid and comet impacts around 3.9 billion years ago.
While comets are well known to contain water ice, what about asteroids? Water in the asteroid belt has been hinted at through the observation of comet-like activity around some asteroids – the so-called Main Belt Comet family – but no definitive detection of water vapour has ever been made.
Now, using the HIFI instrument on Herschel to study Ceres, scientists have collected data that point to water vapour being emitted from the icy world’s surface.
“This is the first time that water has been detected in the asteroid belt, and provides proof that Ceres has an icy surface and an atmosphere,” says Michael Küppers of ESA’s European Space Astronomy Centre in Spain, lead author of the paper published in Nature.
image credit: ESA/ATG Medialab