ケレスの最も暗い場所で検出された水氷

Water ice exists in regions of perpetual darkness on the surface of the dwarf planet Ceres, reveals a paper published online this week in Nature Astronomy.

Ceres is the third planetary body, after the Moon and Mercury, where water ice has been detected in permanently shadowed areas. The presence of water on Ceres was detected from Earth in 2014 and confirmed by the Dawn spacecraft that has been orbiting the dwarf planet since March 2015. Areas where the Sun never shines are natural places to look for water ice, as they can trap water molecules at geological timescales.

Thomas Platz and colleagues processed images of the craters in the northern polar region of Ceres that were taken by the Dawn Framing Camera. They found locations of perpetual shadow in more than 600 craters, 10 of which exhibit bright features. Spectroscopic analysis confirms the presence of water ice in these features.

The relatively small number of locations with these bright spots, compared with Mercury where the permanently shadowed regions are filled with water ice, can provide insights into water availability on Ceres and how the trapped ice is dispersed, by impacts for example. Moreover, the authors note that this discovery shows that ice becoming trapped in shadowed regions is a common process on airless bodies of the Solar System.

The American Geophysical Union will hold a press conference about the findings described in this paper on Thursday, December 15, at 10:30 a.m. PT/1:30 p.m. ET at the 2016 AGU Fall Meeting in San Francisco. More information can be found on the 2016 AGU Fall Meeting media center.