Mercury’s hidden ice content discovered

Research carried out at Brown University in the US suggests more ice is present than originally thought on Mercury.  

Poring over data collected by NASA’s MESSENGER probe, the scientists discovered three new craters near Mercury’s North Pole that appear to have large surface ice deposits. The researchers also discovered a number of smaller deposits in the same region, either in craters or the shadowed area between them.

The search for water

Ariel Deutsch, the leader of the study published in Geophysical Research Letters, said: “The assumption has been that surface ice on Mercury exists predominantly in large craters, but we show evidence for these smaller-scale deposits as well. Adding these small-scale deposits to the large deposits within craters adds significantly to the surface ice inventory on Mercury."

Deutsch, along with Gregory Neumann from NASA, looked at results from readings collected by the probe’s laser altimeter. This device is mostly used to map elevation but can also record surface reflectance, indicating surface ice on the planet, helping scientists to discover them.

The scientists discovered patches smaller than the crater-based deposits, but large enough to resolve with the altimeter. They located four, all with diameters less than five kilometres. Deutsch said: “These four were just the ones we could resolve with the MESSENGER instruments. We think there are probably many, many more of these, ranging in sizes from a kilometre down to a few centimetres."

It is still unknown how polar ice found its way to Mercury. The currently accepted hypothesis is that it was delivered by a water-rich comet or asteroid impact. Another theory is that hydrogen may have been forced into the surface by solar wind, combining with an oxygen source to form water.

Professor Jim Head, also from Brown University and co-author of the study, said: “One of the major things we want to understand is how water and other volatiles are distributed through the inner solar system — including Earth, the Moon and our planetary neighbours. This study opens our eyes to new places to look for evidence of water, and suggests there is a whole lot more of it on Mercury than we thought.”