The surface temperature of Mercury swings between -180 ºC and 425 ºC (-292 ºF and 797 ºF). Most of the surface is scorched from being so close to the sun, but there are craters on Mercury’s poles that are permanently in shadow, which makes them “cold traps” where the temperature is always freezing from the lack of sunlight or enough of an atmosphere to provide ambient heat.
Now NASA’s Messenger probe — the first spacecraft to orbit Mercury — has found evidence that these cold traps may contain frozen water that’s been sitting in these craters since the the planet formed. Last year, the Arecibo Observatory found patches near Mercury’s poles which strongly reflected radar in a way similar to ice. Then Dr. Nancy Chabot and others at the Johns Hopkins University Applied Physics Laboratory (JHUAPL) lined up that data with the topographical map of Mercury’s south pole — the first map of its kind — created by the Messenger probe. The result is pictured above: the yellow areas which seemed to be ice lined up with all of those shadowed craters.
Dr Nancy Chabot explained, “We’ve never had the imagery available before to see the surface where these radar-bright features are located. [...] MDIS images show that all the radar-bright features near Mercury’s south pole are located in areas of permanent shadow. [...] Near Mercury’s north pole such deposits are also seen only in shadowed regions, results consistent with the water-ice hypothesis.” However, she cautions, this does not constitute proof, and for many craters, icy deposits would need to be covered by a thin layer (10-20cm) of insulating debris in order to remain stable. [BBC]
NASA recently announced Messenger’s mission will be extended to 2013, so we’ll have more time to figure out if Mercury really has ice and if the planet is, as has been long speculated, equivalent in size to yo mamma.