With all the excitement surrounding the Mars Rover this year, people may have forgotten that our solar system is home to seven (sorry Pluto!) other planets. Nonetheless, the recent discovery (detailed in this Science paper) of organic material and ice in the polar craters of Mercury is sure to put this small planet in the spotlight, at least for now.

As the closest planet to the sun, Mercury is certainly no stranger to light and the blistering heat that come with it. Because the craters at its poles are shrouded in shadow though, temperatures there are much lower than the average for Mercury. This has created a cold enough environment for large ice deposits in these craters, as indicated by remotely collected data from MESSENGER, the NASA spacecraft orbiting Mercury. Through measurements of surface reflectance with laser altimetry, scientists have determined the existence of bright and dark regions in the polar craters. The bright regions correspond to sheets of ice, while the darker areas are thought to be deposits of organic volatiles covering a layer of pure ice underneath. This hypothesis is further supported by results of neutron spectroscopic analysis of Mercury’s polar craters.

So far, the organic material seems to contain compounds like methane and ethane, and is similar to tar in consistency. Researchers believe the organic material and water arrived on the planet with the impact of comets or asteroids, and that over many years, these substances collected in polar craters where they would be shielded from the sun’s radiation. Unfortunately, this theory does not provide evidence for the existence of life on Mercury, but it might suggest a similar “delivery” of organic material to Earth in its distant past. Who knows, perhaps the building blocks for life on our own planet came from a collision-bound asteroid as well.

