The MESSENGER (MErcury Surface Space ENvironment, GEochemistry, and Ranging) spacecraft has found strong evidence both for water ice and organic molecules in shadowed craters near Mercury’s poles. Unlike Earth, Mercury has no seasons: its axis stands perpendicular to its plane of orbit, so deep craters near the north and south pole will have bottoms in permanent shade. Any place else on the surface will eventually be exposed to the Sun’s punishing glare, not only melting ice but boiling away any residual water. However, during the early Solar System, meteorites and comets brought water and organic compounds to the planet’s surface—at least according to planet formation models. This new discovery lends strong support to that theory.

The results from both the reflection and neutron analyses were consistent: several craters in Mercury’s polar regions provide sufficient shadow for stable water ice. The large craters named Prokofiev and Kandinsky were both found to contain significant radar-bright (RB) patches, indicating highly reflective materials. (Craters on Mercury are commonly named for famous artists, authors, composers, and the like. As a fan of both Prokofiev and Kandinsky, I approve.)

The size of the reflective patches matched the total proportion of each crater that lies in permanent shadow. [Read more…]

MESSENGER: Mercury’s craters have ice and organic molecules