Ancient volcanic explosions shed light on Mercury's origins

Mercury was long thought to be lacking volatile compounds that cause explosive volcanism. That view started to change when the MESSENGER spacecraft returned pictures of pyroclastic deposits--the telltale signature of volcanic explosions. Now more detailed data from MESSENGER shows that volcanoes exploded on Mercury for a substantial portion of the planet's history. The findings suggest Mercury not only had volatiles but held on to them for longer than scientists had expected.