A recent experiment conducted by MIT researchers has led some experts to believe an ocean of lava may have been flowing on Mercury's surface some four billion years ago. The finding came as scientists feverishly analyzed data from NASA's Messenger probe, which has given them some of the best insight into Mercury's composition. The presence of two vastly different types of rock on the planet was a curious discovery, and led the MIT team to create an experiment that would hopefully point to a geographical process responsible for the disparity. Researchers recreated the rocks in a lab and exposed both to a variety of temperatures and pressures. “You can tell what would happen as the melt cools and crystals form and change the chemical composition of the remaining melted rock,” said Timothy Grove, a geology professor at MIT. “The leftover melt changes composition.”
Ultimately Grove and his associates concluded that the two rock compositions couldn't have come from the same region, leaving the so-called "lava ocean" as the only viable explanation. If magma did at one point cover some of Mercury's surface, it was a long time ago. “The crust is probably more than 4 billion years old, so this magma ocean is a really ancient feature," Grove said. Specifically, he estimates that the ocean would have been flowing sometime within the first one million to 10 million years of Mercury's existence.