The clever scientists at MIT have suggested that Mercury may have once had a large sea of magma on it’s surface. They propose that it developed sometime soon after it’s formation over 4 billion years ago.
The proposal is from the initial findings of a group of scientists who investigated the XRay data from NASA’s Messenger craft and noticed that there were two different types of rock on the surface of the planet. They then used the data to create the two rock types in their laboratory.
These samples where then subjected to various tests designed to simulate the geological effects that would have probably happened to those on the planet. They then did some clever stuff with investigating the chemical ratios like Magnesium oxides and oxides of silicon and aluminium.
After cooling the samples they then took a selection of crystals for even more analysis. They wanted to determine situations where the original rocks might be related however this proved to be rather difficult. They determined that the two compositions produced were simply too different to have been created from the same region of the planet.
The hypothesis is that these two very different regions were created by a large ocean of magma. This would have formed very different compositions of crystals as it cooled and solidified. The ocean would then have melted a second time and then poured lava onto the surface with a huge volcanic display.
There are some great pictures of such volcanoes and the surface of mercury on the NASA website. For some reason access to these were blocked from certain countries of the world. I found this website which helped me gain access on my Ipad – using a VPN on an Ipad, you might not need these though depending on your location.
Here’s a video explaining the process too –
