The solar system’s smallest and innermost planet has come into greater focus than ever before. Though only halfway through its first year in orbit around Mercury, NASA’s MESSENGER spacecraft has already revealed that the planet possesses a much more dynamic and fiery past than previously imagined.

“The data obtained by the MESSENGER imaging system in a mere few months has revolutionized our thinking about volcanism on Mercury,” said geologist James Head of Brown University, a member of the spacecraft’s science team, during a NASA press briefing today. The team also published a set of seven papers in the journal Science with their new findings.

Mercury is the densest of all the planets in the solar system, and is composed of around 60 percent iron — twice as much as Earth. How any why it ended up with so much iron is one of the planet’s main mysteries. Learning more about its formation and early history may give researchers a better understanding of both our own solar system and those around other stars.

In the past, scientists were unsure how much of Mercury’s surface was shaped by volcanism. Flybys with the Mariner 10 spacecraft in the 1970s could not definitively conclude whether formations on the surface were due to volcanic activity or impacts from craters. But now, with MESSENGER in orbit, the details of this tiny planet are finally in view.

Above:

The crater Debussy's long radial rays formed when an asteroid impact sent ejecta flying from the crater in all directions, forming secondary craters and uncovering younger terrain. Because of its brightness, Debussy is thought to be a relatively young crater, because the solar wind causes the planet’s surface to darken over time. MESSENGER is revealing that both impacts such as this and volcanic activity have been important in Mercury’s history.

Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington