A close-up view of Mercury
New observations from a spacecraft orbiting Mercury have revealed that the tiny, pockmarked planet harbors a highly unusual interior — and the craft’s glimpse of Mercury’s surface topography suggests the planet has had a very dynamic history. The observations were taken by a probe called MESSENGER (short for Mercury Surface, Space Environment, Geochemistry and Ranging), the first ever to enter orbit around Mercury. MESSENGER reached Mercury’s orbit in March 2011, and has since circled the planet twice a day, collecting nearly 100,000 images and more than four million measurements of Mercury’s surface. A team of scientists from institutions including MIT, the Carnegie Institution of Washington, Johns Hopkins University’s Applied Physics Laboratory and NASA’s Goddard Space Flight Center have analyzed the data and precisely mapped the planet’s topography and gravitational fields. From the gravity estimates, the team found that Mercury likely has a highly unusual interior structure — an exceptionally large...