It’s said that “art imitates life,” but how about baked goods imitating geologic formations! Strange as it might seem, the MESSENGER spacecraft that has been orbiting the planet Mercury since March, 2011 has discovered unusual groups of ridges and troughs that do just that – imitate a common baked-good, a pie. Families of extensional troughs or graben revealed by MESSENGER are encircled by contractional wrinkle ridges arranged in circular rings. This pattern of ridges and troughs resembles the raised edge and cracks in a pie crust. But the analogy with “pie crust” doesn’t stop there. These families of landforms are directly associated with “ghost” craters, impact craters that have been flooded and buried by lava flows. The rim of the buried impact crater concentrates the contractional forces that forms a ridge ring, revealing the outline of the buried crater. So, to complete the analogy the impact crater is the pie pan. We think the troughs or graben form from cooling and contraction of unusually thick lava flow units, like the custard filling cools in a pumpkin pie. It is the eruption and rapid accumulation of very fluid lava flows into thick cooling units in combination with global contraction from cooling of the interior of the planet that may explain why these families of tectonic landforms in ghost craters on Mercury have not been seen elsewhere in the Solar System.
Dr. Tom Watters is a geologist in the Center for Earth and Planetary Studies at the National Air and Space Museum.