These might look like trees on Mars, but they're not. Groups of dark brown streaks have been photographed by the Mars Reconnaissance Orbiter on melting pinkish sand dunes covered with light frost. The image was taken near the North Pole of Mars, spring 2010. Objects about 25 centimetres across are resolved on this image, which is about one kilometre wide. Close ups of some parts of this image show billowing plumes indicating that the sand slides were occurring at the time of the photo; see center left.