The Martian surface has undergone dramatic changes in the last few years with the appearance of new gullies and fresh boulder tracks, new images show.
The photos, taken by the orbiting Mars Global Surveyor spacecraft, suggest that the Red Planet is perhaps more active than previously thought.
The spacecraft, in its ninth year in orbit, spotted two fresh gullies on a Martian sand dune that were not present in 2002. Scientists think the gullies might have formed when frozen carbon dioxide trapped by windblown sand vaporized, releasing gas that allowed the sand to flow freely.
The spacecraft also took images of boulder tracks at another site that were not there two years ago. The tracks were probably caused by dozens of boulders rolling down a slope from strong wind or a quake, scientists said.
Researchers also noted that impact craters forming since the 1970s suggest that crater-formation is a slow process, occurring at one-fifth the pace previously thought.
The pace is important because it is used to estimate the age of Martian surfaces, officials said.