NASA has discovered tracks on Mars, but they weren't left there by aliens or Elvis. The Mars Reconnaissance Orbiter peered down to the Red Planet's surface in the middle of July and spied a strange dotted path left by a rather large tumbling rock.
The path looks like it could have been laid down by a very large bird. The irregularity is due to the odd shape of the boulder itself. It's oblong and ended up landing upright when it finally came to rest. The total length of the trail is one-third of a mile. The boulder itself is over 11 feet wide. Calculating by its shadow, NASA estimates it's about 20 feet tall.
The boulder is located in an area of Mars where the slopes are steep, the sort of place where a rover like Curiosity isn't too likely to roam. The image was captured by the orbiter's High Resolution Imaging Science Experiment (HiRISE) camera.
The image of the boulder and its trail is fascinating for the reminder that the seemingly unchanging surface of Mars is subject to some of the same forces of nature we deal with on Earth. If we someday manage to land a human settlement on Mars, we may want to send along a few yellow "watch for falling rocks" signs.