Some of you have noticed this image I took on Mars. Sure, it may look like a tiny door, but really, it’s a natural geologic feature! It may just *look* like a door because your mind is trying to make sense of the unknown. (This is called "pareidolia") http://go.nasa.gov/3sGhC8l 

Here’s a zoomed-out view with the feature circled. In it, you see a small crevice (>30 cm tall) between 2 fractures in a rock. There are several linear fractures in the mound - but in this spot, several fractures intersect, which allowed the rock to break at such sharp angles.

In a less literal sense, my science team is interested in these rocks as a “door” to the ancient past. As I climb up this mountain, I’m seeing higher levels of clay give way to salty minerals called sulfates – clues as to how water dried up on Mars billions of years ago.