What's up with the strange colors of these dunes? Mars isn't really blue and gold, it's just that this picture was taken in infrared wavelengths to better show the composition of the sand here. But these dunes, known as "barchans," would look striking in any light: they often form cool horns or notches on their steep leeward sides.

Though they look like tree rings, these formations are actually layers of bedrock in a small crater inside of Schiaparelli Crater. In some places, a dark sand covers the layers, sitting atop ridges that no one is quite sure how to explain.

The curvy lines seen here form what is called "brain terrain." It forms atop ice at the base of a small hill, though scientists still don't know exactly why it creates this cantaloupe-like texture.

Mars is so cold that frozen carbon dioxide, or dry ice, remains from season to season at is south pole. The white areas of this image are this residual dry ice cap while the darker parts are water ice with dust and particles trapped in it. As to why that formation on the lower right looks like North America, who knows?

Water is thought to exist in large deposits beneath the Martian surface. When it disappears, the ground sinks and creates scallop-shaped depressions and polygonal troughs. The formations are known as "thermokarsts," a variety of which can be seen here.

The ceaseless winds of Mars create sand dunes all across its surface. But beneath these dunes in Syria Planum are bright deposits with steep faces and sharp, weathered ridges. These lower deposits are evidence that in Mars' past the winds were much more ferocious.

At first glance, you might mistake this for a close-up of human skin. It's actually a bunch of polygonal shapes that would normally indicate some sort of subsurface water processes. Instead, scientists realize that they are simply intersecting sand dunes.

One of the best images from Mars ever taken was a 2009 pic showing the tracks of dust devils on the sand. HiRISE here provides an updated shot of the same area, showing completely different tracks, indicating that at least one dust storm has wiped the slate clean in the meantime and new dust devils have run over the ground.

These odd and tortured raised ridges both look strange and leave scientists without any good explanation as to how they formed. Some say they might have been left behind by an ancient ocean or perhaps ancient glaciers. For now, the formations remain a mystery.