High resolution images of Mars.

That's right. But that is not all; copyright free high resolution images of Mars from the HiRISE instrument on the Mars Reconnaissance Orbiter. Over 40.000 of them. Huge camera nerd and want to know more about the camera specs? I got you

And if you're using iOS 9 and wondered what the default wallpaper was? Exactly, a sand dune on Mars. Actually, the first image in their backgrounds is HiRISE's, as well as the second and third. Wonderful. :)