Mars has two dinky moons, Phobos and Deimos. Phobos is the bigger of the two, and is about 22 kilometers (13 miles) across. There have been hi-res images of Phobos taken in the past, but none like this!
That's the creepily good HiRISE camera from the Mars Reconnaissance Orbiter, of course, that took the image. Click it to embiggen and get much higher-res versions: the raw data has a resolution of 7 meters per pixel. That's smaller than a house. There have been more detailed images taken in the past, but these collected more light from the tiny moon and so have better quality.
The detail is remarkable. The image is false color, and blue may represent fresher material.
The crater Stickney on the right is huge compared to the moon; if the impactor had been any bigger or moving faster it would have shattered the moon. The long parallel grooves were probably formed as stress fractures in the impact. Check out the awesome image of the crater itself. Wow.
And if that's not enough, pull out your red/green glasses and take a gander at the 3D anaglyph they made. The tiny craters really stand out... uh, I mean, stand in. Whatever. They're cool, so take a look.
And do it while you can. Eventually Phobos will crash into Mars, and that'll be that. Chances are that by then we'll boost it to a higher orbit ourselves (it makes a handy base), but still. Coolness prevails on Mars.
Hat tip to BABloggee and HiRISE guy Timothy Reed, who tells me he "lovingly installed and aligned all the optics".