This is a pretty spectacular find. While it doesn't mean that we'll find cities with flying Martian cars or anything like that, we've been steadily paring back our expectations for Mars. First we hoped to find life, then just water, then just permafrost, then evidence of water millions of years ago. But now comes evidence that new gulleys have been carved out within the past five years. That's surprising since water is not stable at Mars' surface.

By the way, side-by-side comparison photos are included.

(And yes, I know this is a week old.)