This is really neat.

I wonder how they know it's H2O specifically? Wouldn't it be great to get a sample?

It's so amazing that just a few decades ago, we were only just discovering that the red shsdows on the surface weren't canals. Now we have google Mars. Being another planet up so close still seems really freaky,when you look at the picture, and then look at the sky, and think being close only gives you more to think about. Nature keeps showing us things that mean we have to reconsider what we think we know, but nature can do it in such a beautiful way we almost get excited when we find out we're wrong. It usually means we've found something more important.