In astronomy we are used to things not changing. There is the occasional comet or supernova or gamma-ray burst to liven things up, but most of the time a galaxy or star looks the same today as it did over 100 years ago. Most things just don't change over human lifetimes.
A recent press release from NASA's Mars Global Surveyor team reveals changes on Mars that have occurred just over the last few years. Gullies carved by evaporating dry ice appear in sand dunes, the southern polar ice cap changes shape from winter to winter, and even a meteor crater appears out of nowhere and then fades from view.
These pictures tell us that Mars is an active planet like the Earth, not a slow-changing world like the moon. This isn't surprising, as humans have seen huge dust storms appear on Mars and observed the changing polar caps for centuries. But to see the changes up close is, in scientific parlance, wicked cool.