It is now generally agreed by scientists that liquid water used to exist on Mars, and that liquid contributed to some of the geological features that we can still see on the surface of Mars today. But there is no liquid water on Mars now, and even the amount of liquid water that remains in the polar ice caps on that planet are not enough to explain all the water features we see. Where did it go? Space.com had an article this week that describes some new research based on data taken from the Mars Curiosity rover, which found evidence of rising and falling water levels in some of the Martian geology. You can read more and see some images showing how the water levels changed in one location here.
