The question of how Mars changed from a once wet world to the much colder and drier one we see today is one that scientists have been trying to answer for a long time. There is plenty of evidence that Mars use to have lakes and rivers, and perhaps even oceans. But what happened to change that? Now, a new study might bring us one step closer to solving this conundrum.
The fact that Mars used to have large amounts of liquid water on its surface is pretty much accepted among scientists, but there is still the question of how long that water lasted. How long ago was it still present? A billion years? A few million? New evidence based on data from the Mars Reconnaissance Orbiter (MRO) suggests that water was still on the surface within the past million years, perhaps even as recently as 500,000 years ago, which is indeed recent, geologically speaking.
When the topic of ice on Mars comes up, the first thing that usually comes to mind are the polar ice caps which are prominent even in small telescopes. There is, however, ice elsewhere on the planet as well, such as beneath the surface in the mid-latitudes, covered by dust. Now, a new study has revealed the extent of these subsurface glaciers and the amount of frozen water they contain.
This is interesting, a recent HiRISE photo from the Mars Reconnaissance Orbiter spacecraft showing an oval pit or crater with an opening in the bottom (cropped here from one of the larger images) near Galaxias Chaos on Mars. The opening is also oval, and you can see some sand dunes on the bottom. How did it form? More images are available here.