Mars clearly had a watery past and much of the water is expected to still be on the planet. Finding out where the ice is hiding could tell us a lot about the planet’s climate history and something about Mars’ current water cycle. It could also help direct future landers to sample the planet’s water and potentially use it to support human landings.
While we found a lot of ice near the pole during the Phoenix Lander mission, that’s not a very convenient location for future landings (in part because that pole’s location was frozen over with dry ice during the Martian winter). In today’s issue of Science, researchers report the likely presence of ice sheets in more temperate regions. The plates are at least 100 meters thick and seem to retain layers that can help us reconstruct how the water has frozen there.
MRO data
As with many things on Mars, the work is based on data from the Mars Reconnaissance Orbiter. It has a variety of instruments that can examine the chemical makeup and subsurface structure of Mars, along with the best camera we’ve ever sent to another planet. Over the years, MRO has built up an extensive catalog of features on the surface of Mars, many of which have been imaged from multiple angles.
Analyzing these features with a filter that accentuates colors, a team of researchers noticed something remarkable about the Red Planet: some of them had a striking blue color. They were found at mid-latitudes (about the Mars equivalent of Canada or the UK) and occupy poles-facing slopes. The slopes appear to be the product of erosion along the edges of a broad, smooth elevated plain. Spectrograph imaging provided evidence of water on the Martian surface in the region, reinforcing the idea that this could be ice.
The bluish slopes were quite steep, with a slope approaching 55 degrees in some cases. Their lower reaches were covered in debris, making it difficult to determine the total thickness of any ice deposits. But whatever it is, it’s over 100 meters thick and probably at least 130 meters. That’s thick enough for the rotating camera to dissolve different colored bands in the material. That suggests the bands have settled over time, pinning down different periods in Mars’ history. A lack of craters indicates that some of that history could be quite recent.
The authors favor the idea that what they found is indeed ice, likely mixed with dust, and deposited at a time when Mars experienced snow. “The presence of stripes and color variations suggest layers,” they argue, “possibly set off with changes in the proportion of ice and dust under different climate conditions.” So examining the layers could tell us about the history of how Mars’ watery past came to an end.
lots of ice cream
Currently, the ice sheets appear to be covered with a very shallow layer of dust that has frozen in place — the authors estimate it to be less than two meters thick. The slopes are likely constantly exposed as the ice sublimes in the Martian atmosphere, likely cycling to the poles and getting frozen there. The researchers estimate that this causes the loss of about a millimeter per year, suggesting that the ice sheets were once significantly larger than they are now.
These visible ice sheets are probably only a small representative of the total water ice on Mars. Radar studies of the subsurface have found features interpreted as dust and rock-covered glaciers and some clues to ice sheets in other parts of the Red Planet. But, of course, it’s difficult to confirm the identity of the layers seen in radar returns, and the instrument doesn’t have the resolution to figure out how close the ice is further than “less than 20 meters” to the surface.
So if these slopes still look like ice after closer inspection, they seem like a great location to study the history of water on Mars. They could also create accessible sites to extract water for human use, although that would obviously run counter to studying the ice sheets for clues to the past.
Science2017. DOI: 10.1126/science.aao1619 (About DOIs).