Cool image time! In the most recent download of new images from the high resolution camera of Mars Reconnaissance Orbiter (MRO) were two photos, found here and here, that struck me as very intriguing. Both were titled simply as a “Terrain Sample” image, which generally means the picture was taken not because of any specific request by another scientist doing specific research but because the camera team needs to take an image to maintain the camera’s proper temperature, and in doing so they try to time it so that they can do some random exploring as well.

As it turned out, the two images were more than simply random, as they both covered different parts of the same Martian feature, what looks like a branching dry dendritic river drainage. Below is a mosaic of those two images, fit together as one image, with a wider context image to the right, taken by Mars Odyssey, showing the entire drainage plus the surrounding landscape with the white arrow added to help indicate the drainage’s location.


For the full images go here and here for the two MRO pictures, and here for the Mars Odyssey picture.

The assumption we Earthlings instantly make when we see such features on Mars is that they must have been formed by flowing water. In fact, this is the assumption that planetary scientists have been basing much of their geological research on for the past half century, since Mariner 9 first reached Mars in 1971 and took the first photographs of numerous such channels.

The problem the scientists have had is that because of Mars’ thin atmosphere and cold temperatures, they have so far have been unable to construct any model that allows liquid water to flow on the planet’s surface, even in the far past when it is thought the Martian atmosphere might have been thicker. No hypothesis seems satisfactory or even very believable.

So, did flowing water cut these canyons into this Martian plateau? Maybe, but good science requires one to consider unexpected possibilities. For example, the large crater to the east of this canyon in the wide context image appears to have an circular plateau partly filling its interior. This location is at 41 degrees north latitude, and based on research compiled in the past decade scientists now believe there are many buried glaciers at this latitude, the bulk of which are found inside craters and are called concentric crater filled glaciers. That plateau in that big crater certainly suggests the presence of a buried glacier, as it resembles many such glacial filled craters.

Thus, there are likely glaciers in this region, which means there is also likely a lot of buried ice.

Many scientists now think that the Martian climate goes through major cycles as the planet’s obliquity (the tilt of its polar axis) changes over time. Unlike Earth, that tilt on Mars shifts much more, from 11 to 49 degrees [pdf]. When that tilt is low, the poles are colder than the mid-latitudes, so any ice in those mid-latitudes sublimates away to fall as snow at the poles. When the tilt is high, the mid-latitudes are colder than the poles, so the icecaps begin shrinking, their ice now shifting back to the mid-latitudes to fall as snow and thus produce many active glaciers.

At this moment, with Mars’ tilt at 25 degrees, it appears that things are in a steady state. Data suggests the poles are not shrinking, and the glaciers at the mid-latitudes are both not active and somewhat stable.

However, in the past, when that tilt was high, snow would have been falling over the channels in today’s image, and there would have been active glaciers in these canyons. One can’t help wondering if glacial flow, not liquid water, might have done most of the carving of these channels.

One last point that will only add to the mystery. This location is on the very edge of the transition zone between the southern cratered highlands, sitting very close to the northern lowland plains where some scientists think an intermittent ocean might have once existed. At that edge there is a lot of evidence of a variety of shoreline features, as if it had once been the edge of a sea had had waxed and waned. This particular region has lots of such channels, all suggesting water flow.

If glaciers were the cause, not water, scientists will have to explain all these features suggestive of water flow. This will not be easy, as it will likely require a complete rethinking of glacial geology. In Mars’ low gravity glaciers might be able to do many of the same things that water does on Earth, and might be able to create features that to us Earthlings, coming from this water planet, think were created by water.

Or not. Such a conclusion requires a lot of complicated rethinking, and in science picking a complex solution is usually a mistake. At the same time, if the data demands a different answer, you need to look for it.