ESA has published a photograph of a sort of labyrinth that is part of a region called Adamas Labyrinthus on Mars taken by the Mars Express space probe. This region is in turn part of Utopia Planitia, a huge impact basin with an estimated diameter of about 3,300 kilometers. The fractures in Adamas Labyrinthus create a system of polygonal shapes that might have originated from fine-grained sediments that were once at the bottom of an ocean.
The connection with a possible ancient ocean in the region that includes Adamas Labyrinthus comes from the fact that fine-grained sediments such as mud are deposited in water masses such as oceans. On Earth there are formations that are similar from a morphological point of view but also in size, with ranges between 5 and 20 kilometers in diameter, which are formed by the movement of sea water.
The polygons are formed by graben up to two kilometers wide running back and forth. They might have been extended over time after their formation due to the tectonic activity existing in the region and the progressive sublimation of the buried ice.
Some of the Adamas Labyrinthus graben show dark deposits that extend along their top edges. Those could be emerging layers of fine-grained ashes which are the source of the black sand dunes widespread on Mars. A relevant fact is that these dark lines mainly occur on the side of the slope facing the Sun.
The consequence is that scientists believe that the emergence of ash layers from under the layer of ice, debris and dust that covered them was facilitated by solar irradiation. The ice sublimated on the heated slopes allowing that layer, which was no longer held in place, to slip off or being consumed. Eventually, the result is that the ash layer appeared.
It’s interesting that a few weeks ago a study was published describing the discovery of a huge underground ice deposit at Utopia Planitia. According to the authors, it was probably formed by the accumulation of snow in a period of Mars’ history when the planet’s axis was more tilted. How to combine this study with the presence of an ancient ocean?
If there really was was an ocean at Utopia Planitia, it existed a few billion years ago, when the environmental conditions on Mars were more similar to those on Earth. When the atmosphere became thinner, liquid water evaporated so it’s possible that the Utopia Planitia basin got emptied until it got filled by the ice present today. Ocean traces could have been left somewhere and photographed by the Mars Express space probe’s High Resolution Stereo Camera (HRSC) instrument. It’s one of the points of the long and complex history of Mars that need clarification.