The Zhurong rover provides proof that this region of Mars was covered by an ocean!

Even inactive, the Chinese rover Zhurong continues to be talked about. It would indeed have provided the long-awaited proof that an ocean indeed occupied the boreal region of Mars 3.6 billion years ago!

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[EN VIDÉO] Zhurong: his first sounds on Mars Zhurong is the first Chinese rover to set foot on Mars. And on the 27th…

Mars the red could well have been blue in the distant past. This is at least what the observations reported by the Chinese rover Zhurong suggest. They come to support a hypothesis put forward several decades ago about the past existence of a boreal ocean on the planet. A hypothesis which, until now, was sorely lacking in data collected in situ.

And that was one of Zhurong’s missions. Collect evidence to confirm or refute the presence of an ancient ocean on Mars. The rover’s landing site has indeed been finely chosen to achieve this objective. In 2021, Zhurong thus landed at the southern end of Utopia Plain, in the northern hemisphere of the planet, at what was then interpreted as an old coastline.

Sediments That Bear Weird But Telling Marks From Mars’ Past

During its journey of almost two kilometers, the rover collected all kinds of information, in particular thanks to its multispectral camera MSCam, allowing a better understanding of the nature of the ground in this region. Zhurong thus studied in detail a geological formation named Vasitas Borealis. Its cameras produced 106 panoramic images that allowed scientists to study the surface morphology and structural characteristics of exposed rocks along the rover’s path.

The results were presented in an article published in the journal National Science Review. And there, surprise! The images relayed by the rover show that the rocks are finely structured and record a well-known pattern on Earth. These are not volcanic rocks, so common on the surface of Mars, but sedimentary rocks with oblique laminations. The outcrops studied are in fact structured by different sedimentary units which are made up of oblique striae. The orientation of these streaks (we speak of laminations) is however opposed between each unit. This organization is indicative of a particular dynamic in sediment deposition: it indicates a bidirectional flow that is not associated with aeolian formations, like most of the dunes currently observed on the surface of Mars. On Earth, these oblique laminations whose direction alternates regularly are indeed typical… of a shallow marine environment subject to the action of the tides!

A current that goes one way, then the other

When the tide rises, the current arranges the sediments in the form of small ripples which are built as they progress towards the coast. In section, we will therefore observe laminations sloping towards the ocean. During the ebb tide, on the contrary, new ripples of sediment will be deposited on the previous ones, but progressing this time towards the ocean. In section, we will therefore observe, for this sedimentary unit, oblique laminations sloping towards the coast. The entire stratigraphic column thus shows fine sedimentary units with alternating orientations of oblique laminations. This is exactly the configuration observed on Mars in the formation of Vasitas Borealis ! But Zhurong’s observations make it possible to go even further in paleoenvironmental analysis.

At the base of the stratigraphic column (the oldest part), there are indeed sediments without laminations, indicating a calm deposit environment, not subject to the action of the tides. On the top of the column (the youngest part), on the contrary, we observe non-planar units, whose intersecting trough shape is typically associated with the development of small channels crossing each other over time. The superposition of these units (planar, laminated, then trough) therefore testifies to an evolution of the coastal environment of this paleo-ocean, and more particularly to a marine regression (relative drop in sea level).

These discrete sedimentary structures are therefore extremely rich in information and provide proof that an ocean indeed occupied the boreal region of Mars 3.6 billion years ago. An essential result for the restoration of the planet’s past and the search for potential traces of life.