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[EN VIDÉO] On Mars, the delta of Jezero Crater. This panorama of the Jezero Crater delta is the work of the onboard Mastcam-Z…
A few months ago, the Zhurong rover finally provided in situ evidence that there was indeed an ocean in Mars’ northern hemisphere 3.6 billion years ago. Evidence supported by new results published in the journal Icarus, based on a completely different approach.
In fact, Mars’ gravity field was used here to support the hypothesis of the previous existence of a huge Martian ocean. Surprised? Not very much. It has long been known that Earth’s gravity field exhibits “variations” compared to what would be expected from a homogeneous Earth model. These diverse “gravity anomalies” reflect the heterogeneity of the planet at different scales. Gravimetry is therefore a geophysical discipline that has contributed significantly to refining our understanding of the Earth’s internal structure.
Gravimetry for understanding Mars’ past
Of course, if gravimetry was developed on Earth and to understand the Earth, our planet is not the only star on which this method can be applied. Scientists now have enough data to use it to study the moon and Mars.
However, the methodology used by the research team led by Jaroslav Klokočník from the Astronomical Institute of the Academy of Sciences in the Czech Republic differs slightly from the usual approach to mapping magnetic anomalies.
Gravity anomalies actually arise from defects or excess mass compared to the reference model used. For example, compared to a featureless Earth model, the presence of a mountain represents an excess of mass, illustrated by a positive gravity anomaly. An ocean, on the other hand, is represented by a negative anomaly because water has a lower density than rock.
An innovative approach that is more comprehensive than simple severity anomaly analysis
The approach developed by researchers to study Mars is based on the term “gravitational aspects”. This approach is intended to be more comprehensive than simply considering gravity anomalies. In fact, gravity aspects take into account not only gravity anomalies, but also other parameters mathematically derived from the gravity signal, which represent a rich source of information that allows a more precise characterization of the source of the anomaly.
This approach has already been tested in North Africa to identify the shore of an ancient lake and the traces of ancient rivers that have now disappeared in the sands of the Sahara. Results supported by archaeological data supporting the former presence of a lake at this site. Thanks to this method, researchers were able to compare the gravitational aspect of Mars with that of Earth. The results of the gravimetric analysis are therefore consistent with the hypothesis of a past ocean in the boreal region of Mars.
Although this method does not provide irrefutable proof of the past existence of this ocean, the innovative approach lends credibility to recent discoveries, particularly by the Chinese rover ZhurongZhurong.
In a recently published study, American geologist Lorena Moscardelli returns to the hypothesis that an ocean covered part of Mars’ northern hemisphere: a possible circumpolar ocean nicknamed Oceanus Borealis, which formed the present-day Red Planet about 3.2 billion years ago made a planet in the blue part. The scientist brings solid arguments to this debate, which began in the early 1970s.
Article by Xavier DemeersmanXavier Demeersman, published on February 22, 2014
No one doubts that there is water on Mars today (water ice is mostly found at the poles and underground). As evidence mounts, the hypothesis that rivers once flowed on its surface and filled lakes and seas is no longer a pipe dream. After all, that Mars was once covered by a vast ocean is an idea that researchers have been toying with for about four decades. Especially since the observation campaign of the Viking spacecraft, an ambitious mission to explore the Red Planet at the turn of the 1970s and 1980s, many have actually suggested that certain areas near the North Pole were once seashores. The heated debate triggered by these proposals was very controversial and has not yet been resolved due to a lack of conclusive evidence.
Far from being closed, the case is being reopened by a recent study by Lorena Moscardelli (University of Texas at Austin) published in the American Geological Society’s journal, GSA Today. The geologist provides new arguments that support the hypothesis of the previous existence of a large body of water that would have filled most of the plains of the northern hemisphere of Mars. A vast ocean nicknamed Oceanus Borealis that would have colored about a third of the surface of the solar system’s fourth planet (in an orbit at the edge of the habitable zone) blue about 3.2 billion years ago (late 2016), the Hesperian, beginning of the Amazon ).
Mars geological features found on Earth
For her study, the scientist examined detailed images from the Mars Reconnaissance Orbiter’s HiRise camera, in which we can see several rock-lined sections of the northern Martian hemisphere. To explain their distribution and location in space, she suggests that ancient underwater landslides on Mars worked to move them, similar to what happened and continues to happen at the bottom of Earth’s oceans. “We know that underwater landslides can carry large rocks – the size of houses – hundreds of kilometers into the deep waters of Earth’s oceans,” she recalls, naming several locations. well-known analogues such as those in southern Arkansas, the Santos Basin of Brazil or the Guandacol Formation in the Pangazo Basin of Argentina. Not to mention the one that affected thousands of square kilometers of land beneath the surface of Russia’s Barents Sea a million years ago.
Lorena Moscardelli questions those who defend the idea that the scattering of these rocks is the product of meteorite or asteroid impacts. “How then can we explain these rock fields that extend over hundreds of square kilometers without any impact craters in the area? » For them, “the underwater hypothesis represents a possible alternative”. However, how can we explain that the two coastlines highlighted by VikingViking near the North Pole vary so much in elevation, according to the latest data collected? Due to a possible oscillation of Mars’ rotation axis, suspects the geologist, who recalls research on the subject published in Nature in 2007.
What is attractive is that his hypothesis supporting the existence of an ocean in Mars’ past does not lack valid arguments. However, the geologist prefers to remain cautious and modest. “We need to learn more and more before we can be sure what might be true or false. » With regard to the seismic probes that are widely used in the search for gas and oil in the sea, Lorena Moscardelli regrets that there is too little exchange with her colleagues in the industry.