Cosmic cataclysm made Mars asymmetrical: study

As one hypothesis has it, shortly after Mars was formed, a cosmic object boasting a diameter of around 2,000 km impacted the planet. Photo: NASA

The northern hemisphere of Mars is located five to 10 kilometres lower than the Red Planet’s southern hemisphere, a study by a multi-national team of scientists, including a Polish researcher, has shown pointing to a disaster of a cosmic scale as the main culprit behind the asymmetry.

The research conducted by Dr Joanna Gurgurewicz and Dr. Daniel Mège of the Polish Academy of Sciences’ (PAN) Space Research Centre (CBK), Prof. Frédéric Schmidt of the Université Paris-Saclay, Dr. Sylvain Douté of the Université Grenoble Alpes, and Dr. Benoit Langlais of the Université Nantes Angers Le Mans offers a fascinating insight into Martian history and suggests that life could once be present on the Red Planet’s surface.

As one hypothesis has it, shortly after Mars was formed, a cosmic object with a diameter of around 2,000 km impacted the planet. This collision nearly wiped out the Red Planet from the face of the galaxy.

The diameter of the celestial body that collided at a speed of 21,000-36,000 km/h with the northern hemisphere of Mars at an angle of 30-60 degrees 4.5 billion years ago exceeded that of Pluto’s moon Charon, as the research team’s article published in Nature’s “Communications Earth & Environment” section shows. The planet survived the encounter, although it was left with a gigantic impact basin known today as Borealis.

“We began our research by means of serendipity while analysing super-high resolution photos of two deepest areas of the Valles Marineris large martian canyon. These photos had never been interpreted before. We have supplied them with 1 m-accuracy topographic models,” Dr. Daniel Mège, a member of the Polish Academy of Sciences (PAN) research team told Nature.

Peering into Mars

The photos were taken by the HiRISE telescope mounted on the NASA Mars Reconnaissance Orbiter. While analysing the photographs, scientists noticed a complex system of deformations. Such changes are a result of high temperatures and, by extension, can manifest at a depth of at least a couple of kilometres. On Earth, similar structures were observed on collision sites of former tectonic plates in Canada, Australia and Finland.

Since there is no tectonic activity on Mars, the deformations could not be seen on the surface. However, thanks to its depth, which reaches up to 10 km, the Valles Marineris canyon allows researchers to peer into Mars’ crust.

Researchers say that the long, mysterious crustal bundles north of Valles Marineris could be caused by the so-called reactivation of a shear zone.remely old mountain ranges in the vicinity of Valles Marineris, at the Ophir plateau, which stretch out parallelly to the border of the Borealis Basin, could be identified as rings originating from a cosmic impact.

Other proof of the collision is a long belt of tectonic breccia, with some blocks being 100 m tall. Only a powerful impact of meteorites could release the energy necessary to crush the rocks. As the authors of the paper posit, the plutonic formations could be very old as the lava covering the area cooled down 3.4 bn years ago.

The seismometer on the InSight mission picked up an earthquake in the shear zone on September 25, 2021. This could suggest that the Martian crust on the brim of the Borealis Basin could still be active. To determine the constitution of the rocks, the scientists used data from the CRISM spectrometer of the Mars Reconnaissance Orbiter, as well as a new method of nonlinear spectral unmixing of the spectra of minerals. Analyses carried out using this method identified the rock as a dark gabbro-type magmatic rock, inside of which hydrothermal liquids circulated.

Subject to pressure and temperature, gas and liquid substances moved through the cracks of the rock, causing interesting mineralisation, mainly in the form of sulphates. This type of mineralisation in the presence of the discovered deformations could imply metal deposits, including rare metals, Dr. Joann Gurgurewicz of the PAN’s Space Research Centre (CBK) said.

Life out there?

At the time when Mars was at the formation stage some 4.5 bn years ago, there was plenty of water under its crest. However, releasing hydrothermal circulation was unavoidable under the influence of heat, the researchers claimed.

This, in turn, led the team to suggest that “radiogenic heating might have contributed to maintaining a high geothermal gradient for some time, making the northern Valles Marineris a preferential region to investigate early life in situ.”

This offers a conclusion that the hydrothermal systems resulting from the Borealis impact could have allowed for the germination and maintenance of organic particles in favourable conditions. The said conditions were different from those reigning over other parts of the otherwise barren and inhabitable planet, where organic particles could not survive being wiped out by fluctuations in temperature, humidity, and standing no chance against wind, and solar, as well as galactic, radiation.

To read the whole paper, click here.