F
or many years, the prevailing notion was that Mars was geologically a "boring" planet. This is because unlike Earth, which features a dynamic network of constantly moving tectonic plates, Mars does not have any such tectonic plates. Due to this lack of moving plates, it was previously believed that Mars could not support any complex volcano formation and was thus classified as a "stagnant lid" planet, a planet with a non-moving outer surface that features only isolated volcanoes.
However, a new discovery has come along to challenge this view.
A team from the University of Oxford, working with the University of Bristol and the University of Oxford's Department of Statistics, has discovered that there existed an extensive system of volcanoes in Mars' history that bears an uncanny resemblance to that on Earth, even though Mars lacks any form of plate tectonics whatsoever.
The research team did not use any excavation on Mars or launch another probe. Rather, they reviewed data from NASA's Insight lander, which in 2018 put the first seismograph on the surface of Mars. For years, the spacecraft was silently monitoring the Red Planet, collecting information about "marsquakes"—marsquakes being Mars's equivalent of earthquakes—as well as information about vibrations from meteorite impacts.
By analyzing the path of the seismic waves that passed through the crust of Mars, the researchers came to an unexpected conclusion—there were signs of a layer of melt-depleted lower crust underlying an evolved upper layer. To put it simply, the evidence suggested the presence of a trace left by magma that did not erupt at once but continued moving, mixing, and evolving for a long period of time.
The phenomenon described above is called the "transcrustal magmatic system." It is an underground network where magma is stored, evolved, and interacts with other rocks throughout the crust. Previously, scientists believed that such systems could only develop due to plate tectonics since that is how they form on Earth.
However, on Mars, there are no moving tectonic plates. The surface of the planet has been relatively stationary for millions of years. This means that such a complicated and Earth-like magma plumbing system without tectonic activity pushes the researchers to reconsider the possibilities of planetary crust evolution.
As per the research paper, the scientists believe that on Mars, the complex structure formed with the help of a different mechanism: heavy internal recycling process. Magma coming up from very deep inside the planet has been recycled many times and formed an extremely complicated structure instead of a simple one, which one could expect on a "dead" planet without any tectonics.
At the same time, based on the estimates, this huge number of magmatic rocks does not form some small pocket. On the contrary, this system is probably spread all around Mars' northern hemisphere.
Dr. Tobermory Mackay-Champion, who headed the team conducting this research (based at Oxford University and now based at the University of Bristol), made the transition of thoughts clear:
"We have always assumed that the volcanoes on Mars are quite a bit simpler than those on Earth. However, our finding indicates that Mars can sustain complex systems of molten rocks that rework and evolve across its entire crust."
Professor Jon Wade of Oxford, a co-author of the research paper, further elaborated:
"One of the greatest issues of planetary science is the uniqueness of Earth. However, if Mars is able to form such a complex crust despite the absence of plate tectonics, maybe habitable environments can occur on other planets too."
This is a strong statement indeed. It is indicative of the fact that planets that were previously ruled out as "too small" or "geologically inert" to be capable of hosting complex chemical reactions and environments conducive to life may be reconsidered.
However, this is not an assertion that there was, or there still is, life on Mars. Nevertheless, it has an effect on the notion of habitability, which refers to the set of conditions a particular planet must have in order to be able to support life.
Plate tectonics is one of the key factors responsible for the nutrient recycling, climate regulation, and chemical diversity on the surface of our planet. It was thought that a planet had to have plate tectonics in order to acquire such a geologic diversity.
Should Mars have found a way to obtain something like that by means of a totally different mechanism—internal magma recycling, rather than plate tectonics—this would require the rewriting of the rules defining the planets that should be studied.
Of course, this observation is not unique. In recent years, a number of independent studies have undermined the assumption that Mars is geologically "dead":
The study of seismic activity has established the presence of a mantle plume—essentially, a large stream of hot rock rising up from deep below Mars' surface—located below the area called Elysium Planitia.
Studies using orbital imaging have revealed volcanic zones on Mars with a complicated history of multistage volcanic activity, rather than a single-stage volcanic activity.
It was suggested that at least some of Mars' most recent volcanic systems were fueled by underground lava chambers, which lasted much longer than a single burst of activity.
All these results collectively point to a planet that has been much more chemically and geologically active throughout its history, and maybe even now, than we previously assumed.
