Mars’s two distinct hemispheres caused by mantle convection not giant impacts, study claims

Phys.org

Mars has northern and southern hemispheres like Earth, but their defining characteristics are markedly different, a phenomenon known as Martian dichotomy.
Much like on Earth, this seismic activity can be used to explore driving mechanisms beneath Mars’s surface.
To investigate this, Professors Sun and Tkalčić used low-frequency marsquake data recorded during NASA’s InSight mission that took place between 2018 and 2022, which aimed to study Mars’s crust, mantle and core.
Therefore, they conclude that the southern mantle experiences higher temperatures and lower viscosity.
Overall, Professors Sun and Tkalčić determine that mantle convection is the primary cause of Mars’s unusual dichotomy, not giant impacts as the alternative hypothesis suggests.

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The Martian dichotomy is the distinct difference between the northern and southern hemispheres of Mars, which are similar to those of Earth. Compared to the Northern Lowlands, the Southern Highlands are older, higher in altitude, and more cratered. Different wind patterns and localized weather phenomena are caused by the former’s elevated terrain, which naturally blocks airflow.

Large-scale convective movements of the mantle due to variations in its temperature and density, as well as giant impactors from space (~2,000 kilometers in diameter), are the main explanations for the origin of this dichotomy.

In an effort to better understand this origin story, research on Martian earthquakes, or marsquakes, has been published in Geophysical Research Letters. The driving mechanisms beneath Mars’ surface can be investigated using this seismic activity, just like on Earth.

“Earth and Mars, which are both in our solar system’s habitable zone, are frequently referred to as sister planets because they formed at roughly the same time (4:5 billion years ago). According to Professor Sun of the Chinese Academy of Sciences’ Institute of Geology and Geophysics, “Why does Earth seem so quiet and lifeless right now, while Mars is teeming with life?”.

We think that the two planets’ disparate internal processes and structures are what cause their contrast. Given that the dichotomy is among the most noticeable aspects of Mars’ internal structures and surface elevation, we intend to investigate its causes in order to try to answer a riddle that has baffled scientists for half a century. “,”.

Professor Tkalčić of The Australian National University goes on to explain the importance of the project by saying, “Even though the image of the Earth’s deep interior is becoming less hazy, we still don’t understand the interiors of other terrestrial planets.”. Utilizing the waves from earthquakes captured by the InSight seismometer, we investigated the interior of Mars in this study in a manner similar to that of earthquakes on Earth.

“Knowing our planetary neighbor will enable us to investigate the Earth’s past, present, and future. Conversely, knowing the Earth is necessary to comprehend the solar system. “.

Professors Sun and Tkalčić used low-frequency marsquake data from NASA’s InSight mission, which observed Mars’ crust, mantle, and core between 2018 and 2022, to look into this.

Because Mars only has “one seismometer that recorded marsquakes and impacts for a limited time window, while on Earth we have thousands of seismometers that continuously record the ground motion,” it was a little difficult to get the required data. “,”.

According to Professor Sun, “Mars has substantially less tectonic activity than Earth, which leads to fewer and typically lower-magnitude earthquakes.”. Additionally, despite protective shielding, the seismometer’s surface location exposes it to diurnal winds, which result in a noticeably low signal-to-noise ratio. “..”.

The researchers used cutting-edge techniques to improve the signal-to-noise ratio. Based on how seismic waves travel from these marsquakes to the InSight seismometer, they compared the new cluster of six marsquakes in the Southern Highlands’ Terra Cimmeria region to 16 previously known marsquakes from Cerberus Fossae in the Northern Lowlands.

Each set’s quality factor, a physical indicator of how much a seismic wave weakens as it passes through Mars’ surface and interior, was then calculated by the scientists. The researchers discovered a pattern of southern-northern seismic attenuation because Terra Cimmeria had a lower quality factor than Cerberus Fossae, which indicates more seismic wave weakening.

They therefore draw the conclusion that the southern mantle has lower viscosity and higher temperatures. This is further supported by the fact that the thicker crust of the southern hemisphere slows down heat loss from the interior, increasing its fluidity and causing more vigorous convection.

As Professor Sun points out, “Experimental data correlating seismic quality factor with temperature suggests that the mantle beneath the Southern Highlands could reach temperatures of approximately 1,000°C, compared to around 800°C or slightly higher beneath the Northern Lowlands.”.

Overall, Professors Sun and Tkalčić conclude that, contrary to the alternative hypothesis, giant impacts are not the main cause of Mars’ unusual dichotomy, but rather mantle convection.

But as Professor Sun outlines the next two-pronged strategy for comprehending the notable distinctions between modern-day Mars and Earth, their research goes on.

“First, as we continue to examine the internal structure of Mars in relation to Earth, we estimate that the crust at the InSight landing site is about 50 kilometers thick, which is significantly thicker than the average continental crust (about 35 kilometers) and oceanic crust (about 10 kilometers or less) on Earth. We will thus investigate why Mars has such a thicker crust even though it is almost half as large as Earth.

“Secondly, we will search Mars for liquid water. Water is known to be necessary for life to exist. There is evidence that Mars once had enormous oceans, but it’s possible that a large portion of its liquid water either escaped into space or was trapped in the crust. Our goal is to use seismological methods to investigate whether liquid water still exists in the Martian crust.

Examining these two characteristics might provide insights into the different evolutionary trajectories of Earth and Mars as well as hints about the possible future and ultimate destiny of our own planet. “..”.

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