The Northern and Southern Hemispheres of Mars differ greatly in their topography. The first one is predominantly lowland, while the second one is mountainous. As the researchers found out, the reason for this is magmatic activity inside the planet.

Martian dichotomy
Mars has Northern and Southern Hemispheres, like Earth, but their defining characteristics are markedly different. This phenomenon is known as the Martian dichotomy. The Southern Highlands are older, higher, and more cratered than the Northern Highlands. The elevated terrain serves as a natural barrier to air currents, resulting in a variety of wind patterns and contributing to localized weather events.
The explanation for the origin of this dichotomy is primarily related to giant impactors (~2000 km in diameter) from space and large-scale convective motions of the mantle caused by differences in its temperature and density.
A study published in the journal Geophysical Research Letters attempted to further unravel this origin story by studying Marsquakes. As on Earth, this seismic activity can be used to study the driving mechanisms beneath the surface of Mars.
Mars’ mysterious interior
“Earth and Mars are often considered sister planets and were formed in the same period (4.5 billion years ago), both located within the habitable zone of our solar system. Why is Earth teeming with life, while Mars appears so silent and devoid of life at present?” — asks Prof. Sun of the Institute of Geology and Geophysics, Chinese Academy of Sciences.
“We believe that the contrast between the two planets is due to differences in their internal structures and processes. Given that the dichotomy is one of the most striking features of the surface topography and internal structures on Mars, we hope to find an answer to this question by investigating the causes of the dichotomy and try to solve a mystery that has intrigued scientists for 50 years.”
“While the picture of Earth’s deep interior is becoming less blurred, we still don’t understand the internal structure of other planets,” Professor Tkalčić of the Australian National University explains the significance of the project. “In this study, we explored the interior of Mars using waves from Marsquakes recorded by the InSight seismometer, just as we do on Earth with earthquakes. Understanding the solar system depends on our knowledge of Earth, and vice versa: understanding our planetary neighbor will allow us to explore the planet’s past, present and future.”
Study of seismographic data
Professors Sun and Tkalčić used data from low-frequency Marsquakes recorded during NASA’s InSight mission, which took place between 2018 and 2022 and aimed to study the crust, mantle and core of Mars.
Obtaining the necessary data proved to be a slightly difficult task, given that Mars has a single seismometer that recorded quakes and tremors for a limited period of time, while on Earth we have thousands of seismometers continuously recording ground motion.
Mars shows much less tectonic activity than Earth, resulting in less and generally lower magnitude Marsquakes. In addition, the surface location of the seismometer exposes it to daytime winds, which, despite the protective shielding, contribute to a much lower signal-to-noise ratio.
By improving the signal-to-noise ratio using the most advanced methods, the researchers detected a new cluster of six quakes in the Terra Cimmeria region of the Southern Highlands and compared them to 16 previously known quakes from the Cerberus Fossae in the Northern Lowlands, based on how seismic waves travel from these quakes to the InSight seismometer.
The scientists subsequently determined a quality factor for each set, which is a physical measure of how much the seismic wave attenuates as it travels through the interior and surface of Mars. Because Terra Cimmeria has a lower quality factor (meaning more seismic wave attenuation) than Cerberus Fossae, the researchers determined the pattern of seismic wave attenuation from south to north.
Therefore, they conclude that the southern mantle has higher temperatures and lower viscosity. This is also supported by the fact that the thickness of the southern hemisphere crust slows the loss of heat from the interior, making it more fluid and consequently experiencing stronger convection.
Overall, Professors Sun and Tkalčić determine that mantle convection is the primary cause of Mars’ unusual dichotomy, not giant collisions as the alternative hypothesis suggests.
Scientific approach to the study of the Martian interior
But their research continues as Prof. Sun explains the following two-pronged approach to understanding the essential differences between modern Mars and Earth.
First, continuing our study of the internal structure of Mars compared to Earth, the crust at the InSight landing site is estimated to be about 50 km thick, significantly thicker than Earth’s average continental crust (about 35 km) and oceanic crust (about 10 km or less). Therefore, we will investigate why Mars, despite being almost half the size of Earth, has such a thick crust.
Second, we will be looking for liquid water on Mars. It is well known that water is necessary to sustain life. Evidence suggests that Mars once had vast oceans, but much of the liquid water may have evaporated into space or been sequestered in the Earth’s crust. To investigate this, we aim to apply seismological techniques to determine whether liquid water is preserved in the Martian crust. Studying these two features can help us understand the differences in the evolutionary paths of Mars and Earth, as well as provide clues about the potential future and ultimate fate of our planet.
According to phys.org