The study addresses the long-standing mystery of the Martian dichotomy, where the southern hemisphere's crust is significantly thicker and lies five to six kilometers higher than the northern hemisphere. This disparity covers nearly two-thirds of Mars' surface.
According to the researchers, the dichotomy likely resulted from convection-the transfer of heat within the Martian mantle-over hundreds of millions to billions of years. The mantle, situated between Mars' crust and core, plays a critical role in the planet's thermal and geological dynamics.
ANU geophysicist and co-author Professor Hrvoje Tkalcic described the hemispherical differences as "one of the biggest mysteries in the solar system." He explained: "We analysed waveform data from so-called low frequency marsquakes captured by NASA's InSight seismograph on Mars. In doing this, we located a cluster of six previously detected, but unlocated marsquakes in the planet's southern highlands, in the Terra Cimmeria region."
Co-author Professor Weijia Sun from the Chinese Academy of Sciences emphasized the scale of the dichotomy, comparing the elevation difference to Earth's tallest mountain ranges. The southern hemisphere, less studied than its northern counterpart, revealed key differences through marsquake data.
Professor Tkalcic noted, "The data from these marsquakes, when compared with the well-documented northern hemisphere marsquakes, reveal how the planet's southern hemisphere is significantly hotter compared to its northern hemisphere. Understanding whether convection is taking place offers clues into how Mars has evolved into its current state over billions of years."
Two main theories attempt to explain the dichotomy. The endogenic hypothesis suggests internal convection caused the differences, while the exogenic hypothesis attributes them to astronomical impacts. This study's findings strongly support the endogenic hypothesis, providing the first observational evidence for this theory.
"On Earth, we have thousands of seismic stations scattered around the planet. But on Mars, we have a single station, so the challenge is determining the location of these marsquakes when you have only a single instrument," Professor Tkalcic explained.
NASA's InSight lander, operational from 2018 to 2022, collected data on marsquakes, Martian weather, and the planet's internal structure. Researchers suggest it could serve as a prototype for future planetary missions. Professor Sun added, "Deciphering the formation of this dichotomy could also have some implications for the paleoclimate changes on Mars."
Research Report:Constraints on the Origin of the Martian Dichotomy From Southern Highlands Marsquakes
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