Key Takeaways:
- Mars' single-plate surface, unlike Earth's active plate tectonics, allows for preservation of its mantle's early internal history, providing insights into rocky planet formation and evolution.
- Analysis of seismic data from the InSight lander revealed delays in high-frequency P-wave arrivals in Mars' deeper mantle, indicating subtle variations in its composition.
- These variations, on the order of a kilometer, are interpreted as remnants of early Martian history, including massive impacts and magma ocean crystallization, preserved due to the lack of plate tectonics.
- The study suggests that the preserved heterogeneity in Mars' mantle offers a unique opportunity to understand the geological history and thermochemical evolution of a planet under a stagnant lid, a common tectonic regime in the solar system, with implications for habitability.
A planet’s mantle — the vast layer that lies sandwiched between its crust and core — preserves crucial evidence about planetary origin and evolution. Unlike Earth, where active plate tectonics continually stirs the mantle, Mars is a smaller planet with a single-plate surface. As such, its mantle undergoes far less mixing, meaning it may preserve a record of the planet’s early internal history, which could offer valuable insights into how rocky worlds form and evolve.
Using data from NASA’s InSight lander, Constantinos Charalambous from the Imperial College of London and colleagues studied the seismic signatures of marsquakes to better understand the nature of Mars’ mantle. By analyzing eight well-recorded quakes, including those triggered by meteorite impacts, the team discovered that high-frequency P-wave arrivals were delayed as they traveled through the deeper portions of the mantle. P-waves, or Primary waves, are the fastest seismic waves. They travel through material much like sound waves. According to the authors, the delays reveal subtle, variations — about a kilometer (0.62 mile) across — in the make-up of the planet’s mantle. Because Mars lacks plate tectonics and large-scale recycling, these small-scale irregularities must instead be remnants of its earliest history.
“Whereas Earth’s early geological records remain elusive, the identification of preserved ancient mantle heterogeneity on Mars offers an unprecedented window into the geological history and thermochemical evolution of a terrestrial planet under a stagnant lid, the prevalent tectonic regime in our solar system,” write the authors. “This evolution holds key implications for understanding the preconditions for habitability of rocky bodies across our solar system and beyond.”
The scaling of Mars’ mantle’s diversity suggests that it came about as a result of highly energetic and disruptive processes. They include massive impacts early in Mars’ history, which fractured the planet’s interior, mixing material from the crust and from space into the mantle at a planetary scale. Moreover, the crystallization of vast magma oceans generated in the aftermath likely introduced additional variations. Instead of being erased by plate tectonics and other forces, these features became frozen in place as Mars’ crust cooled and mantle convection stalled.
