Locked beneath a single-plate crust, Mars’ mantle holds a frozen record of the red planet’s primordial past, according to a new study of Martian seismic data collected by NASA’s InSight mission. The findings reveal a highly heterogenous and disordered mantle, born from ancient impacts and chaotic convection in the planet’s early 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.” 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, Mars’ 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 and colleagues studied the seismic signatures of marsquakes to better constrain the nature of Mars’ mantle. By analyzing eight well-recorded quakes, including those triggered by meteorite impacts, Charalambous et al. discovered that high-frequency P-wave arrivals were systematically delayed as they traversed the deeper portions of the mantle. According to the authors, these delays reveal subtle, kilometer-scale compositional variations within 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. The scaling of Mars’ mantle heterogeneity suggests an origin in highly energetic and disruptive processes, including massive impacts early in the planet’s history, which fractured the planet’s interior, mixing both foreign and crustal materials 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, these features became frozen in place as Mars’ crust cooled and mantle convection stalled.
