2025-08-28 NASA
Scientists believe giant impacts — like the one depicted in this artist’s concept — occurred on Mars 4.5 billion years ago, injecting debris from the impact deep into the planet’s mantle. NASA’s InSight lander detected this debris before the mission’s end in 2022. NASA/JPL-Caltech
＜関連情報＞
- https://www.nasa.gov/missions/insight/nasa-marsquake-data-reveals-lumpy-nature-of-red-planets-interior/
- https://www.science.org/doi/10.1126/science.adk4292
- https://tiisys.com/blog/2025/02/04/post-160725/
火星マントルの高度な不均一性を示す地震学的証拠 Seismic evidence for a highly heterogeneous martian mantle
Constantinos Charalambous, W. Thomas Pike, Doyeon Kim, Henri Samuel, […] , and W. Bruce Banerdt
Science Published:28 Aug 2025
DOI:https://doi.org/10.1126/science.adk4292
Editor’s summary
Mars is a single-plate planet. In contrast to Earth, where subducting plates have churned the mantle for billions of years, the interior of Mars may preserve characteristics of its early evolution. Charalambous et al. detected marsquake waveforms arriving at NASA’s InSight lander and saw an apparent delay in the high-frequency arrivals that increased with travel distance through Mars’ mantle. They attribute these delays to very fine-scale heterogeneities, the result of chaotic mantle convection during Mars’ impact-filled early history. This widespread heterogeneity was then frozen in place as the planet’s crust cooled and mantle convection slowed to a creep. —Angela Hessler
Abstract
A planet’s interior is a time capsule, preserving clues to its early history. We report the discovery of kilometer-scale heterogeneities throughout Mars’ mantle, detected seismically through pronounced wavefront distortion of energy arriving from deeply probing marsquakes. These heterogeneities, likely remnants of the planet’s formation, imply a mantle that has undergone limited mixing driven by sluggish convection. Their size and survival constrain Mars’ poorly known mantle rheology, indicating a high viscosity of 1021.3 to 1021.9 pascal-seconds and low temperature dependence, with an effective activation energy of 70 to 90 kilojoules per mole, suggesting a mantle deforming by dislocation creep. The limited mixing, coupled with ubiquitous, scale-invariant heterogeneities, reflects a highly disordered mantle, characteristic of the more primitive interior evolution of a single-plate planet, contrasting sharply with the tectonically active Earth.
