Gravity and Magnetic Field Signatures in Hydrothermally Affected Regions on Mars

Multiple lines of evidence indicate that liquid water-rock interactions occurred on ancient Mars, particularly within the crust, where hydrothermal systems have been hypothesized. Such hydrothermal circulation (HC) can significantly lower temperatures in the crust, thereby restricting the viscoelastic relaxation of impact craters. Craters with minimal relaxation are characterized by their large depth-to-diameter ratio and prominent Bouguer gravity anomalies. Additionally, HC can induce magnetic anomalies through chemical remanent magnetization (CRM). Consequently, if HC was widespread on Mars, the gravitational signatures of unrelaxed craters may correlate with their magnetic signatures. To investigate how HC influenced the magnetic characteristics of the Martian crust, we focus on the region surrounding several unrelaxed craters in the southern highlands, where hydrothermal activity was likely prevalent. We use a newly developed joint inversion approach and model magnetization and density in such regions to investigate how hydrothermal systems affect those parameters. The inversion approach makes use of a mutual information term in which models with a parameter relationship are favored, that is, models in which magnetization and density distributions are correlated. Despite showing large Bouguer gravity anomalies and forming over 3.75 billion years ago, when the Martian dynamo was most likely active, investigated craters and surrounding regions exhibit minimal magnetic anomalies. We propose that this lack of magnetic signatures is most likely due to demagnetization of the crust through CRM, induced by HC long after the Martian dynamo ceased. Our findings suggest that deep, long-lived hydrothermal systems—likely fueled by heat-producing elements—were present, potentially creating habitable conditions on early Mars.