The history of Mars' dynamo as revealed by modeling magnetic anomalies near Tyrrhenus Mons and Syrtis Major

Abstract

The lack of magnetic anomalies within the major impact basins (Hellas, Argyre, and Isidis) has led many investigators to the conclusion that Mars' dynamo shut down prior to the time when these basins formed (∼4.0 Ga). We test this hypothesis by analyzing gravity and magnetic anomalies in the regions surrounding Tyrrhenus Mons and Syrtis Major, two volcanoes that were active during the late Noachian and Hesperian. We model magnetic anomalies that are associated with gravity anomalies and generally find that sources located below Noachian surface units tend to favor paleopoles near the equator and sources located below Hesperian surface features favor paleopoles near the geographical poles, suggesting polar wander during the Noachian‐Hesperian. Both paleopole clusters have positive and negative polarities, indicating reversals of the field during the Noachian and Hesperian. Magnetization of sources below Hesperian surfaces is evidence that the dynamo persisted beyond the formation of the major impact basins. The demagnetization associated with the volcanic construct of Syrtis Major implies dynamo cessation occurred while it was geologically active approximately 3.6 billion years ago. Timing of dynamo activity is fundamentally linked to Mars' climate via the stability of its atmosphere, and is coupled to the extent and duration of surface geologic activity. Thus, the dynamo history is key for understanding both when Mars was most geologically active and when it may have been most hospitable to life.

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

“…Strong crustal magnetic field measured by Mars Global Surveyor is suggestive of a core dynamo that ceased at some time during the Noachian (Acuña et al 2001;Langlais and Purucker 2007;Lillis et al 2008;Milbury et al 2012). Localized mantle heating may have affected the efficiency of the dynamo generation on Mars.…”

Methane storage capacity of the early martian cryosphere

“…However, analysis of gravity and magnetic anomalies around smaller craters and volcanoes show the presence of sources below younger surfaces, indicating that the dynamo was possibly active during the late Noachian. Studies on smaller structures seem to indicate that the cessation of the dynamo occurred after the formation of Apollinaris Patera and Antoniadi crater, but before Syrtis Major and Biblis Patera were fully built and Lowell was formed, narrowing the occurrence of dynamo cessation to between 3.79 Gyr and 3.75 Gyr (Langlais and Purucker, 2007;Langlais et al, 2012;Milbury et al, 2012). The timing of dynamo activity is somewhat linked to Mars' climate via the stability of its atmosphere, and is coupled to the extent and duration of surface geologic activity.…”

Planetary Magnetism

“…The paleopoles are found at low latitudes to midlatitudes and are suggestive of polar wander and polarity reversal (Milbury and Schubert, 2010). Coexistence of nearequatorial and near-polar paleopoles can be reconciled with the expectation of a moderate angular separation of dipole (magnetic) and rotational axes if one invokes significant polar wander during the active dynamo era (e.g., Boutin and Arkani-Hamed, 2006;Milbury et al, 2012;Sprenke, 2005).…”

“…A large number of putative paleopoles have been proposed but as yet no consensus has emerged (for a recent compilation, see Milbury et al, 2012). A general consideration of nonuniqueness in the interpretation of potential fields would suggest that without additional constraints, the problem remains intractable .…”