What We Can Learn About Mars From The Magnetism of Returned Samples

The Red Planet is a magnetic planet. The Martian crust contains strong magnetization from a core dynamo that likely was active during the Noachian period when the surface may have been habitable. The evolution of the dynamo may have played a central role in the evolution of the early atmosphere and the planet’s transition to the current cold and dry state.

However, the nature and history of the dynamo and crustal magnetization are poorly understood given the lack of well-preserved, oriented, ancient samples with geologic context available for laboratory study.

Here, we describe how magnetic measurements of returned samples could transform our understanding of six key unknowns about Mars’ planetary evolution and habitability. Such measurements could i) determine the history of the Martian dynamo field’s intensity; ii) determine the history of the Martian dynamo field’s direction; iii) test the hypothesis that Mars experienced plate tectonics or true polar wander; iv) constrain the thermal and aqueous alteration history of the samples; v) identify sources of Martian crustal magnetization and vi) characterize sedimentary and magmatic processes on Mars.

We discuss how these goals can be achieved using future laboratory analyses of samples acquired by the Perseverance rover.

Although Mars does not have an internally generated magnetic field today, the presence of strong magnetization in the Martian crust and in some Martian meteorites demonstrates that there was once a global magnetic field on Mars (1). This field was likely generated by the dynamo process, in which the mechanical energy of an advecting, conductive fluid in the planet’s metallic interior inductively drives electrical currents that generate a large-scale field. The intensity, geometry, and lifetime of the dynamo field are poorly known but have major implications for the thermal and climatic evolution of Mars and the possibility that it was habitable.

There are two key reasons we know so little about the history of Martian magnetism. First, our magnetic records from in situ on Mars are mainly limited to orbital measurements of the present-day remanent magnetic field of the crust. Second, laboratory studies of Martian rocks are limited to meteorites, most of which likely postdate the end of the dynamo and all of which both lack geologic context and are unoriented relative to Martian geographic coordinates.

The Mars sample return campaign (MSR) aims to fundamentally change this by returning up to ~30 absolutely oriented samples (2), mostly from bedrock and that include materials likely formed while there was a dynamo. Here, we discuss how paleomagnetic and rock magnetic studies of returned samples from Mars could transform our understanding of Martian geology and astrobiology by addressing at least six key science objectives (Fig. 1):

Schematic showing six Mars magnetism science objectives. 1. Determine the history of the Martian dynamo field’s intensity. 2. Determine the history of the Martian dynamo field’s direction. 3. Test the hypothesis that Mars experienced plate tectonics or true polar wander. 4. Constrain the thermal and aqueous alteration history of the samples. 5. Identify sources of Martian crustal magnetization. 6. Characterize sedimentary and magmatic processes on Mars. — PNAS via PubMed

What We Can Learn About Mars From The Magnetism of Returned Samples, PNAS via PubMed (open access)

Astrobiology