Weak magnetism of Martian impact basins may reflect cooling in a reversing dynamo

• Published in: Nature communications 2024-08, Vol.15 (1), p.6831-16, Article 6831
• Main Authors: Steele, S. C., Fu, R. R., Mittelholz, A., Ermakov, A. I., Citron, R. I., Lillis, R. J.
• Format: Article
• Language: English
• Subjects: 704/2151/214; 704/445; 704/445/845; Basins; Earth mantle; Humanities and Social Sciences; Magnetic fields; Magnetic properties; Magnetic reversals; Magnetism; Mars; Mars atmosphere; Mars surface; Mars volcanoes; Meteors & meteorites; multidisciplinary; Planetary geology; Planetary magnetic fields; Planetary mantles; Science; Science (multidisciplinary); SNC meteorites; Spacecraft
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-51092-4

Understanding the longevity of Mars’s dynamo is key to interpreting the planet’s atmospheric loss history and the properties of its deep interior. Satellite data showing magnetic lows above many large impact basins formed 4.1-3.7 billion years ago (Ga) have been interpreted as evidence that Mars’s dynamo terminated before 4.1 Ga—at least 0.4 Gy before intense late Noachian/early Hesperian hydrological activity. However, evidence for a longer-lived, reversing dynamo from young volcanics and the Martian meteorite ALH 84001 supports an alternative interpretation of Mars’s apparently demagnetized basins. To understand how a reversing dynamo would affect basin fields, here we model the cooling and magnetization of 200-2200 km diameter impact basins under a range of Earth-like reversal frequencies. We find that magnetic reversals efficiently reduce field strengths above large basins. In particular, if the magnetic properties of the Martian mantle are similar to most Martian meteorites and late remagnetization of the near surface is widespread, >90% of large ( > 800 km diameter) basins would appear demagnetized at spacecraft altitudes. This ultimately implies that Mars’s apparently demagnetized basins do not require an early dynamo cessation. A long-lived and reversing dynamo, unlike alternative scenarios, satisfies all available constraints on Mars’s magnetic history. Weak magnetic fields above Mars’s large impact basins are often interpreted as a signature of the dynamo’s early cessation. Here, the authors demonstrate that these weakly magnetic basins may instead have formed in a long-lived but reversing dynamo.