Solar Wind effects on Mars’ nightside magnetic field revealed

by Simon Mansfield

Sydney, Australia (SPX) Sep 20, 2024

A new study led by Postdoctoral Researcher Jiawei Gao from the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS), reveals how Mars’ magnetic field responds to the influence of solar winds. Unlike Earth, Mars lacks a global dipolar magnetic field but possesses localized crustal magnetic fields. The planet’s interaction with the Interplanetary Magnetic Field (IMF) carried by the solar wind and its highly conductive ionosphere creates an induced magnetosphere, a feature that plays a key role in atmospheric loss and Mars’ climatic evolution.

Published in ‘Earth and Planetary Physics’, this research explores how variations in upstream solar wind conditions affect the low-altitude magnetic field on Mars. Changes in solar wind dynamic pressure, IMF strength and direction, and solar extreme ultraviolet (EUV) flux, which shift with solar seasons, have a direct impact on the magnetic field’s topology. Historical solar winds were denser and faster, meaning past conditions on Mars may have experienced more frequent intense pressure events similar to those caused by modern-day coronal mass ejections (CMEs) and co-rotating interaction regions (CIRs).

During periods of higher solar activity in the past, the draped magnetic field may have penetrated deeper into Mars’ ionosphere, potentially resulting in higher rates of atmospheric ion escape. As a result, the planet’s magnetic response to the IMF is considered crucial for understanding how solar activity influenced Mars’ atmospheric history and escape rates.

Gao’s team analyzed MAVEN spacecraft data from November 2014 to May 2023, examining magnetic field residuals in Mars’ nightside ionosphere. Four solar wind drivers were considered: IMF intensity, solar wind dynamic pressure, EUV flux, and Martian seasons. The study identified that the magnetic field residuals show a strong correlation with both the IMF’s intensity and the dynamic pressure of the solar wind. In contrast, the correlation with EUV flux and Martian seasons was weak. The study found that the IMF can reach altitudes of 100-200 km in Mars’ ionosphere when IMF intensity and solar wind dynamic pressure are elevated.

“Our research not only advances our knowledge of Mars’ present magnetic environment but also opens a window into its atmospheric past. By understanding how Mars’ atmosphere responded to a more active early Sun, we can better conjecture the planet’s capacity to have supported life, enriching our quest for uncovering Mars’ ancient secrets,” said Dr. Gao.

Research Report:Influence of upstream solar wind on magnetic field distribution in the Martian nightside ionosphere

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