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

This study is led by Postdoctoral researcher Jiawei Gao from IGGCAS. Unlike Earth, Mars lacks a global dipolar magnetic field; the planet does have locally distributed crustal magnetic fields. Mars is exposed to the solar wind, which carries the Interplanetary Magnetic Field (IMF) that interacts with Mars’ highly conductive ionosphere, resulting in an induced magnetosphere. This study, recently featured on the front cover of Earth and Planetary Physics, reveals how the Red Planet's magnetic field responds to solar winds, providing key insights into atmospheric escape processes and Mars' climatic evolution.

An intriguing aspect of this emerging scenario is the question: How do variations in upstream solar wind conditions impact the topology of the low-altitude induced magnetic field on Mars? The induced field topology exhibits statistical variation in response to solar conditions, such as the IMF’s strength and direction, solar wind dynamic pressure, and solar extreme ultraviolet (EUV) flux, which vary with solar seasons. Given that the historical solar wind is believed to have been denser and faster than today’s conditions, normal solar wind conditions in the past may have resembled today’s extreme dynamic pressure events, such as those during coronal mass ejections (CMEs) and in co-rotating interaction regions (CIRs).

Depending on the solar conditions experienced by Mars in the past, the draped magnetic field may have routinely penetrated deep into the ionosphere, potentially leading to significantly higher rates of ionospheric escape to space for early Mars compared to the present day. Therefore, understanding how solar conditions influence the Martian ionospheric magnetic field, especially the penetration depth of the IMF, is crucial for elucidating the past history of Mars’s ion escape processes.

Using MAVEN data from November 2014 to May 2023, this research have investigated the distribution of magnetic field residuals in the Martian nightside ionosphere under four upstream solar wind drivers: the intensity of the IMF, solar wind dynamic pressure, solar extreme ultraviolet (EUV) flux, and Martian seasons. The key finding is: The magnetic field residuals in the Martian ionosphere show significant positive correlation with the intensity of the IMF and solar wind dynamic pressure; they are weakly correlated with EUV flux and Martian seasons. Specifically, the IMF can reach the 100−200 km altitude range under high and medium the intensity of the IMF and solar wind dynamic pressure.

"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." Dr. Gao says.

See the article:

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

http://doi.org/10.26464/epp2024052