How Mars’s Magnetic Field Let Its Atmosphere Slip Away

hubie writes:

One of the primary drivers for the distinct lack of a Martian atmosphere is believed to be the loss of atmospheric molecules that are stripped away by the passing solar wind. A strong planetary magnetic field would divert the solar wind around the planet and protect the Martian atmosphere. The MAVEN spacecraft confirmed this is happening, and some interesting ideas have been floated to mitigate the effect.

A recent paper published in JGR: Space Physics used Magnetohydrodynamic (MHD) models to investigate the magnitude of the effect on atmospheric retention that a magnetic field would have on Mars and found a very interesting result. Their models confirmed that the rate of atmospheric loss was six times higher for a planet with no magnetic field compared to a planet with a strong magnetic field; however, they found the highest rate of atmospheric loss was actually when there was a weak magnetic field.

But the highest rate of atmospheric ion loss was with a weak magnetic field-6 times faster than with no magnetic field at all. The team found the reason was the magnetic field lines, which guide the motion of charged particles, were easily blown back by the solar wind, creating a path for these ions to escape into space above Mars's nightside. This means that instead of providing a small measure of protection, Mars's remnant magnetic field could actually have sped the planet's transformation into the cold, barren world it is today.

Research Paper: Sakata, et al., Effects of an Intrinsic Magnetic Field on Ion Loss From Ancient Mars Based on Multispecies MHD Simulations, Journal of Geophysical Research: Space Physics, https://doi.org/10.1029/2019JA026945, 2020

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