Mercury’s magnetopause (in red) and magnetic field lines (in blue) modeled from Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) observations. This still is taken from a video showing offset magnetic field. Credit: JHU/APL
Source: Journal of Geophysical Research: Space Physics

What’s old is new again on Mercury—at least when it comes to simulations of the planet’s magnetic field.

Like Earth, Mercury has a global magnetic field generated from within the planet that shields it from the Sun’s most powerful rays and particles. It deflects them around the planet to form a roughly teardrop shape, with a round, blunted end facing the Sun and a tail facing away. This boundary of protection is called the magnetopause.

However, scientists have gone back and forth on how to model Mercury’s magnetic field and the resulting magnetopause. Any complete model must generate a realistically shaped magnetopause, but this is not as easy as it seems: In addition to the main source of Mercury’s magnetic field—its internal dynamo, driven by the convection of molten material at its core—the forces of electricity and magnetism generate electrical currents that flow along the magnetopause and across the magnetic tail, which in turn affect the shape of the magnetopause itself in a feedback loop of sorts.

For decades, the only data from Mercury that scientists had to develop their models came from two flybys through Mercury’s magnetic cavity by NASA’s Mariner 10 probe in the mid-1970s. The first models of Mercury’s magnetic field were either extremely simplified or scaled-down versions of models of Earth.

However, observations from NASA’s Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft, which reached the scorching-hot planet in 2011, quickly showed that Mercury is not like Earth. Using MESSENGER data of limited spatial distribution, scientists initially modeled the magnetosphere in the form of a simple paraboloid, like an inside-out satellite antenna dish. However, this model didn’t quite fit the data.

Continuous monitoring of the magnetic field during the 4-year mission allowed for a more accurate representation of the magnetic field. The new model by Korth et al. brings the Earth-like shape back into vogue. Compared with observed crossings of the magnetopause by MESSENGER, the team finds that the new model results in a significant improvement over the paraboloid version.

However, there are still places where the data don’t quite line up with either model—especially on the side of the magnetopause facing the Sun. The authors say that this means there are still unknown factors affecting the magnetic field. One cause for optimism, however, is that their new model can more easily incorporate additional sources of magnetism, and the residuals should aid scientists in finding out what they are. (Journal of Geophysical Research: Space Physics, doi:10.1002/2015JA021022, 2015)

—Mark Zastrow, Freelance Writer

Citation: Zastrow, M. (2015), Mercury’s magnetosphere model gets retro makeover, Eos, 96, doi:10.1029/2015EO040579. Published on 3 December 2015.

Text © 2015. The authors. CC BY-NC 3.0
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