Scientists working on NASA’s Mercury orbiter, the Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft, have watched in recent years as coronal mass ejections from the Sun sent solar winds sailing toward the solar system’s innermost planet during the recent peaks of the solar cycle. The team studied what the most extreme of these events do to the planet’s magnetosphere—the region controlled by Mercury’s weak magnetic field.
Since the spacecraft arrived in 2011, its observations have shown that Mercury’s magnetic field closely aligns with the planet’s rotation axis and carries a polarity similar to Earth’s. The tiny planet packs a large iron core; however, its magnetic field reaches just one fifth of its radius beyond the surface and packs about 1% of the strength of Earth’s.
Slavin et al. examined the solar wind’s impact on reconnection, where magnetic field lines from the Sun connect with field lines at a planet, releasing both kinetic and thermal energy and accelerating particles to high speeds. The team identified three spacecraft passes where the planet’s magnetic field exceeded 300 nanoteslas—roughly 3 times the strength typically seen. To hit those levels, the authors say that the pressure of solar wind hitting Mercury must have risen by some 4 to 9 times above normal in each instance.
The team’s results show that Mercury’s magnetic reconnection is intense and that the magnetopause actually intersected the planet’s surface at times in the southern hemisphere, where the magnetic field is weakest. The authors say their analysis shows that the edge of Mercury’s magnetic field responds to increasing solar wind pressure very similarly to how Earth responds. (Journal of Geophysical Research: Space Physics, doi:10.1002/2014JA020319, 2014)
—Eric Betz, Freelance Writer
Citation: Betz, E. (2015), Scientists watch solar winds blast Mercury’s magnetic field, Eos, 96, doi:10.1029/2015EO026607. Published on 25 March 2015.