Mercury A to Z: X-Class Solar Flares

Hello, friends!  For this year’s A to Z Challenge, my theme is the planet Mercury, and in today’s post, X is for:


X was the hardest letter to find for this A to Z series.  For a while, I thought I was going to have to do something like “eXtreme temperatures on Mercury,” or maybe “eXoplanets like Mercury.”  There is a crater on Mercury named Xiao Zhao, which could have worked, but we’ve talked about so many craters already.  That seemed boring.  Then, just as I was wrapping up my research, I stumbled upon a paper titled “Modeling the Impact of a Strong X-Class Solar Flare on the Planetary Ion Composition in Mercury’s Magnetosphere.”  I have never in my life been so excited by the title of a scientific paper.

Scientists have come up with something like a Richter scale for solar flares.  The smallest, least energetic flares are called A-class solar flares.  B-class flares are ten times stronger than A-class.  C-class flares are ten times stronger than B-class.  Then, confusingly, we get M-class flares (ten times stronger than C-class) followed by X-class flares (at least ten times stronger than M-class).

Here’s how I rationalize this A-B-C-M-X system.  A, B, and C-class flares are low level flares that are too weak to affect us here on Earth.  We Earthlings can basically ignore them.  The M in M-class flare probably stands for medium. We do need to worry about these medium level flares.  If an M-class flare were aimed directly at Earth, it could damage our satellites, endanger astronauts on the International Space Station, and scramble some forms of radio communications here on Earth.  On th upside, these medium-level flares can also trigger geomagnetic storms around Earth’s poles (a.k.a. auroras).

And X-class flares are eXtreme!  If an X-class flare hit Earth, it could overwhelm our planet’s magnetic field.  Potentially, it could overload our power grids, cause worldwide communications blackouts, and basically wreck the global economy, at least for a few days.  The auroras would be truly impressive, though, possibly extending all the way to Earth’s equator.  So we’d at least be able to enjoy that while waiting for the world’s banking computers to reboot.

Scientists have a pretty good understanding of how solar flares affect Earth.  They’ve also had opportunities to see up close what powerful solar flares do to Mars, Jupiter, and Saturn.  But what about Mercury?  You’d think solar flares would be a pretty big deal on the planet closest to the Sun, but according to the paper I read, we don’t know much about how solar flares affect Mercury.  That’s surprising at first, but it makes sense when you consider how much time and energy (and money) we’ve spent exploring those other planets I mentioned compared to how little we’ve spent thus far exploring Mercury.

Solar flares don’t happen all at once; they occur in phases.  According to the paper I read, when an X-class solar flare hits Mercury, we can expect different elements of Mercury’s exosphere to ionize during different phases of the flare.  Magnesium would ionize right away, during the impulsive phase.  Other elements, like oxygen and helium, would ionize later, during what’s called the gradual phase (also known as the decay phase).  And some elements, most notably sodium, might not be affected at all.

Hopefully more research on this will come soon.  Maybe the BepiColombo Mission will be lucky enough to observe Mercury up close during an M-class or X-class solar flare (I presume BepiColombo is designed to protect itself from that kind of thing).


Here’s the paper I referenced in today’s post.

And here’s a brief article from one of NASA’s education/outreach websites explaining the solar flare classification system.

And here’s another article from NASA that briefly discusses the different phases of a solar flare.