Hiding from stellar radiation behind an asteroid

[lizvogel]

Okay, I thought I knew science, but after several days of researching this, all I've got is indecision and a headache.

Original fiction, unspecified not-too-far-future time.

My character is the pilot of a small cargo ship in the asteroid belt. (No FTL, no artificial gravity.) Said ship has sufficient radiation shielding to be safe under normal conditions. My idea is that there's an unusually strong solar event (solar flare? coronal mass ejection?), and he has to survive by positioning his ship on the shadowed side of an asteroid (rocks are good shielding), and use his excellent piloting skills to stay there until the storm passes.

1. Does this, theoretically, actually work?

2. I'd like the solar event to be a Coronal Mass Ejection, because some CMEs move relatively slowly, and that gives my character time to make a narratively interesting choice. But is it the CME itself that's hazardous to human life, or a sort of "bow wave" of radiation that precedes it? And if the latter, is that radiation moving at the speed of the CME, or the speed of light? (I keep thinking I have a grasp on this, and then the next source I read contradicts it.)

Guidance appreciated, fellow space enthusiasts!

ETA: Okay, based on comments and additional research the comments inspired, my takeaway is: (1) CMEs can happen with or without accompanying radiation, (2) the stuff in the CME itself is not dangerous to humans, (3) the dangerous-to-humans part of the radiation travels at the speed of light. Which means this story is probably dead; I really needed that longer warning time for the narratively-interesting parts, darn it.

Comments

[mrshamill]

Not a physicist here, but one who has gone down that rabbit hole too. AFAIK, CMEs move quite slowly. And you're right, the radiation precedes it, sort of like a bow wave on a boat. Your MC hiding behind a big chunk of rock should be okay, but it would have to be a *big* chunk of rock. You would have to be careful to delineate any rotation of your big chunk of rock, as that would factor in his shelter. He'd almost have to land on it to ensure he was safe from the radiation and the plasma, which is a significant danger in and of itself. At least he'd be sure to figure out how long to hide, as he would see the CME echoing around his chunk of rock. Wikipedia (where you've probably been) has some excellent source material.

Thing is, they're not really understood well, so you can take quite a bit of poetic license in how he perceives it. I wouldn't stress it too much, just ground it as well as you can and go from there.

[lizvogel]

Thanks! I'm dodging the rotation math by having him not land on it, since the leeward side at the start may not be the leeward side later. But he'll have to stay VERY close to it to stay protected, which adds fun as he has to do constant micro-corrections, dodge any protuberances that may try to clip him as the asteroid rotates, etc. That's a feature, not a bug. (Well, for the story. I doubt he's enjoying it.)

Is your understanding that the bow-wave of radiation travels along with the CME itself? If so, I should be able to give him as much as a week's warning that this thing is coming. But if the radiation's traveling out from the sun at the speed of light, he'll have, what, about 15-20 minutes?

[buttonsbeadslace]

Within the umbrella of "radiation", there might be different types traveling at different speeds. It looks like the magnetic field effects that have damaged electronics on Earth during past CMEs are caused by X-rays hitting our atmosphere, and X-rays are basically a form of light and travel at the speed of light. But the sun can also send out physical particles, protons and electrons, which would be slower.

[lizvogel]

Yeah, and that's what's stumping me: figuring out which types would be reasonable in this scenario, and whether I can hand-wave away the faster types and still have human-life-threatening stuff in the slower types.

[armiphlage]

If the CME has enough neutrons in it, they could make the sun-facing surface of the asteroid radioactive. Nickel-iron asteroids would form isotopes with long half lives, and not be interesting to the plot. Surfaces of silicon-rich asteroids could generate 31Si with a half-life at 157.2 minutes.

The protagonist could think themselves safe hovering in the shadow of the asteroid ... until their radiation alarm goes off. They'd be puzzled, until they realized the rock beneath them was recently exposed to the CME, and was now giving off beta radiation. They'd have to move farther away from the surface (dose decreases as the square of the distance to the asteroid's surface), but would risk leaving the penumbra of the asteroid's shadow.

[white_aster]

Ok, FWIW, that is an AWESOME use of science as plot and I would love to read a story that took the science that seriously. :D

[white_aster]

Also Not That Type Of Scientist, but I think that probably the "space weather forecast" or whatever sensors he's using to detect the CME would probably be focused on "this is the part that can kill humans/their ship" - so it would likely project warnings both for the radiation bow wave and the CME Ejected Crap itself. As an author, I think you can assume that the pilot would have a computer-generated timeline tagged to warnings about both of these things. And as I think others have mentioned, the radiation would be moving considerably faster, though I'd say do some quick back of the napkin estimates and call it good. Most readers won't be able to do that math themselves, so coming up with something that mostly sounds reasonable is all that likely matters (so says such a reader).

[lizvogel]

Oh, yes, I figure there's all kinds of space-weather forecasts in this universe, so he'll have as much warning as physics allows for either/both. The timing question matters because if he has fifteen minutes' notice, he'll be making very different choices than if he has a week's notice.

Sadly, the target market is a hard-SF anthology, so I have to assume the average reader (and the editor) will know at least as much about this as I do, and probably a lot more.