Poster's warning: this will be the second time I've touched upon the subject of solar flares here in Physics Forums, for which I offer my apologies. Nevertheless, I seek clarification about the likely effects of what a seriously powerful flare (or CME) would have, either upon an astronaut in space, or anyone living on a relatively exposed planet like Mars. Here, though, I'm not concerned about charged particles as such; rather my main point has to do with X-rays produced by these solar disturbances. I understand that our thick oxygen-rich atmosphere protects us here on Earth from the worst of these electromagnetic discharges. But what about elsewhere - on the surface of Mars, say? My real point is that any X-ray radiation spat out by the Sun would be propagating across the interplanetary medium at light-speed, which is to say that anyone unfortunate enough to be bounding around on the Martian regolith would receive no advance warning whatsoever. Or am I over-egging the problem (i.e. these X-ray discharges are too feeble to be an issue and/or Mars is too distant from the Sun for this to be a genuine cause for concern)? Thanks again.