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If a coronal mass ejection with the intensity of the Carrington event1 or more hit Mars, what would happen to an astronaut on its surface who is too far from their base to return to in time? Assuming they have travelled too far in a Mars roving vehicle, and the solar flare hits now, would they survive, or for a limited time? Would the flare knock out the Mars roving vehicle's power unit? Mars has a thin atmosphere and weak magnetic fields.

As for the base, I'm assuming it is underground so that a solar flare wouldn't have much impact there.

1The Carrington Event was a powerful geomagnetic storm on September 1–2, 1859, during solar cycle 10 (1855–1867). A solar coronal mass ejection (CME) hit Earth's magnetosphere and induced the largest geomagnetic storm on record. The associated "white light flare" in the solar photosphere was observed and recorded by British astronomers Richard Carrington and Richard Hodgson. The storm caused strong auroral displays and wrought havoc with telegraph systems. The now-standard unique IAU identifier for this flare is SOL1859-09-01

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    $\begingroup$ This is going to be impossible to answer without making assumptions about the degree of protection given to both the astronaut and the vehicle. If you have some boundaries in mind for those assumptions then it wouldn't be a bad idea to say (e.g. no better protection than apollo landings) though thereafter the astronaut response side of the problem is in medical expertise territory. $\endgroup$
    – Puffin
    Apr 16 at 11:43
  • $\begingroup$ @Puffin Yes, let's assume the astronauts use the same spacesuits used by the Apollo 15, 16 and 17 moonstriders, just less massive so that they weigh the same in Mars' higher gravity. As for the vehicle, let's assume it is enclosed, pressurized maybe. Similar to the ones in the movie "Moon", in case you ever watched it. And we can also assume the astronauts were trained for incidents like this. $\endgroup$
    – Giovanni
    Apr 16 at 12:54
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    $\begingroup$ The areal density of Earth's atmosphere is about 1000 g/cm^2, so if we take Mars to be 1% it will be 10 g/cm^2 which according to this table can stop very roughly 30 MeV protons. The atmosphere is much much thicker than the wall of a spacecraft on its way to Mars. We don't have a proton energy spectrum from the Carrington event, so this will require proton energy information from more recent CME's. $\endgroup$
    – uhoh
    Apr 16 at 21:21
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    $\begingroup$ It's worth noting that there is almost always a warning before a CME occurs, and they take quite a few days to reach Earth, and more to reach Mars (CMEs don't travel at light speed). Only the gamma rays travel at light speed. In other words, before all the particles from the CME come raining down on Mars, there will be enough time for the astronauts to reach their base. This is assuming Solar Activity is monitored of course which it most definitely will be when humans do eventually go to Mars. $\endgroup$
    – Star Man
    Apr 16 at 23:58
  • $\begingroup$ @StarMan Would the astronauts on the ISS have to be returned to Earth if such CME was to come? $\endgroup$
    – Giovanni
    Apr 17 at 5:23
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There is a detailed review of space weather effects on humans in space by Townsend [2021]. They highlight several solar energetic particle (SEP) events that would have exceeded 30 day short-term organ damage limits from recent observations, all of which are likely to be weaker than the Carrington event. They also provide the dose limits for blood forming organs (BFOs), the heart, skin, eyes, and the central nervous system (CNS) for 30 days, 1 year, and career to give the reader a baseline reference. All these values fall in the 250--1500 mGy-Eq (milliGray-Equivalent) range for 30 days. Most of the exposure estimates for recent SEP events like that on July 14, 2000 are >1000 mGy, i.e., you'd exceed a 30 day dosage limit in a matter of a few minutes.

They examine a huge event in 775 AD that would would have caused radiation sickness and/or death in both men and women even with 40 g cm-2 of aluminum shielding (typical values used are ~5-10 g cm-2).

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