I am trying to develop story about the colonization of Jupiter's moons. Io is assumed to have a background radiation of roughly 3600 dayrems. I would guess that other factors such as lunar orientation and elevation could impact this, but let's assume it is a good estimate.

I've looked at several sources that vary in the rem dose needed for acute radiation poisoning and time. Estimates vary between 10 rems to 100 rems with various time exposures.

How long would it take to develop acute radiation poisoning on Io (all other environmentals are accounted for -- assuming you could had air to breath, pressure to keep your internal liquids from boiling...)? The person in question has on normal clothes and is "Jupiter bathing."

How much radiation in rems/minute would you need to develop acute radiation poisoning in a minute? And perhaps an hour?

  • $\begingroup$ I'm trying to clarify multiple sources. Simple math is welcome. $\endgroup$ Mar 16, 2021 at 21:03
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    $\begingroup$ What kinds of protective gear is in use? I'm assuming no one is out nude juppiterbathing. They're all either inside some kind of building, some kind of vehicle or some kind of environmental suit. $\endgroup$
    – elemtilas
    Mar 16, 2021 at 21:04
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    $\begingroup$ Sorry I misread the .gov website's conversion factor, got it wrong by a factor of 1000. $\endgroup$ Mar 16, 2021 at 21:06
  • $\begingroup$ @elemtilas normal clothes $\endgroup$ Mar 16, 2021 at 21:11
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    $\begingroup$ There's a useful chart here for conversions, and I don't think it's that plain sailing imho... news.mit.edu/2011/explained-radioactivity-0328 $\endgroup$
    – Paul
    Mar 16, 2021 at 22:09

1 Answer 1


Advisory: This answer gets quite icky. Nervous dispositions may want to avoid.

Io gets on average some 3600 Rem per day. That's roughly 36 Sievert per day, although the conversion ratio to Sievert depends a bit of the type and energy level of the radiation.

The radiation level also varies quite a bit depending on your orientation on the surface, relative to Io's orbital path.

Dosage: When considered over a period of about a week or shorter, only the total cumulative dosage of radiation matters. It does not matter whether you pick it up in one second, or spread over that week, the damage and health effects are quite similar and related only to total dosage.

Lethality: 2000 Rem+ will kill you within an hour, as your nervous system fails.
A total dose of 500 Rem within less than about a week, is guaranteed lethal without treatment, and quite devastating even with best treatment.
With just 500 Rem dose, death will take a month or longer.
200 Rem will make you sick as a dog, but is unlikely to kill you directly. You may have internal bleeding, you will have extensive tissue bruising and massive gastric upset, as the stomach lining and intestines are exceptionally vulnerable to radiation damage.
100 Rem just about guarantees vomiting, severe gastric upset, purging and fever. Similar symptoms to a severe stomach flu, death unlikely even with no treatment.
50 Rem will make you nauseous, but it could possibly be controlled. This is about the maximum dose where you would still be capable of walking around, working at tasks.
10 Rem or less has no immediate noticeable physical effect.

Shielding: The radiation on Io comes from trapped particles in Jupiter's magnetic field. Plus a bit of x-ray photons from the Jupiter-Io flux tube.
With no Neutrons, and no Gamma radiation, and with all the particles being trapped in the magnetic field and thus not too ludicrously energetic, it can be shielded quite well by a meter of two of water. A basic spacesuit or thinwalled metal ship will not help, it will actually worsen the radiation a bit due to spallation effects.

Assuming no shielding: time to effects.
Io delivers about 150 Rem per hour. 2.5 Rem per minute.

On exposure, you will immediately start seeing tiny little flashes behind your eyelids.
After 5 minutes you will have a metallic taste in the mouth, and a bit of buzzing in the ears, as your blood chemistry starts going off base.
After 20 minutes, you will be quite nauseous, a bit short of breath, and feeling very tired.
After 1 hour, you will be laid out with vomiting, cramps, fever. Your skin will feel as if sunburned, and your guts will begin to purge. You are no longer capable of walking or performing any task.
After 4 hours, you are dead already, your body just needs to complete the paperwork.


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