I was watching the first episode of The Universe series on Blu-Ray yesterday, and they talked a bit about solar storms and their potential risks (overloading powerlines, possible dangerous levels of radiation exposure for airplanes in flight near the poles, etc.).

A bit more reading on the subject suggests that solar storms are a serious risk to astronauts in orbit around the Earth or on the Moon.

I'm wondering, though, at what distance from the Sun do solar storms cease being dangerous to astronauts?

If astronauts were orbiting one of the outer planets, would a solar storm still present a serious risk of radiation exposure?

Hi Robonaut. Good question. My two cents:

The degree of danger depends on four things:

1. The type of solar event you consider. There is the 'normal' solar wind, which you may regard as baseline solar weather. From time to time, this wind gets supplanted with stronger events such as solar flares or coronal mass ejections.

2. Regardless of the event, danger rapidly decreases with increased distance from the Sun. This is because incident radiation follows an inverse square law. It drops off in proportion to distance from the Sun, squared.

3. Some types of solar output can be directional. Coronal mass ejections are one. If you're not in it's path, you'll obviously be ok.

4. Planetary magnetic fields play a very important role. Magnetospheres tend to collect and concentrate whatever radiation is out there. The Earth's magnetosphere, and consequent geo-magnetic storms, raise the risk in the near-earth environment.

So- the outer planets. You have a greater distance from the Sun (2), but they all have magnetospheres (4). Jupiter has the largest one by far. On top of this, Jupiter, together with it's moon Io, also produces it's own radiation. On balance, adding all this up, the Jovian environment is very dangerous.

Please note: This may not be entirely accurate. I'm no expert.

And of course, sometimes it gives them superpowers...

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PreadSt.
I'm not sure you're fully right about the inverse square law (ISL)!
That applies to radiation, but the solar wind and flares are particles.
They would spread out in a way that is equivalent to the ISL, but being charged will follow lines of magnetic force. So flares will tend not to go towards the solar poles.
And could the magnetospheres of the planets cast a "shadow", which could protect spacefarers?

John

Or, the magnetosphere, lowers risk by providing protection.

It depends on where the astronauts are located. It protects us surface dwellers. It adds protection for the astronauts in the ISS and the low-Earth orbits. It would even at times protect astronauts on the moon (University of Washington press release: Earth's magnetic field could help protect astronauts working on the moon).

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I knew I'd missed a few things.

Re ISL- I assumed that applied to particles spreading out too?

1.732245395 billion miles. Within that distance, they're toast, not only from the massive genetic damage, but burned to a crisp, literally.

But at 1.8 billion miles, it's like sipping lemonade on a warm Sunday afternoon...

Ok. That's an exaggeration. In reality, it would depend on the strength of the solar storm, which vary widely.

It could, if the storm were strong enough, though it's less likely that far out.

The radiation hazards of deep space fight by humans is not publicized that much by NASA and space advocates. It is a real danger and will require mitigation measures before we can commit to sending people for extended periods beyond our magnetosphere. There are aready studies for solar flare alert instruments for when we return to the Moon. The instruments will alert astronauts in enough time for them to find shelter to avoid fatal exposure from the intense radiation from massive coronal mass ejections (CME) from the Sun.

For Mars-bound astronauts, perhaps they will store their water in a jacket around the crew compartment in order to provide protection. Or they could engineer a smaller "safe" compartment inside a large water tank.

NASA and space advocates talk about radiation hazards, and their mitigation to an acceptable level of risk, a great deal.

Jon

To protect against the sun you only really need a shadow shield, basically a dense parasol. There are other radiation risks, such as that from cosmic rays, which would require different countermeasures, including a shield to surround the crew. However, neither of these systems necessarily have to be deadweight, as a proper design might use them to perform double duty at some point in the mission.

Eventually, we may have interplanetary cyclers that have heavy-duty purpose specific shielding, but since they merely cycle in convenient orbits instead of start and stop at specific destinations, the deadweight penalty for the initial acceleration isn't really important.

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One layer of aluminized mylar will not protect you from protons in a CME....

Who said otherwise?

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In my book, a dense parasol is like to the one put up by the Skylab 2 crew (Conrad, Kerwin & Weitz). It was a thermal shield only, not designed to stop solar flares.

Oh, I haven't read that book. I'm not using a specialized definition of the term "dense parasol". I merely mean to refer to a shield that is parasolic and dense enough for the job referred to by context.

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