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Cheap Astronomy
2014-Oct-19, 07:41 AM
Hi, I'm trying to answer a question about radiation from Jupiter. This is what I think is right, but please correct if I am on the wrong track:

As far as electromagnetic radiation goes, Jupiter radiates more heat than it receives from the Sun, largely in infra-red / radio and this is largely the result of gravitational compression. The vast majority of visible light from the planet is reflected sunlight. Any ionising radiation from the planet is largely the result of high-energy particle-to-particle interactions in the magnetosphere - so these are more point sources than global radiation. We have some detected persistent x ray sources of this kind.

The 'dangerous' (e.g. to visiting spacecraft) radiation that is often discussed in relation to Jupiter is largely high-energy sub-atomic particle radiation, where particles are whipped up to high velocities in the magnetosphere of the rapidly spinning planet. The bulk of these particles come from Io's volcanic outgassing, so involves a lot of sulphur and oxygen ions, as well as protons (hydrogen ions) and electrons. Collisions with such high energy/high velocity charged particles is what will damage a visiting spacecraft.

All comments welcome.

Thanks,

Steve

tusenfem
2014-Oct-19, 09:15 AM
Hi Steve,

Yes, all-in-all you got it pretty right there.
Heat emission is because of contracting, Jupiter is still not in equilibrium. I don't have my Jupiter presentation on this laptop, so I don't remember the number anymore how much Jupiter shrinks per year.
What we see from Jup's surface is reflected sunlight, unless you are watching the aurora of course.
The radiation is mainly caused by high energy electrons. The ions are easier to shield off in a spacecraft, but for humans on Europa (All these moons are yours except ...) then the ions (mainly protons, sulfur, oxygen) are also dangerous.
Near Io collisional ionization is most important, further out in the magnetosphere UV ionization also becomes important.
One way of energizing the electrons (and ions) is through the magnetosphere-moon interaction, which generates a potential drop over the moon. Currents flowing in the ionosphere need to be closed, and they do that along the magnetic field. Far from the equator the density is very low, and thus the electrons need to be accelerated (because the current needs to be conserved) and electric fields are created, energizing the electrons (Hannes Alfvén's double layers).

If you have more questions do not hesitate to send them.

Cheap Astronomy
2014-Oct-20, 10:43 AM
Thanks. I get the impression from your answer that the electrons are more 'damaging' that the ions (which are easier to shield off). Is there a reason for that - or is it just because there are more electrons than ions?

Steve

tusenfem
2014-Oct-21, 06:29 AM
just give me a moment more, I am looking for the correct person who can give me an image showing spacecraft shielding parameters