Okay, I’ve read a couple of sci-fi books which deal with tide locked planets (i.e. one side of the planet always faces the local sun) and have mentioned them as having an atmosphere that could support human life in certain spots, although the weather was horrific in most places on the planets. Any truth to this?
Second, how close could human explorers get to one of the gas giant planets in the solar system before they had to worry about the effects from the planet’s magnetic field, gravity, etc.?
First question - don’t think there are any known examples of a tide-locked planet with much atmosphere. I’d think it would be pretty hard to get enough conditions right to support human life with the extremes on either side of the planet; for one thing I bet practically all the water winds up frozen on the dark side.
Second question - I think explorers could go all the way down deep into the atmosphere of a gas giant planet without particularly worrying about magnetic fields or unusual gravitational effects, though much more than 1 G would be hard to work with for long. The bigger issue would be the ability to descend into powerful winds and make it back up against such a long steep gravitational field. If you didn’t mind not being able to return home, I think you could descend deep into the planet without great distress.
Actually, there aren’t any known examples of tidally-locked planets, at all. Mercury is in a resonant lock, and Venus is becomming locked, but isn’t quite there yet. We do have plenty of locked satellites, though, and a locked planet is a perfectly plausible possibility. The biggest problem is that anything which can precipitate on the dark side will do so, and then stay there. This will probably include water, and maybe even the atmospheric gasses.
As for Jupiter: The mass of Jupiter is about 318 times the mass of the Earth, so if you were standing on some sort of platform at rest with respect to the planet, and wanted to have 1 g, you’d need to be about 17.8 Earth-radii away from the center, or about 1.6 Jupiter radii. If your platform were at one Jupiter radius, or at about the cloudtop level, then you’d be pulling 2.6 gs. Go any deeper, and you’ll have to worry about winds, atmospheric pressure, and the like, but I think that the gravity is already a big enough problem that you wouldn’t want to.
On the other hand, if you’re in orbit (only practical above the surface), you’ll feel zero gs, just like in orbit around the Earth. Tidal forces will be larger, but still not nearly enough to worry about. The magnetic field will be high, but there are no known health effects from that, and you can shield against that easily enough by making your ship out of a ferrous material (which it probably is anyway). And I can’t think of any other particular dangers that would extend above the atmosphere, so a low orbit around Jupiter should be perfectly safe.
No one’s mentioned the biggest danger: the radiation that’s trapped in the magnetic fields. Jupiter’s magnetic fields are much stronger than Earth’s and thus have much higher amount of radiation trapped in them. If you were in orbit around Jupiter, you’d could get a lethal dose in a fairly short time. I don’t have any hard numbers on it, but perhaps someone else around here does.
That may have been what Chronos was talking about shielding against, because otherwise his statement doesn’t make sense.