Wondering if anyone has any different ideas on this one or any thoughts. I've recently started thinking about the issue of where humans could go. Mars is the obvious next step in space exploration, and of course asteroids are a possibility too. But what after that? Surely humans can survive flybys of most of the bodies in the solar system. The more distant areas would require some kind of heat source (probably nuclear) but what about landing?
Here's my list. Feel free to disagree. Basically it comes down to what a reasonable space suit could be expected to protect one from, because just landing there in a super-heavy armored pressure vessel seems rather non-useful.
Mercury: Maybe on the cool side, for a limited time at least. On the side facing the sun would be difficult. Maybe with large sun shades to protect astronauts for a brief period of time.
Venus: Unlikely. A very hard, very pressure and heat resistant suit would be necessary. Extremely robust heat rejection system. The only probes that ever landed on Venus functioned only a short period of time. Venus is probably a no-go.
Earth's moon: Yes. It's been done.
Asteroids: Yes. Of course, deep space exploration would have other issues to contend with, like radiation shelters for sun storms, but there's nothing about an asteroid that makes it impossible to explore by humans. Would be difficult to stay on surface due to limited gravity, so it would not necessarily be "walking" on it so much as clinging to it.
Comets: Probably not, unless very distant from the sun and thus very cold. They spew out a lot of vapor, debris and so on. Not an appealing place for humans.
Moons of Mars (Phobos and Deimos): Yes, but again, small size and thus gravity makes motion and maneuvering an issue. Not simple to "walk on"
Major moons of Jupiter: Maybe or Probably. Nuclear heat source for human habitation would likely be necessary. There is a thin atmosphere which contains oxygen that could potentially be extracted, which would be an interesting possibility. Space suits beyond the current capabilities would likely be necessary, but not impossible. Some areas may have hazards that would be beyond current systems.
Major Moons of Saturn: Maybe. Even colder than those of Jupiter. Similar hazardous areas, but possible some areas could be habitable.
The gas giants: No. You would die very quickly.
Pluto and keiper belt planetoids: Maybe. Again, very cold. The big issue would be getting a crew to and from them. Presumably not a good place for a settlement, so a one-way trip would be something nobody seems likely to want. Extreme distance would be the big problem with current technology.