[Space] Making a solar system with 3 (semi-) habitable planets?

[BaHalus]

Originally Posted by Daigoro

Would it be acceptable for the outermost planet to get most of its heat from volcanism rather than insolation?

In the last estimatives I knew about life on earth, about 2/3 of the life in our planet gets its energy from the earth, not from the sun. Of course, it is mostly archaea and bacterias, but there are ecosystems based in geothermal energy that includes macroscopic beings as well. The greenhouse effect can give a huge contribution too, to warm things up. Not sure, but I think that if you exchange mars and venus places you could get more pleasant planets.

Anyway. I've heard that venus could have life in its clouds and mars in its underground. Many satelites are good candidates for life, despite distance from the sun (gravitational tides produces a good amount of heat in some of them)