This is a hard sci-fi story, so the heroes are outbound from habitable worlds so that I don't have to describe them... yet. Except the question came up on MeWe.
So I need some scale here. Pales and Salus are huge brown dwarfs orbit each other. They are 1460 AU from Epsilon Indi and they orbit each other at a distance of 2.1 AU. They have no anlog in our solar system.
Kawal is named for 2060 Chiron's discover, Charles Kawal. This is a tiny body between Saturn and Uranus and it is classified as a small body and a comet. The ship's AI likes trivia. Additionally, the ship has been to Kawal before. It is fairly old.
Urbian-Adams is very like Neptune, while Minerva and Kawal are like Rhea and Dione. These planets are smaller than our moon and a mix of ice and rock. As mentioned before, there have been a manned mission to both planets.
Iuno Regina is a near Jupiter analog. It orbits much further from the star than our Jupiter. Either it is smaller than Jupiter and orbits at about 9 AU (like Saturn) or is more massive than Jupiter and orbits between 10-20 AU. I have selected the first, smaller mass planet.
Around this planet is Bacchus, which is one of many moons. Bacchus has a dense atmosphere and some sort of liquid on the surface. It is very much like Titan, which would be a good place for humans to have small outposts. There is no life, despite having mud and liquids on the surface. Vera memories take place here.
The trouble spot is Terra Mater. It is just .6 AU from the star. It does have an Earth-like atmosphere, called "The Stuff". Terra is much smaller than Earth, about 85% of Earth's radius but is far more dense. "The Stuff" is largely nitrogen, CO2 and O2. It is not particular dangerous, but also not breathable. Life on the planet has been stuck at Devonian level, where plants first took to the land and fish ruled the sea.
So what is the problem? First, from a story teller's point of view, I have a planet named Terra (Mater) and character named Terra. I need to change that. Second, if Terra Mater is just .6 AU from the Epsilon Indi, I need to cram 3 other planets inside that orbit. This means Apollo and Vulcan must be very low mass and close to the star. No more than 0.15 for Apollo. Neither is as big as Titan.
Duellona is a hell like world at about .25 AU. There are two problems with it. This is too hot and it is in a belt of asteroids. This belt of asteroids is far less dense than our solar system's asteroid belt, but a Venus sized planet sharing orbits with big rocks is not good. In the time line of the story, it known before the colony left Earth. It was visualized by a scout craft and all seemed well. At some point between the flyby and the colonists arrival, it was clobbered by a very large object, maybe several. The whole surface is a magma sea. The colonists have deliberately sent several probes to their doom there. Duellona is interesting but deadly. It is the most telescopically observed object in the solar system, merely for being striking.
The colonists on Terra Mater arrived by massive ion ships. As a consequence of not being able to land on the surface of the Terra and the danger of space rocks from Duellona, the colonists have decommissioned their ships' engines and power plants on any old rock that looks like it could be a danger to the colony. These rocks have been moved to Trojan orbits around Terra.
I figured I would share this world building as it won't appear in my story and will go to waste. The primary purpose of this exercise was character building, which meant limiting the scope of the setting. The heroes are stuck, but not trapped on a single ship going to a planet with no surface. This is the stuff of character building.
As a result of this world building, I have significantly altered my characters, "Terra" in particular. She is now named "Keira" and will feature more prominently in Vera's story.
