How common are habitable planets?

In the BSG universe, it looks like nice planets are rare. As the fleet moves through space, it is regularly sending out scouting missions in Raptors, searching for food, resources and fuel. Depending on fuel available, I presume that means scanning thousands of planets. But what planets do they encounter?

  • They start at their own colonies, which seem quite nice.
  • First, Kobol, which they are guided to, it seems, by the Cylons. Leoben tells them they will find it. It’s no accident. Of course, Kobol is not a new, undiscovered planet.
  • Next, New Caprica. This discovery elicits great excitement both as the first such planet seen, even though it is barely habitable. It is also exciting for being somewhat hidden.
  • Next, the Algae planet with the Temple of Five. This planet may not be strictly habitable. It seems very harsh, but it does have a food source.
  • Finally, Earth, which of course at one point was a perfect planet, being the homeworld of humanity after all. It’s now ruined by nuclear war.

12 Colonies? Not likely.

The colonies are a bit of an issue. Moore says he imported the idea of the colonies — 12 colonies at one star system — from the original series, knowing that this is not actually realistic. How can we retcon it as realistic? The problem is a typical star can only have perhaps 2 planets in a comfortable temperature zone.

  • The easiest explanation would be to say colonies are not planets, but continents. Then they could exist on far fewer planets.
  • Ordinary double star systems are not stable for planets, but a very distant binary could hold planets for long enough. Eventually the other star distorts the orbit of the planets.
  • If you have a superplanet (gas giant) in the habitable zone, you could have 12 moons in orbit around it, all in that zone. Or with two stars and two supergiants in the zone, you could have 3 moons per supergiant, and get 12 moons.

Now this is highly improbable unless you use terraforming. And it might make a lot of sense that the Kobolians, when expelling the 12 colonies, did just that to make a home for them.

The Algae Planet

While we don’t know this is truly habitable (it seems not) they are clearly guided to this planet, to be there at one magic time planned thousands of years in the past. As Baltar says, the odds of them all converging on that planet are astronomical. He tells them all to be aware that it’s not chance. No, they don’t come here by accident. In fact, the fleet goes past this world (scanning it and noting it) but then, by strange coincidence, their food processors are all contaminated. They have no choice but to take a dangerous trip back to get there now, now, now. This can hardly be chance. Somebody pulling the strings — using agents on the fleet — contaminated that food.

New Caprica

It seems they discover New Caprica by chance, and it’s hidden. But do they? It’s discovered by a random jump. And they are way too early for their appointment at the Algae Planet. They powers that be need them to wait 18 months. Remarkably, an excuse appears. Head Six pushes Baltar to run for office and halt the fleet there.

Then, remarkably, a year later the Cylons see the flash of the nuclear bomb that Gina, a Cylon, set off after Baltar gave it to her at Head Six’s encouragement. Is it chance this happens? Or is a Cylon scout directed somewhere 1LY away to see the flash? The string-pullers need the fleet off the planet now, and events all conspire to make it happen.

So no, I don’t think the detour to New Caprica is an accident; in fact it’s a must to time their arrival at the Nova, to have Tyrol open the Temple of Five, and to have the chosen one activate it — oops.


Their arrival at Earth is totally manipulated by the Final Five. And of course it is not a planet they discover.

So the conclusion? They never find a habitable planet on their own, and in spite of a lot of searching. So in this universe, they are quite rare, which also explains why Kobol and the colonies are so far from Earth.

I should also note that this is spelled out in the original miniseries script:

LAURA Can we really find another planet to colonize?

ADAMA It may take a while. The number of planets that can sustain human life is very small. And there’s always the chance they may already have some kind of indigenous intelligent life on them — although if there are aliens out there, they’ve been awfully quiet.

In that script there was only one planet (which they called Kobol) and all 12 colonies were on it. There was only one star system, and FTL exploration was rare — they had not explored more than 30 LY outside their system.