Here’s another interesting result that has a strong bearing on the Architect of Worlds project:

Super-Earths, M Dwarfs, and Photosynthetic Organisms: Habitability in the Lab

We’ve assumed for a while that the planets of red dwarf stars are poor candidates for habitability, for a couple of reasons.

The main problem is that any planet close enough to a small, cool red dwarf star to bear liquid water is going to find itself seriously sandblasted during the star’s energetic “flare star” era. Without a strong magnetic field – itself unlikely if the planet rotates slowly because it’s tide-locked – it’s going to have a hard time retaining any atmosphere. If there’s plenty of geological and volcanic activity, an atmosphere may reconstruct itself once the primary star settles down.

The more subtle problem is that red dwarf starlight is lacking in the shorter visible-light frequencies driving the kind of photosynthesis we’re familiar with. A red dwarf may produce most of its energy output in the near infrared, which doesn’t do much for green plants. If photosynthesis has a hard time taking off, you’re not likely to get a breathable atmosphere with plenty of free oxygen in it.

The current draft of Architect of Worlds addresses both of these factors, in such a way that it’s actually quite difficult to generate an Earthlike world circling any but the most massive red dwarf stars (maybe M0 V or M1 V, at most).

The paper linked above, though, seems to indicate that this is too conservative. The authors worked with certain kinds of extremophile photosynthetic bacteria found on Earth. They subjected them to simulated red dwarf sunlight . . . and found that the bacteria carried on photosynthesis quite well. Even some of the more common bacteria they tested were able to carry on some photosynthetic activity under simulated red dwarf starlight.

This may be one of those cases where we need to account for the possibility of “life not quite as we know it” being able to exploit a niche we wouldn’t expect. Assuming a planet can retain (or rebuild) its atmosphere after the primary’s flare-star era, photosynthesis that leaves it with plenty of free oxygen in the air may not be as unlikely as we thought. I think one thing I’m going to do this month is to adjust parts of the Architect of Worlds design sequence to allow for this possibility.