Habitable Planets With Earth-Like Biospheres May Be Much Rarer Than Thought

Short form : Earth-sized planets made out of the right amounts of the right stuff might exist in their bajillions, comfortably orbiting within their stars habitable zones. But the majority of stars out there are smaller and cooler than the sun. Normally this has the problem of tidal locking the planet tot he star, but if the planet escapes that fate (by having a moon, or orbiting a large-enough small star to avoid tidal locking) there’s another problem. Cooler stars put out a different spectrum of light. Even if the watts-per-square-meter of light is the same as on Earth, if the spectrum is wrong, photosynthesis using known systems might not work. Consequently, if life arises on a planet orbiting a red dwarf, it might not evolve adequate photosythetic systems to transform the planet, as life on Earth took a few billion years to do.

This might also mean that an Earth-like world could be located and terraformed and seeded with Earth-life… only to have the plants sicken and keel over.

Genetic modification might or might not fix this, depending on whether or not photosynthesis using redder spectrums can be made practical. Another approach: if humanity has the ability to cross the gulf between the stars, we can do lots of other stuff. This should include parking fusion reactors in orbit and using the generated power to create the biologically necessary frequencies of light. A giant UV flashlight in the sky, parked in geostationary orbit right in front of (or next to) the sun.