Cyborg IM1 wrote:
Well, I have to admit that GL381 throws all my assumptions about habitable planets out the window.
It appears that this Red Dwarf planet might have TWO habitable planets.
I thought Red Dwarfs had too small of a habitable zone to have multiple planets within it, but not only are there two planets within the habitable zone, but they are both super-Earths.
As long as planets are spaced by ratios rather than fixed distances, the variation in the width of the habitable zone with the luminosity of the star doesn't matter. The inner and outer edges are set by temperature limits and the square-cube law, and vary in strict proportion.
On the other hand, according to Dole the problem with red dwarfs is tidal locking. Tidal force goes with the cube of distance rather than the square, so all planets orbiting in the life zones of the cooler M stars, and those in the inner parts of the life zone of most Ks and the rest of the Ms will get tidally locked to their stars before they can develop a breatheable atmosphere. Dole calculated a diminished life zone of which the inner edge is defined by tidal locking rather than excessive heat, but that is not the life zone that is meant in these discovery reports.
These planets might have habitable temperatures. It is even possible that one star might have three planets with habitable mean temperatures. But I'm old-fashioned: I don't call a planet "habitable" until I know not only that it is warm and cool enough, but also that it has a breatheable atmosphere, significant open water, minimally violent weather and vulcanism, bearable surface gravity, not too much ionising radiation at teh surface, and enough insolation in the B+V band to support [genetically-engineered] crops.