IFL SCIENCE
Arguably the largest question in the search for life beyond our Solar System is whether there’s any point looking at these common M-type stars, known as red dwarfs. This category makes up three-quarters of the galaxy’s sources of light. It’s an even larger share once you exclude the massive stars with life spans too short to allow life to develop, and also includes most of the stars close enough for us to really study.
The TRAPPIST-1 system – seven rocky planets orbiting an M-type star just 40 light-years away – is ground zero for this debate, with three planets in the zone where temperatures are currently suitable for life to survive.
Unfortunately, objections have been raised arguing that any planets in the “habitable zones” of red dwarfs would long ago have lost their atmospheres, making them not habitable after all. If so, we’re probably wasting our time investigating these systems for signs of life and need to focus our energies on the few F, G, and K-type stars we can see well.
The problem is not just that many red dwarfs are flare-y stars whose outbursts may have stripped off any atmosphere, but that M-type stars undergo a hotter stage early in their development. This, combined with runaway greenhouse effects from water in the planets’ atmospheres, would have turned the entire crust molten, causing any water trapped in rocks to escape. If this stage lasted long enough, as most things do with such slow-changing stars, all the water in the atmosphere would escape to space. Under such conditions, there would be no prospect for volcanic restoration of the planets’ atmospheres once the star cooled sufficiently to allow them to survive.
A new model of the atmospheres of planets in the TRAPPIST-1 system rejects the theory they would ever have gotten this hot. Previous modeling had, for simplicity’s sake, treated the atmospheres of the TRAPPIST-1 planets during their star’s hottest phase as purely convective.
Connect with us on our socials: