Red Dwarf Stars Not Suitable for Earth

Red dwarf stars, the runts of the galaxy, probably aren’t so great for nurturing Earth-like worlds, say scientists running new simulations of the formation of planets around a variety of stars.

Astronomers have discovered a huge variety of alien worlds orbiting all types of stars, but one type of star, the M dwarf, has stuck out as one location where Earth-like exoplanets could be nurtured. Red dwarfs are plentiful in our galaxy and many nearby red dwarfs are known to play host to small and (likely) rocky exoplanets. Red dwarfs are long-lived and should there be a suitable rocky world orbiting within the star system’s habitable zone.

Unfortunately, there’s some limitations with this thinking. As the habitable zone around M dwarfs is extremely compact (these stars are smaller and therefore dimmer than our sun, for example), any potentially habitable world would need to orbit a red dwarf very closely. In these cases, the rocky world will likely become “tidally locked” with the star, forcing one hemisphere to endure an eternal day, while the other freezes in an eternal night, certainly not very “Earth-like” in the classical sense.

Also, many of these dwarfs are thought to be tumultuous little stars, erupting with powerful flares that could extinguish any form of biology before it can get a foothold. Already red dwarfs are looking a little unlikely as hosts for Earth-like worlds.

But as the vast majority of stars in our galaxy are red dwarfs, surely, just because there are so many, a few of these red dwarf star systems have formed with the right balance of planetary material and perfectly-located orbits that worlds similar to Earth have been able to coalesce.

According to new research from Tokyo Institute of Technology and Tsinghua University, not so much.

They found that, for an Earth-like exoplanet, with just the right water: land ratio to form around an M dwarf, there needs to be an extremely unlikely balance of planetary material very early in that world’s formative years.