Red dwarf stars may be able to support habitable exoplanets after all - through complex tidal interactions between star and planet, global magnetic fields could evolve, protecting hypothetical life forms from the red dwarfs' ferocious nature.
GALLERY: The Most Horrific Alien Planets In Our Galaxy
Once identified as the perfect place to search for habitable exoplanets, in recent years, the life-giving reputation of red dwarf stars has taken a downturn. Sure, red dwarfs are abundant in our galaxy and we've spotted many with planetary systems, but the environment surrounding these tiny stars are generally considered to be a bad place for alien life to set up home.
For starters, red dwarfs are much smaller and therefore dimmer (and cooler) than our sun, so the distance a hypothetical "Earth-like" planet would need to orbit the star is much closer than the distance at which the Earth orbits the sun. The "habitable zone" - the region surrounding a star that isn't too hot nor too cold for water to persist in a liquid state on that planet's surface - is more compact around red dwarfs, creating a host of problems.
Although small, many red dwarfs observed are known as "flare stars" - basically angry little stars that generate powerful flares, drenching any nearby planets in powerful doses of radiation. These savage stellar storms, including powerful stellar winds, will likely sterilize any habitable zone planet, ensuring they remain uninhabitable (for biology as we know it in any case). In addition to the horrible stellar weather, planets orbiting within a red dwarf's habitable zone will likely become "tidally locked" with the star; one hemisphere will always be sun-facing, whereas the far side will be in perpetual darkness.
ANALYSIS: Red Dwarf Stars Probably Not Friendly for Earth 2.0
But in new research by University of Washington scientists published in the journal Astrobiology, a planet in a compact orbit around a red dwarf star could receive a gravitational boost that could act as a planetary immune system of sorts, potentially shielding the worst radiation from sterilizing nearby worlds. This mechanism would put red dwarfs back in the life-hunting arena.
It was generally thought that tidally-locked planets were devoid of planetary magnetic fields, like the magnetosphere that surround Earth. But this may not be the case.
While orbiting a red dwarf star, a potentially habitable planet will likely become locked, resigning one hemisphere to an eternity of perpetual light. The close proximity to the star will also result in tidal heating in the planet's mantle - during its orbit, the star's gravitational field will periodically squash the world, driving a dynamo of heating. Much like Jupiter's hellish moon Io, where tidal heating from Jupiter's tides drive the most violent examples of volcanoes in the solar system, these worlds would experience tidal heating, just on a less extreme scale.
This tidal heating may not sound particularly life-friendly either, but it turns out that planets that undergo this form of heating are very good at dissipating heat from their cores. As the cores of these planets cool, the conditions may be ripe for the creation of global magnetic fields.
ANALYSIS: Smartest Aliens May Live Around Red Dwarf Stars
Earth's magnetosphere defends our biosphere from some of the worst solar flares and space weather our sun can muster. So through tidal heating of exoplanets orbiting within the habitable zones of red dwarfs, powerful global magnetic shields may pop up, fending off the red dwarfs' savage stellar storms, possibly allowing the conditions for life to evolve in their protective bubbles.
It sounds counter-intuitive, but it could be that the very thing that would sterilize a world also drives a mechanism that could protect that world.
As we continue our quest to find a bona fide "Earth-like" planet, it's good to know that red dwarfs are not completely out of the running to host habitable planets, especially as they remain our best bet of finding small rocky worlds orbiting distant stars.
Source: Univ. of Washington