Red Dwarfs Could Sterilize Alien Worlds of Life 76
astroengine (1577233) writes "Red dwarf stars — the most common stars in the galaxy — bathe planets in their habitable zones with potentially deadly stellar winds, a finding that could have significant impacts on the prevalence of life beyond Earth, new research shows. About 70 percent of stars are red dwarfs, or M-type stars, which are cooler and smaller than the sun. Any red dwarf planets suitable for liquid water, therefore, would have to orbit much closer to their parent star than Earth circles the sun. That presents a problem for life — at least life as we know it on Earth, says physicist Ofer Cohen, with the Harvard-Smithsonian Center for Astrophysics. Cohen and colleagues used a computer model based on data from the sun's solar wind — a continuous stream of charged particles that permeates and defines the solar system –- to estimate the space environment around red dwarf stars. 'We find that the conditions are very extreme. If you move planets very close to the star, the force of this flow is very, very strong. Essentially it can strip the atmosphere of the planet unless the planet has a strong magnetic field or a thick atmosphere to start with,' Cohen told Discovery News."
Re:Renaming (Score:5, Interesting)
Scientists might want to rethink the moniker "habitable zone" if it is filled with a deadly amount of stellar radiation...
The habitable zone only refers to the amount of heat radiation a planet receives it does not mean that every large rock there is habitable - just look at the moon. There are additional constraints for a habitable planet e.g. requires an atmosphere and liquid water. All this result does is to add an additional requirement near a red dwarf: you don't just need a gravitational field large enough to hold onto an atmosphere you also need a magnetic field to shield it.
Re:Frist (Score:4, Interesting)
At planetary distances tidal locking is a relatively slow process dependent on the angular diameter of the planet as seen from the stellar core and the the magnitude of the gravitational force. Witness Mercury whose day is, after 4+ billion years in close orbit around a relatively massive star, still only 66% as long as its year.
Actually though tidal locking is not necessarily a problem - atmospheric models suggest that mixing would prevent the temperature imbalance from becoming too extreme. Of course you would end up with several very different ecological niches. Obviously photosynthesis would be impossible on the dark side, but that was a relatively late addition to the game on Earth, and there are plenty of other metabolisms available. Meanwhile the light side wouldn't have to deal with that pesky dark period, and the twilight zone would likely have pretty strong, steady winds from which life could potentially extract energy. Of course that's only relevant after complete locking - but then red dwarfs are essentially immortal, so as long as the planet manages to keeps its atmosphere life should have plenty of time to evolve to the conditions available.
The biggest problem I see with tidal locking is its potential impact on the magnetic field protecting the atmosphere, as it's believed that Venus and Mars have only tiny magnetic fields in large part because of slow currents in their cores.
Of course there's also the possibility of the moons of gas giants around red dwarfs. Thanks to the thermal emissions of the gas giant they could be at least a bit further from the sun, as well as getting significant protection from the gas giant's potentially much larger magnetic field. They would also have the benefit of tidally locking to the planet rather than the sun, so they would still experience a diurnal cycle, though it might be a bit slower than Earth's. Io for example orbits Jupiter in 1.7 days.