Red dwarfs, also known as M stars, are dim compared to stars like our sun and are just 10 to 20 percent as massive.
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Recently scientists found red dwarfs are far more common than before thought, making up at least 80 percent of the total number of stars. The fact that red dwarfs are so very common has made astrobiologists wonder if they might be the best chance for discovering planets habitable to life as we know it. The habitable zone of a star is defined by whether liquid water can survive on its surface. Since red dwarfs are so cold compared to our sun, planets would have to be very close in to be habitable to any life. However, being too close to a star can have its disadvantages. For instance, the gravitational pull of the star would cause tides that could wreak havoc on such a world. Also, young red dwarfs less than 3 billion years old may be very active, firing off flares several times per day, causing ultraviolet radiation to jump by 100 to 10,000 times normal levels and potentially sterilizing the surface of a nearby planet or even helping to strip off its atmosphere. Now scientists find that planets may remain habitable farther away from a red dwarf than once thought. This in turn could mean there is a chance there are far more habitable worlds around red dwarfs than previously suspected. The habitability of a star depends on how warm or cold it is, which in turn rests in large part on how much starlight it absorbs and reflects. Frozen water such as ice and snow reflects light, which means it helps cool planets, including Earth. The researchers modeled how reflective ice and snow would be on simulated planets orbiting two real-life red dwarfs. Ice and snow are less reflective against longer, redder wavelengths, while red dwarfs obviously have fairly red light to begin with. The scientists found that any such planets encircling red dwarf stars would absorb more of their light than previously thought, leading to significantly warmer surfaces. This means the outer edge of the habitable zone around red dwarfs might be 10 to 30 percent farther away from its parent zone than once suggested. Scientists noted that they only looked at the effects of water ice and snow, when other kinds might be important when considering how much energy a planet absorbs and reflects, such as frozen carbon dioxide, nitrous oxide and methane. also, they didn’t look at the effects of atmospheric absorption of radiation by gases such as water vapor or carbon dioxide. That should be done in future.