The Paradise of the Red Sky reveals how rare life on Earth is

Our Sun is a yellow dwarf and because man evolved in orbit around it, it makes sense to assume that such stars are common in the universe. But the truth is that the most common stars are the red dwarfs, covering 75% of all the stars in our galaxy. They burn at lower temperatures and live much longer than stars like the Sun.

The Sun is estimated to have a lifespan of 10 billion years, while the red dwarfs have trillions of years. In fact, no red dwarf has reached the end of his life since the creation of the universe, 13.4 billion years ago.

So since red dwarfs are so numerous and so stable, why do not we live in orbit around one of them or why have we not found other species of intelligent life there? There is a paradox here that contradicts the Copernican principle which states that the Earth is nothing special and that it is a mediocre planet in an ordinary solar system.

The study of red dwarfs is a promising case for finding extraterrestrial life. We know that they burn at lower temperatures and have rocky planets in orbit in the habitable zone, which due to temperatures is closer to the star. This makes them easier to spot.

Scientists have four suggestions in response to the Red Sky Paradox. The first is that life on Earth is very rare, with a chance of being only one in a hundred. This of course contradicts the Copernican principle.

The second is that yellow dwarfs are more suitable for life than red dwarfs and as a result life around red dwarfs is one hundred times less likely to develop. There is some evidence to support this. Red dwarfs, for example, are highly active in solar flares, and have no planets like Jupiter in their orbit that work for the benefit of the surrounding planets by protecting them from asteroids.

The third case is that life simply did not have enough time to develop around red dwarfs. Red dwarfs need more time to start burning hydrogen, so by then they burn at higher temperatures and are brighter. During this time, a permanent greenhouse effect would prevail on potentially habitable planets, which in turn would mean that the complex biology development window would be much smaller than that of the yellow dwarfs.

The fourth case says that 16% of red dwarfs have planets in the habitable zone and may be the exception to the rule. Given the small mass of red dwarfs, planets in habitable zones are one hundred times less likely than planets in habitable zones of yellow dwarfs. We have observed the largest and brightest, but the majority may not have rocky planets in the habitable zone or for some reason the planets around the red dwarfs may not be able to accommodate life.

The answer can be found in a combination of these cases. As our technology improves, we will be able to better observe small red dwarfs and the planets around them.

The Red Sky Paradox solution is crucial for astrobiology and SETI, as it will tell us which stars to commit our resources to when asking basic questions about the nature and limits of life in the universe.

The research was published in PNAS.

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