Our little corner of the Universe isn't all that special on the grand scale, but it is at the heart of the Copernican principle. Our Sun is a yellow dwarf, that's peculiar, and one of the major aspects about our planet.
It would be tempting to assume that yellow and white dwarf stars are common elsewhere in the universe. They're not the most multitudinous stars in the universe, and that particular feather is in the cap of a red dwarf.
Red dwarfs make up as much as 75 percent of all stars in the Milky Way, and they are cooler and longer-lived than stars like the Sun. Much, much longer lived.
Our Sun is expected to live around 10 billion years. None of them have yet reached the end of their main lifespan sequence.
Since red dwarfs are abundant and stable, and since we shouldn't automatically consider ourselves to be special, the fact that we're not near a red dwarf should be somewhat surprising. We are near a yellow dwarf.
The Red Sky Paradox is a paper by astronomer David Kipping of Columbia University that questions why we haven't found any other forms of intelligent life in the big wide Universe.
He writes that the solution to the paradoxes would reveal guidance for the targeting of future remote life sensing experiments and the limits of life in the universe.
An artist's impression of a planetary system. The Science Photo Library is owned by Mark Garlick.
There are red dwarf stars that are attractive for the search for extraterrestrial life. They don't burn as hot as Sun-like stars, which means any exoplanets that are close to them need to be hotter. This could make it easier to find and study exoplanets since they are more frequent than the Sun.
Astronomers have found rocky exoplanets like Earth, Venus and Mars in the vicinity of red dwarf stars. Some of them are close. Astrobiologists are looking at it because it seems like red dwarf stars should host life at least somewhere.
In his paper, he lays out four resolutions.
The first thing is that we're just weird. Earth is an outlier if the rates at which life emerges around both star types are the same.
That would cause tension with the principle that there are no privileged observers in the Universe, and that our place in it is pretty normal. It would suggest that our place is not normal.
This answer is not impossible, but it is not particularly satisfying. The answers provided by the other three resolutions are more satisfying.
Life under a red sky was restricted.
According to the resolution, yellow dwarfs are more hospitable than red dwarfs, and as a result, life is less likely to occur around red dwarfs. There is a lot of evidence supporting this idea. Red dwarfs tend to be rowdy and don't have Jupiter-like planets.
There are concerns about the plausibility of complex life on M dwarfs, with concerns raised regarding tidal locking and atmospheric collapse, increased exposure to the effects of stellar activity, and the paucity of potentially beneficial Jupiter-sized companions.
There is good theoretical reasoning to support resolution II.
An artist's impression of a red dwarf. The NASA's Goddard Space Flight Center is located there.
Resolution 3 is a truncated window for complex life.
The argument is that life hasn't had enough time to develop around red dwarf stars.
It has to do with the pre-main sequence phase of the star's life before it starts fusion. For red dwarfs, the star burns hotter and brighter than in this state. A runaway permanent greenhouse effect could happen during this time.
It is possible that the window for complex biology to emerge on rocky planets on white and yellow dwarfs is longer than on red dwarfs.
Although 16 percent of red dwarfs with exoplanets are listed as hosting rocky exoplanets in the habitable zone, perhaps these worlds are not as common as we thought. Our surveys sample the most massive red dwarfs, because they're the most easy to study, but what if the ones we know relatively little about don't have rocky exoplanets?
Since the low-mass red dwarfs are the most numerous, this could mean that rocky exoplanets are less common around red dwarfs than they are around yellow dwarfs.
"In this case, intelligent life is rare amongst the cosmos and is only found between M- and FGK-dwarfs, but habitable worlds are at least two-orders of magnitude less common around M-dwarfs than FGKs," he wrote.
This is a particularly interesting explanation because of the difference between two orders-of-magnitude. It would require that most of the Earth-sized planets around M-dwarfs are inhospitable to life or that the late-type M-dwarfs are rarely host to habitable worlds.
An artist's depiction of a planet in the vicinity of a red dwarf. The Science Photo Library is owned by Mark Garlick.
It's possible that the answer lies in several of these resolutions, which would allow the effect in any one area to be less pronounced. We might be able to get confirmation soon. As our technology improves, we will be able to see the lower-mass red dwarf stars, and look for planets in their vicinity.
If we find rocky exoplanets, we can take a closer look at their potential habitability, determine if they are in the right place, and see if life could have been hampered by stellar processes.
"Resolving the red sky paradoxes is of central interest to SETI and Astrobiology, with implication as to which stars to dedicate our resources to, as well as asking a fundamental question about the nature and limits of life in the cosmos," wrote Kipping.
The research has been published.
