Scientists have suggested several solutions for the red sky paradox. On the image: Artist's impression of the view from an exoplanet in orbit around the red dwarf star Trappist-1. Credit: ESO / M. Kornmesser

Red Dwarf Stars Could Help Solve Alien Life Mystery—10 Things You Should Know

An astronomy professor has suggested several solutions for the absence of habitable worlds around the most common kind of stars.

Astronomers have identified possible solutions to the red sky paradox, which includes the observational absence of habitable worlds around red dwarf stars, which are very common in the Universe and are able to maintain stable luminosity for a long time.

Scientists believe that this may be due to the lack of potentially habitable planets in such stars, a short period of favorable conditions for the development of intelligent life, or inappropriate characteristics of the stars themselves. 

Everything you need to know about the red sky paradox and its connection to the probability of existing habitable worlds

1. The question of the uniqueness of the solar system in terms of habitability has been of concern to astronomers since ancient times. Despite the fact that the Sun’s status as an ordinary star, it is not quite ordinary – the mass of our star is an order of magnitude greater than the minimum mass required for the reactions of fusion of helium from hydrogen, but two orders of magnitude less than that of the most massive observable stars.

2. If we consider the dependence of the habitability of exoplanets on the properties of their parent stars, then we can see that there are much more dwarfs than massive stars, in particular, about three-quarters of all stars are classified as red dwarfs, with masses from 0.1 to 0.5 solar masses, which are able to exist for several billion years, while maintaining a stable luminosity.

3. On the other hand, stars of types O, B, A are not only rare (less than one percent of the stellar population), but also exist only on a scale of millions of years, which may prevent the development of complex biological forms on the planet.

4. Thus, the paradox of the red sky arises, which is formulated as follows: if there are so many red dwarfs and they exist for a long time, then why is the parent star of the Earth a yellow dwarf?

5. In many ways, this paradox is similar to the Fermi paradox: if life is assumed to be common in the universe, then why don’t we see evidence of alien life anywhere?

The gas outbursts from young red dwarf stars could be the reason why planets in orbit are completely inhabitable. Credit: NASA / ESA / D. Player (STScl)
The gas outbursts from young red dwarf stars could be the reason why planets in orbit are completely inhabitable. Credit: NASA / ESA / D. Player (STScl)

6. David Kipping of Columbia University in New York has published possible solutions to this paradox. To do this, he considered the Bayesian probability function concerning the chances of an intelligent observer of F, G, K type stars ( sun-like ) arising on the planet, while the process of the emergence of life and intelligence was considered as a process with a uniform rate. In addition, the author did not consider the possibility of life in exoplanets near brown dwarfs, stars before the main sequence, star remnants, or on orphan planets.

7. As a result, four options for resolving the paradox were proposed. The first is that if intelligent life arises quickly enough, then the advantage of red dwarfs in terms of lifetime disappears, but this solution aggravates the Fermi paradox and contradicts the evolutionary path of life on Earth known today.

8. The second solution is that the probability of the appearance of intelligent life near red dwarfs should be at least two orders of magnitude less than the probability of appearance near FGK-type dwarfs. This solution has good theoretical evidence, for example, in the form of increased activity of red dwarfs or tidal blocking of planets near stars, which leads to a collapse of the atmosphere near the rocky planet.

9. The third solution to the red sky paradox requires that the lifetime of the “habitable window” for red dwarfs be 5 times shorter than for FGK-type dwarfs. This conclusion is consistent with the life span of red dwarfs to the main sequence, ranging from 200 million years to 2.5 billion years.

10. Finally, the fourth solution is that red dwarfs should have fewer potentially habitable exoplanets than FGK-type dwarfs; this version can be confirmed or refuted by determining with great accuracy the frequency of occurrence of Earth-like temperate planets around late-type red dwarfs.

Join the discussion and participate in awesome giveaways in our mobile Telegram group. Join Curiosmos on Telegram Today.


Kipping, D. (2021, June 29). Formulation and resolutions of the red sky paradox. PNAS.
Plait, P. (2021, June 23). The Red Sky Paradox: Why do we orbit a star like the Sun instead of a red dwarf? SYFY WIRE.
Rabie, P. (2021, June 22). A new study on red dwarf stars could resolve the paradox of alien life? Inverse.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

Write for us

We’re always looking for new guest authors and we welcome individual bloggers to contribute high-quality guest posts.

Get In Touch