The Theory of Nothing

What kind of planets would intelligent aliens live on?

What kind of planets would intelligent aliens live on?

Astronomers estimate there are a hundred billion habitable Earth-like planets in the Milky Way and fifty-sextillion of them in the universe -- as reported at Extremetech.com.
I don't have a problem with this estimate. There has to be a gaggle of Earth-like planets around yellow, orange and red dwarf main sequence stars like ours, but how many of them harbor intelligent life?
That's a question that all of us want answered, but first we have to determine if intelligent life could develop on the various Earth-like planets that astronomers have recently discovered orbiting around dwarf stars.
I define intelligent life as life that resembles us--humans. It is possible that intelligent life could take on forms that are completely different than humans, but since there is no evidence for this, there's no way to determine whether such life is possible.
First, we have to look at what kinds of stars are best for intelligent life. Our sun is a G-class star in the middle of its main sequence life. A main sequence star is one that's fusing hydrogen into helium. The reason this is important for planetary life is the fact that a main sequence G-class star keeps a more or less constant luminosity during its time on the main sequence. K-class stars, which are redder than our sun, are more populous in the Milky Way and stay on the main sequence for a lot longer than our sun. However, K-class stars have a couple of problems. One is that their luminosity drops over the same period of time that our sun has been around. This means that a planet at a given distance from a K-class star would grow colder, possibly freezing water on its surface. The other problem is that K-class stars are less stable and shoot off more flares than G-class stars. This would represent a danger to life on planets orbiting them unless they had strong magnetic fields.
M-class stars, which are much less luminous and smaller in size, are the most abundant kind of star in the Milky Way galaxy, but planets around them would have to be too close in order to have surface liquid water, and that means that the planet would be tidal locked (have one side always facing the star). Life as we know it would find such a planet very challenging.
One criterion for intelligent life is that the planet it evolves on must be in the habitable zone. The habitable zone is defined as a distance from the star where liquid water is possible on the planet's surface. Liquid water is needed to harbor life, at least life like ours. Fortunately, NASA has found some Earth-like planets in the habitable zones of stars. Habitable zone occupation is the main issue for intelligent life.
Another issue would be the presence of a magnetic field that could protect the planet from being bombarded by harmful radiation from its star. This means that the planet would have to be of sufficient size to maintain a molten iron core over the time needed to evolve intelligent life. This is one of the reasons that Mars doesn't have much of an atmosphere and no liquid water on its surface. Mar's core cooled and quit rotating billions of years ago, which made it lose its magnetic field. When this happened the sun's solar wind blew what atmosphere it had off into space and this made the surface water evaporate into space.
The other issue is the planet's size. If it's too large, intelligent life may mot be able to evolve because of the crushing gravity. Also, if the planet is mostly water then the life that develops may not become intelligent because of the inability to create tools necessary for technology; although, life that develops on these planets may still have intelligence, just not the same as ours.
If intelligent life like ours were to develop on an extraterrestrial planet, the planet would have to look a lot like Earth, with oceans and landmasses that we call continents. It would have to have an appreciable atmosphere that contains oxygen and water vapor. This planet must have a rotating molten iron core not only to maintain a magnetic field but also to cause the formation of land above the oceans.
As for oxygen, it's assumed that plants would evolve on an Earth-like planet orbiting in the habitable zone of a dwarf star. Plants were some of the very first life forms to appear on Earth. Primitive algae-like plants formed the oxygen in our atmosphere, which led to the development of complicated animal life. I would think that this would happen automatically on any such planet.
The development of intelligent life is another matter. This requires the development of a complicated brain. Our evolution did just that, but it took a lot of very delicate climate and ecological changes to help it along, including the asteroid collision that snuffed out dinosaurs and allowed the evolution of mammals.
Could intelligent life evolve in some other manner? The answer is maybe, but we don't have any way to prove that idea. I would think that there are other possible scenarios for intelligent life evolution. Someday, we may find out, but for now, it's just science fiction.
And, speaking of science fiction, in the movie Avatar the aliens were not like us humans. Their habitable moon's atmosphere is poisonous to humans, requiring the use of avatar hybrids to explore this moon-like world. But the main reason that humans wanted to do this is to get at their natural resources. This is a metaphor for the imperialism that Europe practiced with peoples in Africa and Asia that they considered inferior and only useful as slaves. My good friend @Juniverse0 has a race of iteskan creatures in his great science fiction book 'War of Science' in a similar situation. There is a good chance that humans would do the same to aliens on other planets. Hopefully, we will have learned not to do this by the time we go out to the stars.

Thanks for reading.