The largest population of stars in the galaxy hide in the shadows, too dim to be seen with the naked eye from Earth. Their limited radiance helps to extend their lifetimes, which are far greater than that of the sun. Scientists think that 20 out of the 30 stars nearest to Earth are red dwarfs; however, none of them can be seen with the naked eye. The closest star to the sun, Proxima Centauri, is a red dwarf.
Take the example of the recently discovered planet called Kepler 186f. It orbits a red dwarf star that has only 4% of the sun’s luminosity. It appears to have liquid water and to be habitable and it seems to have gravity similar to Earth. Due to their low luminosity, how do you think lifeforms would look like on a planet like this? There are a lot of factors that need to be considered, and most exoplanets are too far for those factors to be observed directly with current instruments.
Let’s first ponder the possible environments of a planet circling a red dwarf.
What would the sky look like?
For a blue sky: A planet needs to have a thick atmosphere with an abundance of oxygen, and preferably a clear ocean of water or methane. To have a thick atmosphere the planet will need to have a strong magnetosphere. To have a strong magnetosphere the planet will need to have a large, solid iron inner core rotating quickly within a fluid iron outer core. To have such a core, the planet must be larger than a certain size and must have been born after a certain amount of time after the big bang, and in a region of space relatively populated by iron dust created largely through supernovae and nucleosynthesis.
For a red sky: consider Mars. Its atmosphere is 1% of Earth’s and appears red because the ground is red. It’s literally rust. To have such a minimal atmosphere, Mars or any planet would likely have lost its magnetosphere. For that to be the case geological activity and core motion would need to have been dropped nearly to nothing (Mars, in fact, has some magnetism in the southern hemisphere). To be rust the planet must have a considerable amount of iron, so it needs to have accreted during a period when Iron has been nucleo-synthesized in abundance, and it needs to have formed in a region of space in which that is the case.
Let’s assume the planet has the same mass as Earth and is in the circumstellar habitable zone which, around Red Dwarfs, would be very close to the star. Tidal-locking would be inevitable, but models predict that atmospheric equilibration is potentially possible between the starward side and it’s opposite if CO2 and H20 are present. Still, the climate might be pretty turbulent, so expect the need for sturdy shelters capable of thermo-regulation.
The luminosity of a Red Dwarf is no more than 10% of our sun’s, so it will be like living in perpetual twilight. Plants will need to photosynthesize much more efficiently, perhaps via black analogues of chlorophyll.
Life forms could have very similar metabolisms to earthly organisms. But who knows they might not even be carbon-based lifeforms. Metabolisms are a function of the chemical environment they evolve in. A life that evolves in an ammonia-rich atmosphere would be very different than on that evolved in a sulphur-rich atmosphere.
I would think that they would evolve big, big eyes or light sensors. It is logical to assume that their visual system would extend into the infrared end of the electromagnetic spectrum, since a red dwarf’s visible light emission peaks in the red portion of the spectrum.
They would not see colours like we do. They could see inside thick dust clouds, obscured galactic cores, and other hidden regions of the cosmos. These unique abilities are thanks to the infrared light, a wavelength invisible to the human eye.
Space would look like this to them:
This is how they would see us, humans:
How might they observe us?
In infrared, our petty reasons for racism and xenophobic behaviour completely vanishes.
Looking at us humans in the infrared like these aliens would, it would be impossible for them to understand our human failing of unenlightened racism. They would not see the superficial characteristic of white, black, red or yellow skin. In infrared, we would all appear to be the same.
We are all the SAME even when not viewed in infrared but many people still do not understand that.
Their physical size and bodily configuration depend on the gravity of the planet. On the massive planet, massive life forms. The Smaller planet, thinner lighter life forms. If there are aquatic life forms, they are probably on the level of algae and flagellates. Colors of organisms will be in the white to a pale region.
Red Dwarfs are thought to have frequent stellar flares. If you’re caught outside at the start of one, you better have a radiation-resistant coat that will envelop you rapidly.
Check out the free-access special issue on “M star planet habitability” in the journal Astrobiology, , in particular the paper by Tarter et al. NASA and NSF broadly agree, and are funding searches for planets in the M-dwarf habitable zone – have a look at the presentation by Bean at this year’s Exploring Strange New Worlds exoplanet conference –
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