If life did evolve on a planet around a blue star, what sort of adaptation could be expected? I so far have the autotrophs being yellow/orange or blue to absorb the light. I also thought the animal life would have blue reflective skin.
1$\begingroup$ Please, pay attention to the tags you select: what do you expect an expert in "blue" to know? $\endgroup$– L.Dutch ♦Apr 28, 2022 at 4:58
5$\begingroup$ here is an interesting article on why plants (on Earth) are green. TLDR - most of the solar energy is in the green part of the spectrum, so you'd expect the plants to absorb most of that. But it turns out that absorbing all that energy would make the chemistry of photosynthesis too unstable, so the plants reflect some of the green light. So if plants on your planet follow a similar pattern then the part of the blue star's spectrum with the highest intensity will be your plants' color. $\endgroup$– GiantSpaceHamsterApr 28, 2022 at 13:50
Physical adaptations would be less about hue and more about shielding. Colors would tend to be darker - consider that albinism is more dangerous and susceptible to more radiation damage. This article on plant color has some interesting insight. Instead, indirect light blocking would be a bigger deal, such as heavy fur, scales, or shells. With higher solar flux, body heat regulation might also be a higher priority, of which there are many different strategies. A shiny exterior would have more to do with heat dissipation than damage protection. For that, any opaque surface will do.
Also, light-averse behaviors would be much more prevalent - burrowing underground, keeping to shade, crepuscular and nocturnal rhythms, etc. I would expect greater differences between night and day in general. Cloud cover, weather, and water evaporation rate may have a greater impact on the landscape and animal behaviors (though weather specifics belong in a separate question). Creatures capable of tool use might learn to build parasols! Plants might actually worry more about too much light than not enough. You might expect an oasis of more vibrant life in a shaded area instead of a well-lit area.
Ocean life could thrive, as there would be more available space that is warm and well-lit, while still shielded from much of the more harmful wavelengths. High altitudes and deserts could be more harsh, though on earth creatures still make a living there. Perhaps life in those climates on earth could offer some more inspiration.
If your planet has much axial tilt, creatures might find reversed seasonal relief in higher latitudes - perhaps life there hibernates through the summer and blooms in the fall and winter. It may also shift the most vibrant life away from the equator and bring more deserts there. However, these locational effects would depend greatly on where in the goldilocks zone the planet rests.
1$\begingroup$ I don't agree that colors would be darker. Albinos completely lack pigmentation, but most pigmentation is for blending, not for protection from the sun. Melanin didn't exist until about 1.2 million years ago, and it's a side effect of our folate metabolism. I believe that's too specific to generalize into alien life. $\endgroup$ Apr 28, 2022 at 21:25
$\begingroup$ With respect, do you have sources for this information? $\endgroup$ May 2, 2022 at 3:27
$\begingroup$ I just based most of these ideas on the practical fact that a strong blocking surface is what you need to protect against radiation. Color depends on the frequencies of light absorbed vs reflected, and a pigment that absorbs more frequencies is more effective at what it does. Reflecting kicks the energy out, but an effective reflector must be smooth and only helps on the surface. Absorption can occur through the depth of a material and doesn't have to be smooth. The difference is how they handle heat (bbc.co.uk/bitesize/guides/zr7j382/revision/4). I did add a source on plant color. $\endgroup$ May 2, 2022 at 6:54
There are way more factors than just the classification of the star in picking the adaptation of the organisms living under it. And don't forget that the color in the star name only indicates the predominant color, but stars emit on a continuous spectrum, not on a narrow line.
Our sun is a yellow dwarf, yet we have white bears, black crows, brown bear, red scorpion fish, blue jay, green lizard and so on.
Also autotroph-wise, we have green plant, blue algae and even red ones.
In short, life would adapt to the specific environment where it is settling.
There is a serious doubt that complex life could evolve near a blue star. Conventionally, stars of classes O and B are called blue. According to the table here https://sites.uni.edu/morgans/astro/course/Notes/section2/spectralmasses.html and the calculator here https://rechneronline.de/planets/lifespan-star.php , the lifetime of the smallest B-class star is less than one billion years, which is, if our life on Earth is any indicator, not enough even to develop multicellular organisms. Even if we stretch the definition of blue to the late A-class stars, we have only 3 Gyr, which is also not very impressive given that this is around the timeline of apperance of multicellular life on earth. However, it will not come to that most likely, since the change of the luminosity of the star nearing the end of its main sequence life will probably boil or evaporate all the oceans on the planet long before that. For comparison, this is supposed to happen on Earth around one billion years from now, which makes around 5.5 Gyr of the Sun's projected lifespan of 10 Gyr suitable for life.
$\begingroup$ We have a thing here called a frame challenge. We like it if when telling the OP it won't work if you can propose an alternative solution. That being said, the question is problematic in that a proposed solution which allows life isn't mentioned - just assumed. In such cases it's sometimes best to just go along with it and pretend it might work. $\endgroup$ Apr 29, 2022 at 20:10