5 ms·

There's also the consideration of the host star to take into account. I dislike the term "Earth-like" in these publications because it conjures images of a str

There's also the consideration of the host star to take into account. I dislike the term "Earth-like" in these publications because it conjures images of a strange alien world able to support (human) life. Even assuming there were life capable of withstanding the constant flares from the host star, I suspect it would have to look very different in color and likely composition to the plant life here due to needing to capture a different part of the spectrum.

samatman 5y ago
My education was in chemistry, I've wondered about this topic before. Visible light is actually special after removing the happenstance of DNA-based visual systems from the picture: IR tends to twist or translate bonds (warming) and UV tends to ionize. Visible light being right in the middle is the trick which gives us photosynthesis, and sight, because in both cases a photon can be captured by a photosensitive bond. It's harder to come up with plausible photosensitive bonds for IR light, and most anything is photosensitive once you get far enough into UV.
- JumpCrisscross 5y ago
  > IR tends to twist or translate bonds (warming) Is this unique to IR?
  - samatman 5y ago
    It's almost definitional of IR in fact, but not quite. Waves which are relaxed enough to pass through ordinary matter, but interact in interesting ways with metals and other electron clouds, we call radio. Microwaves start out doing this: usefully, they spin water molecules around, hence microwave ovens. What we call microwaves 'bottom out' on not doing so, it's a useful but somewhat artificial category which I would split between radio and IR if you gave me the gavel. Unlike visible, which is 'visible' because it has distinct properties.
- ncmncm 5y ago
  There is a strong selection bias at work: molecules made and operated on by living systems are chosen according to available energy. A world evolved under lower energies and temperatures would select chemicals with weaker bonds. Other worlds evolved under higher energies and temperatures would select chemicals with stronger bonds. Visible light is visible to us because it is important for molecules we use. This is not to say that all points on the energy continuum are equally favorable to potential metabolic processes, but life adapts to conditions, even where they are not optimal. I don't know of any reason to assume the regime where Earth life has landed is optimal, but it has proven more than adequate.
BMc2020 5y ago
Yes, "Earth-like" caught my attention too because red dwarfs are flare stars. I wanted to check my facts before commenting which led me down the rabbit hole of the history of Proximas flare activity, which is quite interesting. Fun fact: Go outside on a clear night, and you can see 5-10,000 stars. There are 8 times that many red dwarfs in your field of view, and none of them are visible to the naked eye. But in 2016 Proxima was for a few minutes. In March 2016 we saw a superflare: Proxima briefly became nearly a factor of 100 brighter, reaching a brightness just visible to the naked eye from dark sites.

samatman 5y ago

My education was in chemistry, I've wondered about this topic before. Visible light is actually special after removing the happenstance of DNA-based visual systems from the picture: IR tends to twist or translate bonds (warming) and UV tends to ionize. Visible light being right in the middle is the trick which gives us photosynthesis, and sight, because in both cases a photon can be captured by a photosensitive bond. It's harder to come up with plausible photosensitive bonds for IR light, and most anything is photosensitive once you get far enough into UV.

JumpCrisscross 5y ago
> IR tends to twist or translate bonds (warming) Is this unique to IR?
- samatman 5y ago
  It's almost definitional of IR in fact, but not quite. Waves which are relaxed enough to pass through ordinary matter, but interact in interesting ways with metals and other electron clouds, we call radio. Microwaves start out doing this: usefully, they spin water molecules around, hence microwave ovens. What we call microwaves 'bottom out' on not doing so, it's a useful but somewhat artificial category which I would split between radio and IR if you gave me the gavel. Unlike visible, which is 'visible' because it has distinct properties.
ncmncm 5y ago
There is a strong selection bias at work: molecules made and operated on by living systems are chosen according to available energy. A world evolved under lower energies and temperatures would select chemicals with weaker bonds. Other worlds evolved under higher energies and temperatures would select chemicals with stronger bonds. Visible light is visible to us because it is important for molecules we use. This is not to say that all points on the energy continuum are equally favorable to potential metabolic processes, but life adapts to conditions, even where they are not optimal. I don't know of any reason to assume the regime where Earth life has landed is optimal, but it has proven more than adequate.

BMc2020 5y ago

Yes, "Earth-like" caught my attention too because red dwarfs are flare stars. I wanted to check my facts before commenting which led me down the rabbit hole of the history of Proximas flare activity, which is quite interesting. Fun fact: Go outside on a clear night, and you can see 5-10,000 stars. There are 8 times that many red dwarfs in your field of view, and none of them are visible to the naked eye. But in 2016 Proxima was for a few minutes. In March 2016 we saw a superflare: Proxima briefly became nearly a factor of 100 brighter, reaching a brightness just visible to the naked eye from dark sites.