Redefining habitable zone for advanced Terran animals

[AstroChara]

This article suggests that other than the 'too much carbon dioxide' problem that plagues the outer worlds which need a lot of them to maintain warm-enough temperatures, red dwarf Earthlike worlds may have too much carbon monoxide, which is created by the type and intensity of UV radiation from those stars. More in the article...

[stevebowers]

High levels of CO2 and even of CO need not rule out complex life, but it would rule out complex life as we know it. Settlers on worlds like this would need to be radically tweaked to survive such conditions, or would need to have sophisticated environmental technology to stop the toxic gases from reaching them.

[AstroChara]

High levels of CO2 and even of CO need not rule out complex life, but it would rule out complex life as we know it. Settlers on worlds like this would need to be radically tweaked to survive such conditions, or would need to have sophisticated environmental technology to stop the toxic gases from reaching them.

Exactly! And another way to deal with this, I assume, is to somehow prevent this UV light from reacting with the atmospheric gasses in the first place.

[Drashner1]

Is there any particular physics/chemistry based reason that CO couldn't play a role in an alien biosphere similar to (or even radically different from) the role that CO2 plays on Earth? Meaning that it takes an unlikely amount of energy to deal with its chemical bonds or its structure makes it much harder for it to bond in ways that would support some form of life form or something.

I'm also reminded of an article I read many years ago about - not exactly a chlorine atmosphere world (once a staple of science fiction), but a world with a percentage of chlorine in its atmosphere - that might be capable of supporting life. IIRC water on such a world would be rather like vinegar.

Might something in the same general ballpark apply here? Not a chlorine atmosphere, but some environmental mix that would be 'tougher' than Earth's biosphere, but still operating on biochemistry that seems workable.

On another note - would the increase in UV also result in an increase in ozone in the upper atmosphere that might mitigate the production of CO?

Just some thoughts,

Todd

[stevebowers]

I'm quite keen on the use of Lagrange sunshields and magshields to protect planets in high-energy environments. A large semitransparent or relatively opaque shield or swarm placed between the star and the planet could absorb starlight and re-emit it at acceptable strengths and wavelengths, while also incorporating a magshield if necessary. One major problem would be damage and displacement by superflares or CMEs; but it seems likely that this sort of problem would be relatively minor compare to the effort required to place the shield in the first place.

[Avalancheon]

There have been many studys attempting to estimate the habitable zone for an Earthlike planet. The validity of the broader estimates (such as those proposed in the 1993 Kasting study) is dependent on the silicate cycle stabilising a planets climate. However, the silicate cycle can only operate when there is a significant amount of continental crust exposed to aerial weathering.

The 2008 Flament study suggests that ancient Earth was an ocean planet that was 99% covered in water. Thus, we know that the silicate cycle could not have played a factor in regulating its climate. If we assume that all Earth-like worlds start off as ocean planets, we must by necessity conclude that the broader habitable zones (as proposed by Kasting and others) are implausible.

This recent study by Schwieterman is just another nail in the coffin for such estimates.

[Avalancheon]

On another note - would the increase in UV also result in an increase in ozone in the upper atmosphere that might mitigate the production of CO?

Just some thoughts,

Todd

An ozone layer is the byproduct of a biosphere that has evolved to use oxygenic photosynthesis. And in any case, an ozone layer can only exist on a planet with a strong magnetic field. Otherwise it will get stripped away by the solar wind of its host star.

[Noclevername]

Would these atmospheric conditions necessarily remain stable on a biospheric world? Earth's toxic-gas period covered most of our planet's existence, but when photosynthesis came along, it changed our entire atmosphere, purged out most of the toxins (from our POV) and allowed life to adapt to free oxygen and develop complexity.

Couldn't an exoplanet be capable of the same process?

[iancampbell]

Would these atmospheric conditions necessarily remain stable on a biospheric world? Earth's toxic-gas period covered most of our planet's existence, but when photosynthesis came along, it changed our entire atmosphere, purged out most of the toxins (from our POV) and allowed life to adapt to free oxygen and develop complexity.

Couldn't an exoplanet be capable of the same process?

 Possibly. But there are IMHO two problems with this. One is that the resulting biosphere might generate minor amounts of gases that would be dangerous to Earthly life (the OP mentioned Earthly animals) such as chlorine, ammonia or CO.

The other is that a planet like Earth might be quite rare, in particular the fast spin which largely generates the magnetic field that protects our atmosphere from the solar wind. It's seriously postulated that the rotation of proto-Earth was quite slow, until the Thera event that spun Earth up and created the Moon. After all, of the terrestrial planets only two have reasonably fast spin. And the magnetic fields of Mercury and Venus are negligible. Venus in particular, which is virtually a twin of Earth in most respects, has almost no magnetic field - because it has a rotation period approximately equal to its year.

[Avalancheon]

Possibly. But there are IMHO two problems with this. One is that the resulting biosphere might generate minor amounts of gases that would be dangerous to Earthly life (the OP mentioned Earthly animals) such as chlorine, ammonia or CO.

The other is that a planet like Earth might be quite rare, in particular the fast spin which largely generates the magnetic field that protects our atmosphere from the solar wind. It's seriously postulated that the rotation of proto-Earth was quite slow, until the Thera event that spun Earth up and created the Moon. After all, of the terrestrial planets only two have reasonably fast spin. And the magnetic fields of Mercury and Venus are negligible. Venus in particular, which is virtually a twin of Earth in most respects, has almost no magnetic field - because it has a rotation period approximately equal to its year.

Just a minor nitpick. A distinction should be drawn between the rotation of the Earth itself, and the rotation of its core. They are strongly related, but not identical... After all, it is known that the inner and outer core rotate in different directions. They are ultimately the source of the Earths magnetic field.

The Earths core is able to rotate in this manner because it is still hot enough to remain liquid. The core of Mars lost too much heat and froze solid eons ago. Like you say, our planets superheated core may be tied to the Theia impact which formed the Earth and Moon.