Ultraviolet-bright M dwarfs, oxygen-rich planets?

[Ann]

Astronomers are of course eagerly looking for signs of life on any of the many exoplanets that have been discovered in recent years. Planets orbiting inside the habitable zone of M dwarfs are considered particularly interesting, because M dwarfs are so abundant and because their rather low mass and feeble light make it comparatively easy to detect planets orbiting them.

An oxygen-rich atmosphere has been considered a sure sign of life, due to the fact that high concentrations of free oxygen can't exist in nature unless there is some sort of process replenishing the oxygen. Here on Earth, free oxygen is byproduct of photosynthesis of plants, and it is therefore "made" by biological life. Therefore, if a planet orbiting an M dwarf could be shown to have an oxygen-rich atmosphere, that might be seen as a sure sign of life on that planet.

But Feng Tian (National Astronomical Observatories of China) and four colleagues from the U.S. and Argentina, point out that M dwarfs often produce as much far ultraviolet light as the Sun, but at the same time they produce very little near ultraviolet light. Tian and colleagues point out that all that far ultraviolet light could break up CO2 in a planet's atmosphere and lead to the formation of O2 and O3. The shortage of near ultraviolet photons would prevent the re-formation of CO2. As a result, O2 and O3 would build up in the planet's atmosphere, mimicking an atmosphere which is oxygen-rich due to biological life.

Read more here.

Ann

[Beyond]

Geeze, there's always a 'catch' to everything.

[BDanielMayfield]

Glad you posted this interesting comment Ann. Since we’re O2 breathers I think this is great news, irregardless of the difficulties it may pose for the search for ET. Perhaps this means that some planets of red dwarf stars come equipped with ready made UV atmospheric shields comparable to Earth’s ozone layer, which could be very handy on a planet up close to a flaring red dwarf star.

On an amusing side point, I couldn’t help but notice your use of the phase “biological life”. Is there any other kind, prey tell?

[Chris Peterson]

On an amusing side point, I couldn’t help but notice your use of the phase “biological life”. Is there any other kind, prey tell?

There certainly is in theory, and perhaps before too much longer, in practice. And of course, there may be non-organic life, which is what I think might be called non-biological in some contexts.

[BDanielMayfield]

On an amusing side point, I couldn’t help but notice your use of the phase “biological life”. Is there any other kind, prey tell?

There certainly is in theory, and perhaps before too much longer, in practice. And of course, there may be non-organic life, which is what I think might be called non-biological in some contexts.

You must be referring to engineered, robotic “life” in the first case. By your use of “non-organic” do you just mean not carbon based, or something else?

[Chris Peterson]

You must be referring to engineered, robotic “life” in the first case.

Engineered or artificial. Not necessarily robotic. (I believe that the first artificial life will exist entirely within a computer of some sort.)

By your use of “non-organic” do you just mean not carbon based, or something else?

I just mean not carbon based.

[BDanielMayfield]

You must be referring to engineered, robotic “life” in the first case.

Engineered or artificial. Not necessarily robotic. (I believe that the first artificial life will exist entirely within a computer of some sort.)

By your use of “non-organic” do you just mean not carbon based, or something else?

I just mean not carbon based.

Right. This really gets into what it means for something to be alive, doesn’t it?

In works of science fiction self replicating machines are a recurring theme. Nice concept if it can be pulled off, provided that it can be controlled of course. The capacity life has for exponential growth makes it extremely powerful. It’s a long shot, but some day planets might be teraformed with the help of such technology.