Alien Life Hunt: Oxygen Isn't the Only Possible Sign of Life

[Judi Lynn]

By Mike Wall, Space.com Senior Writer | January 27, 2018 08:24am ET

Alien-life hunters should keep an open mind when scanning the atmospheres of exoplanets, a new study stresses.

The time-honored strategy of looking for oxygen is indeed a good one, study team members said; after all, it's tough for this gas to build up in a planet's atmosphere if life isn't there churning it out.

"But we don't want to put all our eggs in one basket," study lead author Joshua Krissansen-Totton, a doctoral student in Earth and space sciences at the University of Washington in Seattle, said in a statement. [5 Bold Claims of Alien Life]

"Even if life is common in the cosmos, we have no idea if it will be life that makes oxygen," Krissansen-Totton added. "The biochemistry of oxygen production is very complex and could be quite rare."

More:
https://www.livescience.com/61540-alien-life-biosignature-gases-oxygen.html?utm_source=notification

[NNadir]

1. Oxygen was not a feature of life on this planet for a significant period in its history.

In fact when photosynthetic organisms first evolved, their waste, oxygen, ended up killing a huge fraction of the living organisms on the planet.

Many life forms still thrive here without oxygen.

If people have been looking for oxygen to show the presence of life - and I'm pretty sure they haven't been so limited - they're going to miss a lot.

One would miss a lot of life on this planet if one insisted oxygen must be present.

[struggle4progress]

3. They suggest looking for CO2 and CH4 present but with little CO

[NNadir]

4. If one refers to the original paper which is linked in this news article and is open sourced...

...one can see that this not exactly true.

The paper is actually a thermodynamic argument - quite a good one actually - which says that the signature of life should be disequilibrium, that is a metastable state ruled by kinetics rather than by free energy.

I once had a remarkable afternoon sitting with Freeman Dyson, my two sons and my youngest son's best friend, and somehow the subject of Stuart Kaufman came up and I offered to Dyson Kauffman's definition of life as being "an eddy in thermodynamics."

It turned out that Dyson - who seemed to know everything all at once despite being in his late 80's when I met him - knew Kauffman personally, but he remarked that this was, in fact, an excellent definition of what life is.

I agree.

Methane is one of the most common compounds in the universe; CO2, another. In combination they are subject to the Boudouard equilibrium, actually something quite like it, and CO is an equilibrium component of the system, in the presence of a catalyst.

The toxic nature of CO to mammals is a function of mammalian oxygen transport by heme and its equilibrium between oxygen and carbon dioxide, which relies on the poor stability of either complex. The CO complex by contrast is extremely stable, as is iron carbonyl; this is also true of the isoelectronic ion cyanide, which forms the extremely stable prussic acid and the cyanide salt one can actually eat as an antidote to certain syndromes, prussian blue, ferroferricyanide..

There is no intrinsic reason that CO should be toxic to all life forms, any more than cyanide is. It seems possible that the cyano ion in particular is or was essential to the generation of life.

However a system at a particular temperature in which there was both carbon dioxide and methane but no carbon monoxide would be in disequilbrium, at least if was old.

But it is possible at certain temperatures, the system would be metastable and in kinetically driven disequilibrium, as indeed the earth is, since, for one example, there is atmospheric methane in the presence of oxygen. (The authors claim that nitrogen, water and oxygen mixtures are metastable and should form nitric acid. I'm too lazy to check this calculation myself, but it's the first time I heard that one.)

Wood of course, is not stable in the presence of oxygen. This is why it burns. It exists because the activation energy is high. But an oxygen containing atmosphere containing wood but where wood was not regenerated by living organisms, would ultimately reach equilibrium where no wood would exist. It is thus in disequilibrium.

We are only just very barely able to understand - at a very low level - the chemistry of exoplanets. It's not going to be easy to get a good picture of exoplanet chemistry, so this point may be moot for some time to come.

[struggle4progress]

5. "... simultaneous detection of abundant CH4 and CO2 .. is a potential biosignature ...

Biogenicity would be strengthened by the absence of abundant CO, which should not coexist in a biological scenario ..."

http://advances.sciencemag.org/content/4/1/eaao5747

[NNadir]

6. Strengthened, not proved, particularly in an alien system using poor resolution.

I read the article, and - at least in my own mind summarized it and offered some objections to the statement.

We live on a planet with a disequilibrium with respect to methane, some of which is a product of our industrial system and some of which is biotic.

I very much doubt that a sophisticated civilization living only a few parsecs away perhaps could detect the concentrations of methane on our planet, which is very much a signature of life.

The paper is still highly speculative, far more so than authoritative.

[SCantiGOP]

2. I have also read

explanations about how life could be other than Carbon-based, such as based instead on silicon, and would not necessarily be dependent on oxygen.