View Full Version : methanogen

John Kierein
2002-Jan-17, 12:29 PM
I think I'm getting gas from these guys.

2002-Jan-17, 02:05 PM
The Viking biological experiments on Mars were originally thought to show signs of life, but the results were discounted when a chemical experiment showed no signs of organics. Now this finding shows that life can exist without what are thought of as organic (carbon-based) chemicals. Is it time to revisit the Viking results?

2002-Jan-18, 04:18 AM
That's a rather serious misunderstanding of that finding.

What was discovered was an underground ecosystem whose primary producers are methanogens. These are a kind of bacterium that have long been known; they live off of this chemical reaction:

CO2 + 4*H2 -> CH4 + 2*H2O

This is exothermic, that is, energy-releasing, and this explains why methanogens do not need to live off of either organic compounds or light. Methanogens also perform all the biosynthesis they need, just as plants do.

The extraterrestrial-life connection is that other places in the Solar System may offer places congenial to methanogen-based communities; this would be the case if they have both carbon dioxide and hydrogen gas.

Mars has carbon dioxide, but any hydrogen gas would have to be outgassed from the interior, as also happens on Earth. But Earth outgassing is related to its geological activity; Mars is essentially dead geologically, with no evidence of volcanic eruptions or tectonic activity in geologically recent times.

Europa I'm not sure about; I'm not sure how much of either carbon dioxide or hydrogen can reasonably be expected in its interior. But Europa is geologically active, with its surface being relatively young by geological standards, as evident from its paucity of craters. And this geological activity may mean some releasing of hydrogen and/or carbon dioxide into its ocean, and thus possible methanogen-based communities.

Europa's heating comes from an unusual source. Jupiter's satellites perturb each other, creating a bit of eccentricity in their motions; this means that they will experience varying strength of Jovian tide. This flexes the moons, heating them; Io is heated especially strongly by this effect, and Europa is heated enough to have a liquid ocean, though one that is iced over.

I don't expect much of present-day Martian life, except if some hot spring is discovered somewhere on it.

However, Europan life offers more possibilities. If its methanogens are sufficiently productive, they can sustain a large community of Europan life. But this community would be limited to fermentation, since there would be no oxygen available for highly energetic metabolism. So there may not be much more than microbes, with no full-scale animal life like Europan tube worms.

2002-Jan-18, 01:48 PM
Thanks for the clarification.

2002-Jan-20, 10:03 AM
The problem with the Viking results is that they show:

1. The Martian soil has the ability to "eat" the prebiotic broth used, releasing CO and/or CO2.

2. The Martian soil has no sign of organic compounds.

The explanation that is most consistent with these results and what Mars's surface is like is that the Martian soil has an abundance of peroxides and superoxides -- and no organic compounds.

Those peroxides and superoxides are produced by solar ultraviolet reacting with adsorbed water and water ice; this ultraviolet also destroys most organic compounds, leaving an insoluble tar -- at best.

And they react with the organic materials in the broth, producing CO and CO2 and perhaps other carbon-containing gases like methanol vapor. These reactions are helped by both the illumination in the experimental chamber and the catalytic properties of the exposed minerals in the soil.

So Mars's topsoil is most likely sterile, though Martian hot springs, if they exist, may have Martian life in them.

John Kierein
2002-Jan-23, 09:19 PM
More. This time on Europa.