Has NASA Found a Second Genesis?

By Robert Zubrin

Thursday, September 14, 2023

 

On September 11, an international team of astronomers led by Cambridge University professor Nikku Madhusudhan announced that, using NASA’s James Webb Space Telescope, they had found potential evidence of life in the atmosphere of another world.

 

The planet in question, known as K2-18b, orbits in the habitable zone — the “Goldilocks region,” where temperatures are neither too hot nor too cold for liquid water — of K2-18, a K-type red dwarf star located in the constellation Leo some 110 light-years from Earth. K2-18b is 8.6 times as massive as the Earth, intermediate in size between Earth and Neptune. Such “sub-Neptune” worlds are among the most common types of exoplanets detected around other stars, but K2-18b might also be a hycean (a portmanteau of “hydrogen” and “ocean,” coined by Madhusudhan and others in a 2021 paper), as its surface appears to consist largely or entirely of liquid water.

 

Those two facts would make K2-18b interesting enough, but what is really exciting is the composition of its atmosphere. According to the data presented by Madhusudhan’s group, K2-18b’s air appears to consist mainly of hydrogen, but it also contains smaller amounts of methane and carbon dioxide and possibly trace amounts of dimethyl sulfide.

 

On Earth, dimethyl sulfide is only found as an artifact of microbial metabolism. Therefore, it is considered to be a biomarker — evidence of the presence of life. Unfortunately, the K2-18b dimethyl sulfide detection data is not yet conclusive.

 

However, while it has attracted less attention so far, in my view the positive detection of substantial amounts of CO₂ and methane in a hydrogen-dominated atmosphere really does make a powerful case that there’s life on K2-18b. This is because CO₂ readily reacts with hydrogen to produce methane and water.

 

The chemical equation for this reaction is: CO₂ + 4H₂ → CH₄ + 2H₂O

 

I am very familiar with this reaction, which is also known as the Sabatier reaction, because it is the basis for the chemical synthesis that I proposed in 1990 for making methane rocket propellant on Mars, and which I and others have demonstrated in the lab in a large variety of systems since. It is a very easy reaction to perform because it is exothermic — releasing rather than requiring energy — and has an equilibrium constant of over 10 million driving it towards completion. Without getting excessively technical, what that means is that the reaction really wants to happen, and if you mix CO₂ and hydrogen in a Sabatier reactor in the proportions shown in the above equation, you can readily get 99 percent conversion of both. Moreover, if you provide an excess of hydrogen, the CO₂ will be completely consumed and its concentrations cut below levels detectable by sensitive instruments.

 

Because K2-18b’s atmosphere has a huge hydrogen excess, the laws of chemistry say it should have no CO₂. And yet it does. That means that there is something else besides chemistry happening on that planet that is actively throwing its atmosphere out of chemical equilibrium. That something could well be life.

 

In the 1970s, the famous scientist James Lovelock said that we would know that we’ve found an alien biosphere if we find a planet whose atmosphere defies the laws of chemical equilibrium. In our solar system, only Earth’s atmosphere does that, and it has only done so since Earth developed life. There was no free oxygen in Earth’s air before the appearance of life here because our planet’s early atmosphere contained a preponderance of gases that would react with oxygen. But photosynthetic plants changed that by invoking a process that actively breaks down CO₂ and water to set oxygen free. It would appear that an analogous process could well be operating on K2-18b.

 

Furthermore, since they react exothermically, the mixture of CO₂ and hydrogen in K2-18b’s air could readily provide a source of metabolic energy to suitably evolved organisms.

 

Where could the life on K2-18b have come from? K2-18b is much too far away to have gotten its life from Earth, or Earth from K2-18b. Its life, assuming there is any, either originated locally on K2-18b or was seeded from space as suggested by the theory known as panspermia, which hypothesizes that bacterial spores are flying between the stars, seeding planets as soon as they become habitable for microbes. However, K2-18b is very different from the early Earth, so even if it (and our world) had been seeded from the outside, it would likely have to have been seeded by very different types of microbes. Either way, if there is life on K2-18b, it almost certainly represents a separate, second genesis.

 

All life forms on Earth are believed to stem from a common ancestor because they share the same fundamental elemental and molecular building blocks, the same limited list of 20 amino acids, and the same DNA-RNA information system. But life from a second genesis could be entirely different. And if life can emerge from chemical reactions de novo in two separate places, it probably has in billions.

 

The universe could well prove to be far more interesting than anyone today can possibly imagine.