When astrophysicists look at exoplanets, they’re not looking for life as such, as life is impossible to detect at a distance of light years. What they’re looking for is an unbalanced equation.
Think about rust. What is rust? It’s iron oxide. The chemical equation for your rusting pickup truck is…
This is a balanced equation.
Put oxygen, iron and water together and you’ll get rust. Understanding this, we can look at a planet like Mars and see rust on the surface and realize there must have been oxygen and water in abundance there in the past as that chemical equation has balanced itself.
If an alien civilization looked at Earth, they would see an unbalanced chemical equation in our atmosphere. They’d see lots of oxygen and trace amounts of methane. But that isn’t possible. The oxygen and methane in our atmosphere should have reacted just like oxygen, water and iron react to form rust. Oxygen and methane combine to form carbon dioxide and water. That this hasn’t happened would tell them that there’s something changing the equation—and that something is life! Life keeps producing methane faster than it can be converted into CO2 and water. These hypothetical aliens would be able to look at Earth and say, “Well, there must be life there or with that much oxygen in the atmosphere, we’d never see any methane.” And they’d be right.
Measuring chemical compounds in the atmosphere of a planet orbiting another star at a distance of a hundred light years is akin to detecting the polysaccharide in a mosquito’s wings as it flies in front of a spotlight at a football game. It’s an astonishing achievement in its own right and allows us to sample the atmosphere of planets we’ll probably never visit, ever.
Recently, the James Webb Space Telescope detected dimethyl sulfide and dimethyl disulfide in the atmosphere of a gas giant orbiting a red dwarf star 124 light years from Earth, but what does this mean? How could this reveal the presence of alien life?
Dimethyl sulfide (CH3)2S gives us the smell of cooked cabbage, while dimethyl disulfide CH3SSCH3 smells like garlic. On the surface, we’re getting a hint of Masterchef: Red Dwarf Edition.
Seriously, though, these compounds have been detected with a three-sigma level of confidence in the measuring process. In a normal distribution (bell curve), 68% of values fall within ±1σ, 95% fall within ±2σ, and 99.7% fall within ±3σ, so the chances of this detection being a mistake is a mere 0.3%.
The question then becomes—what could produce these compounds? Could they be made by natural processes or are they the result of life?
Dimethyl sulfide has been found on comets, so it can be produced by processes other than life.
Here on Earth, dimethyl disulfide is produced by marine phytoplankton, so it’s a really good candidate for evidence of life.
The question then becomes what other processes produce dimethyl sulfide and dimethyl disulfide in quantities similar to what we see on the planet K2-18 b in the constellation of Leo?
Prof Nikku Madhusudhan, an astrophysicist at the University of Cambridge, said, “I don’t think there is any known process that can explain this without biology.”
So… have we found life elsewhere in the universe? Maybe.
For now, the question shifts to looking for other natural mechanisms for producing these chemical compounds, but it may be that the natural mechanism is life itself.
The planet K2-18 b will be the focus of further studies as we seek to understand the origins of this unusual, unbalanced equation.
