We pretty much have evidence for life in other solar systems
[This is a transcript with links to references.]
Scientists have found tentative evidence for life in another solar system. There’s been headlines like this for a couple of years now, the most recent ones come from data from the James Webb Space Telescope and a planet called K2-18b. Today I want to have a look at what we know about life on this and other exoplanets. And why I think astrophysicists have pretty much found life on other planets, it’s just that they’re not yet allowed to say it.
When astrophysicists talk about life on other planets they mean “biosignatures” that is some sort of evidence that life in a form we know of might be present. They look for this by scanning the atmosphere of these planets for certain molecules, or combinations of molecules, that at least on earth signal the presence of life.
Biosignatures would be evidence for life, but not necessarily for complex life. To tell the two apart, astrophysicists also look for technosignatures, that would be signs of any sort of technology indicating intelligent beings. But it’s a very crude distinction in that there is a lot that can happen between microbes and air pollution so severe you can literally spot it from lightyears away.
The key biosignatures they look for are molecular combinations that should not exist in chemical equilibrium, because there are no geological processes that produce them, at least none that we know of.
That said, let us look at the headline cases. The most intensively discussed potential detection is K2 18b. This planet is a little larger than earth in a solar system about 124 light years away. It sits in the habitable zone of a red dwarf. Already in 2019, the Hubble telescope detected water vapor in its atmosphere. That’s not a biosignature on its own but it’s… suggestive.
In 2023, an analysis of preliminary data from the james webb space telescope reported methane and carbon dioxide. But then, last year, the same team returned with better data and reported a 3-sigma detection of dimethyl sulfide at concentrations that seem to be thousands of times higher than on earth. On earth, this is gas produced on Earth almost exclusively by marine microbes. They called it the strongest evidence yet of possible biosignature activity outside the solar system.
Alas, reanalyses by independent groups found that the data was consistent with many other possible chemical compositions and basically inconclusive.
There have been other planets of interest, for example TOI-270 d. This planet too is a little larger than earth and orbits around a dwarf star about 73 light years away from us. However it is rather close to the star which puts it at the edge of the habitable zone. For this planet, the data is much better: twoindependent groups have found reasonably strong signature of methane, carbon dioxide, as well as carbon disulfide and ethane. Again, on earth these are produced by microorganisms. However, in this case one can’t rule out that there are other, non-biological sources. So the data is also inconclusive, though for a different reason.
There are many more planets that have attracted interest in the past years, but where the data has remained inconclusive for one reason for another. For example the Trappist system that is only 40 light years away from us. Its sun is a red dwarf, only slightly bigger than planet Jupiter, but it has at least 7 rocky planets, 3 of which seem to be in the habitable zone. So if the system is that much closer to us and that much more promising, then why don’t astrophysicists just look at those.
It’s because the red dwarf is so small and yet very active. That it’s so small means that the habitable zone is very close to the star, and that it’s so active makes it very difficult to find out whether the planets there even have an atmosphere. Astrophysicists have looked at this over and over but not been able to get any good data. They have now scheduled more than a dozen additional observation runs with the James Webb space telescope, so maybe we will soon know more.
There are more than these example planets that astrophysicists have found in habitable zones, some look promising, some not so much. The sense I get is that it’s only a matter of time until they will find a candidate that checks all boxes and the significance for the biosignatures is high enough. You can basically see it coming.
I have reason to believe I am not the only one who thinks this way. The other day I came on this comment on X/twitter “Was speaking to an academic astrophysicist in spectroscopy who told me that they have so many plausible exoplanetary atmospheric biosignatures at this point that there’s no longer any real doubt, but the standard of proof for official acceptance is just incredibly high.”
This is exactly my impression as well. Then again some in the field have recently claimed that with the James Webb Telescope we will never be able to reach the required significance to declare have evidence for life on an exoplanet. Maybe they’re right. But I think it’s just an excuse to ask for a bigger telescope. Not necessarily a bad one.
Evidence for Life In Other Solar Systems? No but yes. (YouTube)
Comments (10)
Happy to discover here. Your interests including even your healthy critical analytic perspective feels immediately refreshing and resonant.
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thanks for your support and for sharing this story! very interesting
I think the much more interesting question is mother earth sentient or even every point of existence sentient. I think only evolution can make things better, so a highly intelligent existence next to us would only interfere if something catostrophic to all life were to occur. Otherwise evolution and noninterference would be happening all the time.
What does three- or six-sigma mean in this context? Across all stars of a given type? “Let’s keep searching till we find the data point that supports our hypothesis” is not good statistics.
Distinction Theory explains the Fermi paradox this way: as civilizations become more complex, they are harder to keep stable, so most collapse before they last very long. The few that do survive reduce their energy use and avoid sending out strong signals in order to stay stable, which makes them very hard to detect. As a result, even if intelligent life is common, long lived and detectable civilizations are rare. In this framework, humanity is still operating at Recursive Distinction Depth 2, meaning we can model the world but not fully stabilize or correct our own behavior, which puts us in the unstable phase where collapse risk is highest before reaching a truly stable, self-correcting state.
I am not convinced that no nonliving process can produce those compounds. But I don't know my organic chemistry well enough to be sure. I passed with only a C+ 25 years ago.
that's a pretty good grade for OChem! 😆
With the latest estimates to be approximately two TRILLION galaxies in the known Universe, with hundreds of billions of stars in each one, the chances of life in the universe other than earth are just phenomenal. It is almost 100% guaranteed that we are not alone- and given the age of the Universe, the chances of intelligent life is extremely high- but because of the distances and the prohibition of light speed, we are probably not going to find out anytime soon, unless governments level with us about alien life visiting earth, or we find a way of defying the E=MC2 constant.
The Habitable Worlds Observatory (HWO), which is expected in the late 2030s or early 2040s, is designed to detect and characterize Earth-like exoplanets. Extraordinary claims require extraordinary evidence and extraordinary telescopes, in this case. If we find life or fossils in Mars or in the oceans of any Moons in the Solar System, or in asteroid samples, then life could be everywhere and anywhere. Something incredible may just be waiting to be discovered. Keep searching. We are spending far more in just pets care.