Mikko Tuomi

Here is a problem that has been quietly gnawing at astronomers for decades.

The standard approach to detecting #life on other worlds involves scanning #exoplanet #atmospheres for #oxygen, #methane, and #ozone, whose presence is difficult to explain without #biology.

It's a clever idea, but it carries a hidden flaw. That entire shopping list was written by studying Earth. It is, inevitably, a search for life like us.

The list of ways that #chemistry alone can accidentally mimic these #biosignature gases is growing faster than the list of new ways to detect life.

Each new false positive scenario demands even more information about the #planet to rule it out, and there is a genuine question about whether that information can ever be gathered exhaustively.

But there is a solution.

#Assembly theory doesn't ask what #molecules are present in an #atmosphere. Instead, it asks how hard they were to make.

Every molecule can be assigned an assembly index, a minimum number of construction steps required to build it from basic #chemical building blocks.

Simple molecules are easy to assemble by chance, but truly complex ones, requiring many sequential steps, don't arise without something doing a great deal of deliberate selection.

That something would then be life itself.

#astrobiology #astronomy
https://phys.org/news/2026-03-life.html

Paper by Walker et al. (2026): https://arxiv.org/abs/2603.11086

Life, but not as we know it

Here is a problem that has been quietly gnawing at astronomers for decades. The standard approach to detecting life on other worlds involves scanning exoplanet atmospheres for oxygen, methane, and ozone, whose presence is difficult to explain without biology. It's a clever idea, but it carries a hidden flaw. That entire shopping list was written by studying Earth. It is, inevitably, a search for life like us.

Phys.org
Mar 19 at 11:09pmWeb
Show threadZalasur 🐸🇺🇦Mar 20

@mustapipa The main problem with that approach is that those complex molecules are very hard to detect with spectroscopy, our only method of detecting chemicals on other planets. The more complex the molecule, the more "muddied" the spectral lines.

Looking for the basic molecules is a way of narrowing down the list of potential planets that we can than look at in more detail for other non-chemical signatures.

Show threadMikko TuomiMar 20
@zalasur Of course, but things can be learned without comprehensive solutions, too. Perhaps we only have to learn to live with uncertainty.
Show threadBen HourahineApr 15
@zalasur @mustapipa @zalasur @mustapipa the bigger problem is assembly theory itself, which is considered junk science in a number of quarters: How complex a structure currently is says very little about how it came to be like that. 1) specific to chemistry, the landscape of barriers between precursors in the synthesis, and precursor availabilities, is what determines what you get (it's the journey that matters). 2) more generally, from what we know about non-linear processes (c.f. chaos theory), complex patterns can and do emerge from simple components or rules spontaneously (in a chemistry context, things like the Belousov-Zhabotinsky reaction, while not synthesis, shows this). 3) if assembly theory (edited for typo) is right, how would abiogenesis work?
Show threadMikko TuomiApr 15

@BenHourahine @zalasur I think there is a bit of a distraction based on rhe word "theory".

This is simply an effort to measure how complex is the complexity required for life. The mechanisms regarding the formation are somewhat beyond the scope in that respective, even though very much related.

Show threadBen HourahineApr 15
@mustapipa @zalasur so that would be point 3. Regarding the first two, taking a static snapshot of something complex isn't too informative.
Show threadMikko TuomiApr 15
@BenHourahine @zalasur Perjaps, but a static snapshot is pretty much all we get looking at habitable exoplanets, and whether they have been infected by life.
Show threadWelkinMar 20
@mustapipa
In a universe which is 13+ billion years old and more than 90+ billion light years across the chance of building such complex molecules without life playing a part is a real possibility if not a forgone conclusion.
I agree that life, like we know of, may not be the only possible outcome. Life may be silica based instead like us, which is carbon based.
Show threadMikko TuomiMar 22

@welkin7 Silicon has been proposed, but it doesn't have anywhere near the chemical complexity and possibilities that carbon provides. It simply seems very improbable as a building blocks of life.

Same applies to water as a solvent. There really are no credible substitutes for carbon-based molecules dissolved in water as a basis of life.

Show threadKevin MorganApr 15
@mustapipa Sounds familiar. Like another version of Kolmogorov complexity.
Show threadMikko TuomiApr 15
@Jvmguy I guess those could be related, not sure about the details.