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

Organic #molecules delivered from #extraterrestrial materials may have played a key role in supplying building blocks for #life on #Earth.

Now scientists report all five canonical #nucleobases—purines (#adenine and #guanine) and pyrimidines (#cytosine, #thymine and #uracil)—in samples returned from the C-type #asteroid (162173) #Ryugu.

Samples from Ryugu, #Bennu and #Orgueil, which have a similar mineralogy and elemental composition, show purine-to-pyrimidine ratios negatively correlating with #ammonia.

These observations indicate that the nucleobases in these samples may have formed via a shared pathway depending on the physicochemical environment of the respective parent bodies.

The detection of diverse nucleobases in asteroid and meteorite materials demonstrates their widespread presence throughout the Solar System and reinforces the hypothesis that carbonaceous asteroids contributed to the #prebiotic chemical inventory of early Earth.

#astronomy #astrobiology
https://www.nature.com/articles/s41550-026-02791-z

"n a study published in Nature Astronomy today, a team of Japanese scientists has confirmed all five nucleobases are present in this pristine asteroid [Ryugu] material.

This means these ingredients for life may have been widespread throughout the Solar System in its early years."

https://theconversation.com/all-5-fundamental-units-of-lifes-genetic-code-were-just-discovered-in-an-asteroid-sample-278099

#Asteroids #Ryugu #Samples #Molecules #Nucleobases

🔄 Tiny, 45 base long RNA can make copies of itself

https://arstechnica.com/science/2026/02/researchers-find-small-rnas-that-can-make-copies-of-themselves/

#rna #molecules #replication #molbio