DNA from Space? Nucleobases from Ryugu and the origin of life

Let's take a break from going on and on about hominin fossils and talk a little biochemistry instead. I'm seeing (once again) big headlines talking about how five of the essential ingredients of life were found on asteroid Ryugu. I'm actually kind of impressed this time, since most of the headlines are actually pretty tame, except for a few headlines claiming "all the ingredients" for DNA or life have been found. Still, these sorts of discoveries get spun into some kind of support for models of the abiotic origin of life, that is, life spontaneously emerging from dead chemicals. As a biochemist by training, I got some strong opinions about that, so let's take a look.

The Hayabusa 2 mission, run by the Japanese space agency JAXA, rendezvoused with an asteroid called 162173 Ryugu in the summer of 2018, after 42 months of travel from earth. Hayabusa 2 spent seventeen months observing the asteroid, then collected samples from the surface. Those samples arrived on earth successfully on December 5, 2020, which honestly is a pretty tremendous technical achievement.

Now, researchers report finding parts of DNA and RNA in the samples, specifically all five canonical bases. If it's been a while since high school biology, the bases of DNA are the parts in the middle that stick together to make the double strand. There are four of them in DNA, guanine, adenine, cytosine, and thymine. In the related molecule RNA, which is also found in all cells on earth, thymine is replaced with a similar base called uracil. That's five bases in all, but they need additional sugars and phosphates to make up the backbone of the nucleic acid. Those components must be attached in the correct way, which is not guaranteed, in order to make DNA or RNA. Also, you have to make sure there's only thymine in DNA and uracil in RNA. How much of each? Well, the human genome is said to have three billion of these bases, but in DNA they come in pairs, so it's six billion. And human cells are diploid, with two copies of every chromosome, so it's twelve billion bases for a human genome. For a bacterial genome, you might need four million bases, give or take a million. Either way you go, that's a lot of bases.

These findings are not that surprising, since we've known since 1961 that adenine at least could be generated using hydrogen cyanide and ammonia. Scientists have also found bases in other asteroids and meteorites. Not surprisingly, the concentration of bases from these sources is correlated with the concentration of ammonia. Does this really tell us about the origin of life?

To be quite blunt: No. As I said, we've known for 60+ years that DNA bases could be synthesized with some very simple chemistry. The bases contain just carbon, oxygen, hydrogen, and nitrogen. Nothing particularly unusual. Since we've known so long that these components could be generated, there's not much new in the Hayabusa 2 results except confirming what we already knew in yet another asteroid.

More importantly, these are some of the simplest biochemicals that make up living things. As I said, there are millions or billions of these in each cell, and they form linear arrays carrying information in the sequence of the bases. That information is effectively independent of the chemistry of the bases themselves. For example, the DNA bases guanine - thymine - cytosine are equivalent to the RNA bases guanine - uracil - cytosine and through the process translation the information in that chemical sequence codes for valine. As far as we know, there's nothing about the chemistry of any of these things that would necessitate that sequence to code for valine. It just does.

By analogy, imagine discovering a trove of letters on an asteroid and imagining that that trove somehow explained the origin of Romeo and Juliet by natural processes. I don't think you'd be convinced.

At the same time, I think there's something quite remarkable here that the design of life utilizes these easily made chemicals. That goes also for amino acids and sugars and a host of other biochemicals that really can be made with simple chemical reactions. It's almost as if chemistry was designed to serve the greater good of making life possible. Maybe I should say more about that in the future somewhere, maybe in a book or something.

Maybe later.

As always, don't take my word for it. Check out the original research article. It's open access!

Koga et al. 2026. A complete set of canonical nucleobases in the carbonaceous asteroid (162173) Ryugu. Nature Astronomy 10.1038/s41550-026-02791-z. 

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Have you read my book?  You should check that out too!