When astronomers search the skies for signs of alien life, they tend to focus on planets that are relatively similar to Earth. But while looking for the kinds of life we know exist is a good place to start, different conditions on different planets could have led life down paths that are completely … well, alien. To demonstrate, a NASA-funded study has successfully created a new synthetic genetic system that's a viable alternative to DNA, made with twice as many "ingredients."
All life on Earth is made up of DNA molecules, and those in turn are composed of four nucleotides: adenine, thymine, cytosine and guanine (A,T C and G). All information about an organism, from bacteria to blue whales, is encoded in sequences of repeating pairs of these four bases.
But just because DNA is common to every creature on Earth doesn't mean it's the only way life can arise. After all, every form of life on this planet – past, present and future – shares a common ancestor if you trace it back far enough. On other worlds, life could have started with a completely different structure.
Researchers from the Foundation for Applied Molecular Evolution, the University of Texas, Indiana University Medical School and DNA Software set out to test what kinds of alternatives might be viable.
The team managed to create a new molecular system that functions the same way as DNA, and is stable enough to store and transmit information. Along with the four familiar nucleotides, the new synthetic DNA molecule contains four brand new ones. The system has now been named "hachimoji" DNA, which is Japanese for "eight letter."
While it's pretty unlikely that any aliens out there are using this exact system, the research goes to show that our tried-and-true DNA isn't the only possible structure for life. In practical terms, that means that astronomers searching for extraterrestrial life could be missing out by focusing on Earth-like worlds.
"By carefully analyzing the roles of shape, size and structure in hachimoji DNA, this work expands our understanding of the types of molecules that might store information in extraterrestrial life on alien worlds," says Steven Benner, lead researcher on the study.
Hachimoji isn't the first time scientists have toyed with synthetic DNA. In 2010, a team created a synthetic bacterial cell that ran on a computer-designed genome and could self-replicate. In 2017 other researchers added two new bases into the genome of E. coli to make a semi-synthetic organism, and a few months later it produced a completely unknown protein.
Along with potentially aiding our search for alien life, the team says that the Hachimoji system could also be used as a base for more of these kinds of synthetic biology experiments.
The research was published in the journal Science.
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