On Monday, a study declaring that all four DNA bases were detected on an asteroid generated widespread headlines. Yet many of those headlines dropped an important qualifier: “again.” The paper itself references similar findings as far back as 2011, and the years since have produced multiple confirmations and more thorough analyses. The new work was notable less for proving the bases exist in Ryugu than for resolving a prior puzzle: earlier investigations had missed them there even though they appear in numerous other asteroid samples.
Beyond the headlines, the study reveals some interesting details, since it may help answer a crucial question: how those bases arrived there in the first place. Better understanding that process could be key to refining our picture of how the raw ingredients for life reached Earth.
Searching for bases
Begin with a description of what the researchers observed. DNA and RNA, the two nucleic acids used by life, share a similar architecture. That includes the backbone: a chain of alternating sugars and phosphate groups chemically bonded together. While the specific sugar differs between DNA and RNA, the chain mainly differs in length; otherwise the backbone of every DNA or RNA molecule is the same.
The bases are what give nucleic acids the identity needed to carry genetic information. There are four (A, T, C, and G in DNA; A, U, C, and G in RNA), and one base is attached to each sugar in the backbone. The sequence of bases along the backbone encodes genetic information, enabling life as we know it. It’s been suggested that, before life arose, the order of bases along RNA molecules dictated the sorts of chemical reactions they could catalyze.
