On Monday, a paper announcing that all four DNA bases had been found on an asteroid sparked a lot of headlines. But many of the headlines omitted a key word needed to put the discovery in context: "again." The paper itself cited similar results dating back to 2011, and the ensuing years have seen various confirmations and more rigorous studies. The new work was less notable for showing that we had found these bases in Ryugu than for solving a previous mystery: earlier studies had failed to detect them there, despite their presence in many other asteroid samples.
Outside the headlines, though, the new work provides some interesting details, as it may answer an important question: how these bases got there in the first place. Understanding that better may be critical for getting a better picture of how the raw materials for life ended up on Earth in the first place.
Searching for bases
Let's start with a description of what the researchers found. Both DNA and RNA, the two nucleic acids used by life, share a similar structure. That includes the backbone, a chain that alternates between sugars and phosphates that are all chemically linked together. While the specific sugar differs between DNA and RNA, the chain itself varies only in length; otherwise, the backbone of every DNA or RNA molecule is identical.