Two prebiotic molecules - one related to DNA and the other to an amino acid - have been identified in a gas cloud near the center of the Milky Way.
The discovery indicates that some basic chemicals that are key steps on the way to life may have formed on dusty ice grains floating between the stars.
"Finding these molecules in an interstellar gas cloud means that important building blocks for DNA and amino acids can 'seed' newly-formed planets with the chemical precursors for life," says Anthony Remijan, of the National Radio Astronomy Observatory (NRAO).
Using the National Science Foundation's Green Bank Telescope (GBT) in West Virginia, the team examined a giant gas cloud some 25,000 light-years from Earth - and discovered a molecule thought to be a precursor to a key component of DNA and another that may be involved in the formation of alanine.
Both molecules are intermediate stages in multi-step chemical processes leading to the final biological molecule. Cyanomethanimine is a step in the process that chemists believe produces adenine, one of the four nucleobases that form the 'rungs' in the ladder-like structure of DNA. Ethanamine, meanwhile, is thought to play a role in forming alanine, one of the twenty amino acids in the genetic code.
Previously, scientists thought such processes took place in the very tenuous gas between the stars. The new discoveries, however, suggest that the chemical formation sequences for these molecules occurred not in gas, but on the surfaces of ice grains in interstellar space.
"We need to do further experiments to better understand how these reactions work, but it could be that some of the first key steps toward biological chemicals occurred on tiny ice grains," says Remijan.