Thanks to data from ESA’s Rosetta, astronomers have estimated that 40 percent of the nucleus of Comet 67P/Churyumov-Gerasimenko is made of organic materials. Two French researchers have now proposed that this organic material formed long before the Solar System.

According to Jean-Loup Bertaux and Rosine Lallement, the organic material of 67P was formed in interstellar space, in the so-called diffuse interstellar bands (DIBs). It has been known for seven decades that organic material exists in the space between stars, and scientists have considered DIBs the largest reservoir of complex prebiotic molecules in the universe.

DIBs were discovered because they selectively absorb certain wavelengths of light. These features can be seen all over the galaxy but tend to be less significant around protostellar nebulae. This has been a key factor in the researchers’ hypothesis.

The reason DIBs' absorption dips in nebulae is that material is clumping together and that clumped material absorbs less light. The data from Rosetta showed that the comet formed from the gradual accretion of bigger and bigger grains. Eventually becoming comet sized.   

These organic molecules are made of carbon, hydrogen, nitrogen, and oxygen and they also play a role in the formation of planets. But while in planets they interact with other elements and change, the researchers believed that they would be unaltered inside the core of a comet.

“This conclusion implies that a future sample-return mission of a comet nucleus would not only provide unique information on comets, but also on the exact nature of the interstellar species producing the hundreds of DIBs, an unanswered question since their discovery several decades ago,” the researchers wrote in the paper, which is published in the Monthly Notices of the Royal Astronomical Society.

Understanding the nature of DIBs could have far-reaching consequences. These mysterious molecules are so common throughout the galaxy, so they might be playing a role in the potential emergence of life outside Earth.

Confirming DIB molecules in comets might also expand on the emergence of life on Earth. Scientists think comets brought complex molecules to our planet and a thorough analysis might prove that to actually be the case.