Studying the composition of comets has allowed us to better understand the composition of the early Solar System, but it appears that there’s a lot more we need to understand about these fascinating objects.

An international team of researchers looked at 30 comets over 16 years and discovered that although they all had different substances, certain chemicals in comets only appear together with certain other chemicals and not others.

“This relates to how the chemicals are stored together or sequestered in the nucleus, or body of the comet,” said the paper’s lead author, Neil Dello Russo, a space scientist at the Johns Hopkins University Applied Physics Laboratory, in a statement.

The team looked at the coma and tail of short-period comets, those who orbit the Sun in less than 200 years, and long-period ones that come from the very edge of the Solar System. The research, published in Icarus, highlights how the abundance of molecules like ammonia and formaldehyde appear to be strongly related to each other and to no other molecule.

They also looked at the emission of water, carbon monoxide, methane, ethane, methanol, and hydrogen cyanide. These molecules are relatively light and the research suggests they are released directly from the nucleus as the comet gets closer to the Sun.

“We want to study the abundances of these chemicals because comets are a window into the distant past, and they can tell us what the chemical characteristics and conditions were like in the early Solar System,” continued Dello Russo.

Although every comet has a unique chemical signature, the team tried to find common ground between different comets. Using specific algorithms, the team was able to divide the sampled objects into four groups and 11 subgroups.

“Comets are very diverse,” he added. “When NASA or ESA sends a mission to a comet, we can learn a tremendous amount of detail on that specific comet. What our research does is put those findings into the larger chemical context of the overall comet population. We can help answer where an individual comet fits into the population of comets.”