All Comets in Our Solar System Might Originate in the Same Place, Study Finds

"We know what comets consist of and which molecules are present in them. They vary in composition, but are normally seen as just one group of icy balls. Therefore, I wanted to know whether comets are indeed one group, or whether different subsets can be made," the astronomer said.

During his Ph.D. at Leiden University, Eistrup wondered what would happen if he applied existing chemical models to comets. The research team at Leiden Observatory that he was part of included Kavli Prize winner, Ewine van Dishoeck.

The team developed models for predicting the chemical composition of protoplanetary discs — flat discs of gas and dust surround stars in early formation. Conveniently, these Leiden models also turned out to be helpful in providing some insights into the origin of comets.

"I thought it would be interesting to compare our chemical models with published data on comets," the astronomer said.

"Luckily, I had the help of Ewine. We did some statistics to pin down if there was a special time or place in our young solar system, where our chemical models meet the data on comets."

It turned out that this was the case, and to a surprising degree. All fourteen comets tested showed the same trend. "There was a single model that fitted each comet best, thereby indicating that they share their origin."

Originating near our Sun

The origin the researchers pinpointed is somewhere near our young Sun, at a time when it was encircled by a protoplanetary disc and our planets were in the earliest stages of their formation.

The model suggested an area surrounding the Sun, at the range where carbon monoxide is in its ice form — relatively far from the early Sun.

"At these locations, the temperature varies from 21 to 28 Kelvin, which is around minus 250 degrees Celsius. That's very cold, so cold that almost all the molecules we know are ice.

"From our models, we know that there are some reactions taking place in the ice phase—although very slowly, in a time-frame of 100,000 to 1 million years. But that could explain why there are different comets with different compositions."

The researchers say that though the comets seem to have originated in the same place, their orbits could have been disturbed by the gravity of different planets and space objects — this accounts for the different locations and orbits of the comets in our solar system.

Eistrup wishes to follow up this research with larger sample sizes — he concedes that only testing fourteen comets is quite a small sample size.

This research might provide insight into our own origin. "We still don't know how life on Earth began," Eistrup says. "But the chemistry on comets could lead to the production of organic molecules, including some building blocks for life. And if the right comet hits the right planet, with the right environment, life could start growing." We might just have been the right planet.