“Where do comets come from?”
It’s one of those children’s bedtime questions (not as bad as the BIG one about babies) that can be answered (up to a certain age) with “Ask your mother,” but will still keep you up all night wondering where DO comets come from? A new study gives the answer … at least for our solar system – interstellar comets are a different animal (rock) and require more study. For the next time the question comes up, here’s your answer:
“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. There was a single model that fitted each comet best, thereby indicating that they share their origin.”
Yeah, that will satisfy your child’s curiosity … not. While working on his PhD at Leiden University in the Netherlands, astronomer Christian Eistrup wondered if the icy balls orbiting the sun in various strange and sundry paths might have similar chemical compositions, which might give a hint to where they came from and when.
Fortunately, he had access to the Leiden Observatory (astronomical institute of Leiden University) and Ewine van Dishoeck, the observatory’s 2018 Kavli Prize winner “”for her combined contributions to observational, theoretical, and laboratory astrochemistry, elucidating the life cycle of interstellar clouds and the formation of stars and planets.” Eistrup had already developed models to predict the chemical composition of protoplanetary discs – those flat discs of gas and dust around young stars that eventually coalesce to form planets or get eaten by the star. After meeting van Dishoeck, Eistrup had his “A-ha!” moment.
“I thought it would be interesting to compare our chemical models with published data on comets. Luckily, I had the help of Ewine.”
Using chemical data on 14 different and well-known comets, the team worked backwards to find a time when they matched and were surprised to find one that fit all 14. That was the cometary nursery. Not surprisingly, it existed when the Sun was still young as well. The model showed a cold zone around the Sun (although far from it) measuring between 21 to 28 Kelvin (around -250 Celsius or around -420 F). At that temperature, everything was an ice molecule, but some chemical reactions were still taking place, resulting in cometary siblings with differing compositions. Their early cometary DNA model also revealed a rather ‘disturbing’ reason for their subsequent differing locations and trajectories:
“Although we now think they formed in similar locations around the young Sun, the orbits of some of these comets could be disturbed—for instance by Jupiter—which explains the different orbits.”
The results were accepted recently by the journal Astronomy & Astrophysics and summarized in a university press release. If you’re raising an astute and science-oriented child, they will no doubt ask a follow-up question after your “Comets come from an ice ring that circled the Sun when it was young” answer: Could one of these comets have life forms on it which it could bring to Earth in a collision?
“We still don’t know how life on Earth began. 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.”
Make sure you give credit to Christian Eistrup and tell your child to direct all future bedtime questions to him at Leiden Observatory, where he’s looking for more comets to model.