Bouncing comets could deposit the building blocks for life on other plants in the galaxy, new research suggests.
One long-standing theory for how the molecular material for life ended up on Earth is that it could have been delivered by comets.
Now researchers from the University of Cambridge have shown how comets could do something similar for other planets.
It’s possible that the molecules that led to life on Earth came from comets, so the same could be true for planets elsewhere in the galaxy
Richard Anslow, University of Cambridge
First author Richard Anslow, from Cambridge’s Institute of Astronomy, said: “We’re learning more about the atmospheres of exoplanets all the time, so we wanted to see if there are planets where complex molecules could also be delivered by comets.
“It’s possible that the molecules that led to life on Earth came from comets, so the same could be true for planets elsewhere in the galaxy.”
Comets need to be travelling relatively slowly – at speeds below 15 kilometres per second – in order to deliver organic matter.
Faster than this, and the essential molecules would not survive, as the speed and temperature of impact would cause them to break apart.
Experts say the most likely place where comets can travel at the right speed are peas in a pod systems.
In these systems – where a group of planets orbit closely together – the comet could essentially be passed or bounced from the orbit of one planet to another, slowing it down.
If travelling slowly enough, the comet would crash on a planet’s surface, delivering the intact molecules that researchers believe are the precursors for life.
According to the researchers, such systems could be promising places to search for life outside our solar system.
Comets are known to contain a range of the building blocks for life, known as prebiotic molecules.
For example, samples from the Ryugu asteroid, analysed in 2022, showed that it carried intact amino acids and vitamin B3.
Comets also contain large amounts of hydrogen cyanide (HCN), another important prebiotic molecule.
The carbon-nitrogen bonds of this molecule make it more durable to high temperatures, meaning it could potentially survive atmospheric entry and remain intact.
Using a variety of mathematical modelling techniques, the researchers determined that it is possible for comets to deliver the precursor molecules for life, but only in certain scenarios.
They suggest that for planets orbiting a star similar to our own sun, the planet needs to be low mass and it is helpful for the planet to be in close orbit to other planets in the system.
The researchers found that nearby planets on close orbits are much more important for planets around lower-mass stars, where the typical speeds are much higher.
In such a system, a comet could be pulled in by the gravitational pull of one planet, then passed to another planet before impact, slowing down with each impact.
The researchers say their results could be useful when determining where to look for life outside the Solar System.
Mr Anslow said: “It’s exciting that we can start identifying the type of systems we can use to test different origin scenarios.
“It’s a different way to look at the great work that’s already been done on Earth. What molecular pathways led to the enormous variety of life we see around us?
“Are there other planets where the same pathways exist? It’s an exciting time, being able to combine advances in astronomy and chemistry to study some of the most fundamental questions of all.”
The research, published in Proceedings of the Royal Society A Mathematical Physical and Engineering Sciences, was supported in part by the Royal Society and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).
