Researchers from the University of Cambridge have shown how comets could deposit building blocks for life on other planets in the galaxy.
To deliver organic material, comets need to be travelling at speeds below 15km per second. The essential molecules would not survive at higher speeds because the speed and temperature would cause them to break apart.
Comets can travel at the right speed in ‘peas in a pod’ systems where planets orbit closely together. In the right system, the comet can be passed from one planet’s orbit to another, causing it to slow down.
The comet would crash on a planet’s surface if it travelled at slow enough speeds, delivering the building blocks for life.
The research, ‘Can comets deliver prebiotic molecules to rocky exoplanets?’ suggests that such systems would be potential areas to search for life outside our Solar System.
Comets contain the building blocks for life
Comets contain the building blocks for life, known as prebiotic molecules. For example, samples from the Ryugu asteroid showed that it carried intact amino acids and vitamin B3.
Comets also contain large amounts of hydrogen cyanide. Hydrogen cyanide is another prebiotic molecule durable to high temperatures, meaning that it can survive atmospheric entry and remain intact.
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.”
The team do not believe that comets are necessary to the origin of life on Earth or other planets but wanted to limit the types of planets where comets could deliver complex molecules.
Most of the comets in our Solar System sit in the Kuiper Belt. When comets or other objects in the Kuiper Belt collide, they can be pushed by Neptune’s gravity towards the Sun and get pulled in by Jupiter’s gravity.
Some of these comets make their way into the inner Solar System.
Can comets deliver the molecules for life?
“We wanted to test our theories on planets that are similar to ours, as Earth is currently our only example of a planet that supports life,” said Anslow. “What kinds of comets, travelling at what kinds of speed, could deliver intact prebiotic molecules?”
The researchers used mathematical modelling techniques to determine that comets can deliver the precursor molecules for life but only in certain scenarios.
To orbit a star similar to our Sun, a planet needs to be low mass and in close orbit to other planets in the system. The team found that planets in close orbits are much more critical for planets around lower-mass stars.
In such a system, a comet could be pulled in by the gravitational pull of one planet then passed to another planet before impact. If this comet passing happened enough, the comet would slow down to allow prebiotic molecules to enter the planet.
“In these tightly-packed systems, each planet has a chance to interact with and trap a comet,” said Anslow. “It’s possible that this mechanism could be how prebiotic molecules end up on planets.”
For planets in orbit around lower-mass stars, it would be more difficult for complex molecules to be delivered by comets. In these systems, rocky planets suffer more high-velocity impacts – posing challenges for life on these planets.
The results could help find life outside the Solar System
The team believe that the results have the potential to determine where to look for life outside the Solar System.
“It’s exciting that we can start identifying the type of systems we can use to test different origin scenarios,” said Anslow.
“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.”
