Comets that bounce around the universe could be delivering the ingredients for life to alien planets

• Comets may have delivered the seeds of life to Earth, scientists say.
• They could also have delivered similar building blocks of life to other planets.

Comets may hold the secret to finding alien life, according to new research.

Scientists at Cambridge University propose that comets may "bounce" around the universe, carrying the essential ingredients to create life on alien worlds.

If their theory is correct, it could help narrow down the search for exoplanets that have the correct conditions for a comet to deliver the building blocks of life.

"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," said first author Richard Anslow from Cambridge's Institute of Astronomy.

Though it's still not quite clear how life starts on a planet, a leading theory is that comets carry "prebiotic" molecules that can develop into life, provided they land safe and sound on the right planet.

To deliver their organic molecules, these comets need to travel fairly slowly, at about nine miles per second, per a press release accompanying the findings. Any faster and the molecules would be destroyed.

Scientists modeled different scenarios to see how planetary systems and their stars would pull at a traveling comet.

They specifically looked at systems carrying rocky planets around low-mass stars — stars that are smaller than our sun. These types of planets have been studied as prime candidates to carry life.

The study found that, in most cases, a comet speeding through a planetary system around a low-mass star would travel too quickly to seed life on a planet in the habitable zone.

There is one notable exception: if the planet is part of a planetary system called "peas in a pod," where the planets are in very close alignment, this string of planets could slow the comet down as it is captured in its orbit.

"It's like kicking a football all the way across the football pitch in one massive shot versus dribbling it slowly with lots of different kicks between the players," Amy Bonsor, an astrophysicist at the University of Cambridge, told Insider.

"One way to get the velocity really low is to have lots and lots of planets, kick the ball between them, and bring it with that low velocity down to the habitable planet to deliver your organics," said Bonsor, who is an author on the study.

Still, Bonsor said the research suggests a low-mass planetary system is less likely to carry life than a system with a brighter star. In these systems, planets can be farther away from their star, which means the comets don't have to pick up quite so much speed to reach them.

"We're all super excited in the community about the fact that we can find habitable zone planets around low-mass stars. And these are really interesting planets and we should be studying them," she said.

Bonsor added that she's not alone in saying that such planets may be less likely to be habitable than an Earth-like planet around a sun similar to ours.

The findings were published in the peer-reviewed journal Proceedings of the Royal Society A on Tuesday.