Comets may bring ingredients for life most easily to clustered planets

It may be easiest to deliver the ingredients for life to planets with close neighbours. Comets can carry many of the key building blocks for life, including amino acids and other organic compounds – but whether they can deliver those building blocks to any given planet may depend on the arrangement of its broader system.

There are several ideas for how the ingredients for life came to be on Earth, but a popular one is that comets smashed into the planet and deposited organic molecules here. However, comets tend to move through space at extreme speeds, and if they smash into a planet at upwards of about 20 kilometres per second, the possibility of those crucial compounds surviving the collision are low to nil.

Richard Anslow at the University of Cambridge and his colleagues performed a series of simulations investigating how planetary systems could slow down comets, bringing the impact speeds down enough to preserve these compounds. In ideal circumstances, a slow collision would leave behind a sort of prebiotic soup called a comet pond inside the impact crater.

They found that there are two types of systems capable of slowing down comets by 5 to 10 kilometres per second: those with relatively massive stars, where everything tends to orbit a bit slower, and those where several planets are spaced close together like peas in a pod, so a comet can weave among them and lose speed over time.

“The very best planetary system would be on a relatively low-mass planet like Earth around a high-mass star, similar to our sun but maybe even higher mass, and in a planetary system where it’s nearby to other rocky planets so they can pass comets around,” says Anslow.

He says that if astronomers do eventually detect signs of life on other worlds, this could help us figure out how it got there simply by examining the arrangement of the system as a whole – which could in turn boost our limited understanding of how life formed on Earth.