Comets may be a key source for the building blocks of life, but the only planetary systems where those ingredients could survive impact may be ones with large stars or lots of neighbouring worlds

The James Webb Space Telescope has let us peer into the atmosphere of gas giant planet WASP-107b, and it has clouds made of sand and an atmosphere of sulphur dioxide and water vapour

Potassium and rubidium atoms aboard the International Space Station have been cooled almost to absolute zero to put a fundamental principle of Einstein’s general theory of relativity to the ultimate test

The Euclid telescope will spend six years in space, creating a 3D map of galaxies formed around 10 billion years ago. Find out more here.

In order to deliver organic material, comets need to be travelling relatively slowly – at speeds below 15 kilometres per second. At higher speeds, the essential molecules would not survive – the speed and temperature of impact would cause them to break apart.

The most likely place where comets can travel at the right speed are ‘peas in a pod’ systems, where a group of planets orbit closely together. In such a system, the comet could essentially be passed or ‘bounced’ from the orbit of one planet to another, slowing it down.

At slow enough speeds, the comet would crash on a planet’s surface, delivering the intact molecules that researchers believe are the precursors for life. The results, reported in the Proceedings of the Royal Society A, suggest that such systems would be promising places to search for life outside our Solar System if cometary delivery is important for the origins of life.

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 strong carbon-nitrogen bonds of HCN make it more durable to high temperatures, meaning it could potentially survive atmospheric entry and remain intact.

“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,” said first author Richard Anslow from Cambridge’s Institute of Astronomy. “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 researchers do not claim that comets are necessary to the origin of life on Earth or any other planet, but instead they wanted to place some limits on the types of planets where complex molecules, such as HCN, could be successfully delivered by comets.

Most of the comets in our Solar System sit beyond the orbit of Neptune, in what is known as the Kuiper Belt. When comets or other Kuiper Belt objects (KBOs) collide, they can be pushed by Neptune’s gravity toward the Sun, eventually getting pulled in by Jupiter’s gravity. Some of these comets make their way past the Asteroid Belt and into the inner Solar System.

“We wanted to test our theories on planets that are similar to our own, 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?”

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. 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. If this ‘comet-passing’ happened enough times, the comet would slow down enough so that some prebiotic molecules could survive atmospheric entry.

“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, such as M-dwarfs, it would be more difficult for complex molecules to be delivered by comets, especially if the planets are loosely packed. Rocky planets in these systems also suffer significantly more high-velocity impacts, potentially posing unique challenges for life on these planets.

The researchers say their results could be useful when determining 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.”

The research was supported in part by the Royal Society and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). Richard Anslow is a Member of Wolfson College, Cambridge.

 

Reference:
R J Anslow, A Bonsor and P B Rimmer. ‘Can comets deliver prebiotic molecules to rocky exoplanets?’ Proceedings of the Royal Society A (2023). DOI: 10.1098/rspa.2023.0434

How did the molecular building blocks for life end up on Earth? One long-standing theory is that they could have been delivered by comets. Now, researchers from the University of Cambridge have shown how comets could deposit similar building blocks to other planets in the galaxy.

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 galaxyRichard Anslowsolarseven via Getty ImagesArtist's impression of a meteor hitting Earth

The text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright ©University of Cambridge and licensors/contributors as identified.  All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

The tail of comet Erasmus swung back and forth during its closest approach to the sun, probably because of a cloud of plasma spat out during a solar storm

Cosmologists have come to see the early universe as a whole series of transformations, or phase transitions, opening the door to intriguing possibilities for what really happened during the big bang

Hiranya Peiris is Cambridge’s new Professor of Astrophysics (1909). She discusses being inspired by Stephen Hawking, the unknown space before you arrive at an answer, and high-risk high-reward research. She is an alumna and Fellow of Murray Edwards College.

Nature, Published online: 10 November 2023; doi:10.1038/d41586-023-03399-3

An object that orbits the Sun beyond the main asteroid belt and occasionally sports a tail is spotted in archival images.

Explaining the structure and evolution of stars may seem as esoteric as can be, but there are many applications for this knowledge in our day-to-day lives, says Chanda Prescod-Weinstein

The most distant supermassive black hole confirmed is more than 31 billion light years away, and it could be the key to figuring out how these behemoths grew so big so fast

The quantum realm is full of strange effects, but there’s a reason why everything looks normal from our point of view, writes physicist Sebastian Deffner

Nature, Published online: 08 November 2023; doi:10.1038/d41586-023-03498-1

A spiral galaxy and the Horsehead Nebula are among the first pictures released by ESA’s Universe-mapping observatory.

Nature, Published online: 08 November 2023; doi:10.1038/d41586-023-03275-0

Observations have shown that some dwarf galaxies lose their stars through interactions with more massive galaxies. The dense nuclei that remain are ultra-compact dwarf galaxies, the origin of which has long been a subject of debate.

Nature, Published online: 08 November 2023; doi:10.1038/s41586-023-06636-x

We report observations of ceers-2112 that show that this galaxy, at a redshift of 3, unexpectedly has a barred spiral structure.

Nature, Published online: 08 November 2023; doi:10.1038/s41586-023-06650-z

In the Virgo galaxy cluster, we identified a continuum of objects that maps the morphological transition between nucleated dwarf galaxies and ultra-compact dwarf galaxies (UCDs), providing evidence for the formation of UCDs through tidal stripping of ancient dwarf galaxies.

Nature, Published online: 08 November 2023; doi:10.1038/s41586-023-06616-1

We report the presence of gas-phase phosphorous at the edge of the Galaxy and suggest it is produced by neutron-capture processes in lower mass asymptotic giant branch stars.

Nature, Published online: 06 November 2023; doi:10.1038/d41586-023-03475-8

Data from the James Webb and Chandra space telescopes reveal a massive object in a galaxy that formed less than half a billion years after the Big Bang.

From the Great Red Spot to the extreme jet stream, Jupiter’s weather is intense, but that's nothing compared to the extraordinary storms and winds on other gas giants in the universe

The most distant Milky Way-like galaxy ever seen – a barred spiral galaxy – has been spotted by the James Webb Space Telescope and it is more than 11 billion years old