Historically, scientists thought that comets were important for the origin of life on Earth, because they carried carbon and nitrogen-bearing molecules, so these giant space snowballs were almost like a ‘get out of jail free card’ that brought all the molecules a planet would need to seed life,
said Dr. Richard Anslow, lead author of a new study published in Scientific Reports on 28 October 2026, according to Sciencedaily.
New computer simulations led by researchers at the University of Cambridge challenge the century-old idea that comets delivered life’s chemical building blocks to early Earth. The modeling shows that icy comets typically hit the planet at speeds and angles too violent for delicate organic molecules to survive SciTechDaily reports.
Authored by Richard Anslow alongside peers at the University of Cambridge’s Institute of Astronomy and the University of Edinburgh, the findings are published in the journal Scientific Reports under the title Cometary impacts an unlikely pathway towards the origins of life on Earth.
While the broader idea of panspermia—the hypothesis that life’s components originated in outer space—was formally put forward in 1908, the specific notion that comets brought Earth’s biological foundations traces back at least as far as 1961. This current inquiry builds upon prior work from 2023, during which Anslow and several co-authors suggested that closely positioned planets might assist comets in transporting organic compounds.
Simulating Early Earth Bombardment
Researchers modeled the early Solar System’s bombardment across 100,000 simulated histories to track how often comets could deliver hydrogen cyanide to dry land Chemical & Engineering News notes. Operating in million-year increments, the investigators ran the full bombardment simulation 100,000 times, exclusively counting impacts on terrestrial landmasses since any cyanide landing in the ocean would instantly become diluted.
Scientists calculate that more than 4 billion years ago, the primordial Earth endured an intense bombardment phase featuring upwards of 100,000 comets exceeding 100 metres (328 feet) in size.
Hydrogen cyanide, a substance highly valued by origin-of-life chemists, is abundantly transported by comets. Due to their typical trajectories and velocities upon approaching Earth, however, comets make it exceptionally difficult for such fragile organic compounds to endure the impact.
Why Mars Faced Different Odds
When researchers ran the same bombardment simulations on neighboring worlds, the findings suggest that Mars may have offered slightly better conditions for receiving these molecules. The model recorded 744 such impacts on Mars compared to only 87 for Earth, largely because comets collided with the Red Planet at lower speeds while its thin atmosphere allowed them to pass through intact.
Because Mars is smaller than Earth and features a much lighter atmosphere today, frequent visitor comets would have had a higher probability of reaching its surface in the past.
This is not to say it definitely happened on Mars, of course, but suggests it would be unlikely if it happened on Earth and didn’t happen on Mars,
said Anslow, adding that the other, perhaps more likely, alternative, is that it didn’t happen on either planet
SciTechDaily reports.
Harvard astrophysicist Avi Loeb noted that Mars may have been successfully infused by comets before asteroids from the Red Planet landed on Earth, adding a sense of cosmic modesty regarding natural processes from billions of years ago.
Alternative Origins for Prebiotic Chemistry
With comets ruled out as a steady supplier, scientists point to alternative sources like asteroids, which collided with early Earth far more frequently ScienceDaily reports. Another possibility is that Earth produced these chemical precursors entirely on its own through natural planetary processes ScienceDaily reports.
César Menor-Salván, an astrobiologist at the University of Alcalá in Spain who was not involved in the research, noted that the paper calculates rather than proves that intact delivery of concentrated cyanide is unlikely.
Funding for the project came partially from the Royal Society, the Leverhulme Centre for Life in the Universe, and the Science and Technology Facilities Council (STFC), which operates as a division of UK Research and Innovation (UKRI).