This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The theory that comets delivered the molecular building blocks for life on Earth is a long-standing one, since comets are known to carry many of these molecules. However, a new study challenges this idea.
The researchers, led by the University of Cambridge, found the cometary delivery of these building blocks would be—at best—a 'one-off fluke,' and not the steady rain of prebiotic molecules that had been theorized. Using computer modeling, the researchers determined that comets travel too fast and at too sharp an angle to Earth's atmosphere for the fragile organic molecules to survive: they would almost certainly vaporize on impact with the surface. However, the researchers also found that another planet in our system—Mars—could be a slightly more promising candidate for cometary delivery of prebiotic molecules, although this is still highly unlikely.
The results are published in the journal Scientific Reports. "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 lead author Dr. Richard Anslow from Cambridge's Institute of Astronomy.
"It's kind of a romantic idea, but our results suggest it's highly unlikely." In 2023, Anslow and several of his co-authors on the current paper theorized that in systems where planets orbit closely together, comets might slow down by 'bouncing' from one planet to the next, delivering organic molecules as they went. Building on the earlier study, Anslow and his colleagues investigated whether such a scenario might be possible in our own solar system. "We're learning more and more all the time about how our solar system and the Earth formed, and pulling this together with lots of different advances in modeling, which allowed us to investigate this idea that has been around for close to a century," he said.
However, the new study shows just how rare that scenario is. The researchers used recent advances in comet impact simulations, comet-atmosphere interactions and dynamic modeling of the origin and evolution of comets to conduct their study. Taken together, the researchers found that while the successful delivery of prebiotic molecules cannot be ruled out completely, it would be extremely unlikely.
For their study, the researchers focused on hydrogen cyanide (HCN), an important prebiotic molecule that is regularly found on solar system comets. Their simulations showed that even in the rare event that HCN molecules survived impact with Earth, impacts delivering a useful concentration were extremely uncommon. The number of comets hitting the Earth declined rapidly in our planet's first 500 million years, and there were, at most, a handful of opportunities in Earth's early history for HCN delivery on a comet.
Extract — continue reading at the source.
