Overview
- The study, led by Richard Anslow and published Oct. 28 in Scientific Reports, used integrated dynamical, atmospheric-entry and impact models to test whether comets could deliver hydrogen cyanide to early Earth.
- Researchers treated hydrogen cyanide (HCN) as a proxy for fragile prebiotic organics and found most comet impacts generate enough heat from high entry speeds and steep angles to destroy or disperse these molecules.
- Model results identify a survival threshold near 15 km/s and show successful, abundant delivery would be vanishingly rare, a scenario the team described as effectively a one-in-a-million occurrence.
- Evidence from asteroid samples, including OSIRIS-REx material from Bennu that contains RNA precursors, and the greater frequency of asteroid impacts strengthen asteroids as a more likely extraterrestrial source.
- The authors note key caveats: the models focus on HCN only, assume particular early-Earth atmospheres and comet populations, allow for extremely rare low-speed deliveries, and suggest Mars and some exoplanet systems could be more favorable for cometary delivery.