Cambridge Study Says Comets Unlikely to Have Delivered Earth's Prebiotic Molecules

Overview

• A University of Cambridge paper published in Scientific Reports reports that integrated dynamical and impact simulations show most comet impacts would vaporize or disperse hydrogen cyanide before it reached early Earth.
• The study used about 100,000 simulated bombardment histories and found many typical comet arrivals hit too fast or at steep angles, causing high-altitude airbursts and fragmentation that dilute fragile organics.
• Authors say comets could not have been a steady source of concentrated HCN and that any successful delivery would be an extremely rare, narrowly conditioned event rather than a reliable supply.
• The team highlights alternative explanations for Earth's feedstock, including delivery by carbon-rich asteroids and local synthesis in hydrothermal or surface chemistry, and points to Mars as a more favorable target for intact comet deliveries.
• The work is model-based and limited to hydrogen cyanide and specific early-environment assumptions, so it reframes priorities for lab studies and telescope searches without closing the comet-delivery question entirely.