Cambridge Study Says Comets Unlikely Source of Earth’s Prebiotic Hydrogen Cyanide

Overview

• A University of Cambridge paper published in late October used large ensembles of integrated simulations to quantify how often comets could deliver hydrogen cyanide (HCN), a key prebiotic feedstock.
• The team found most comets strike too fast and at steep angles so they break up in airbursts or vaporize on impact, which destroys fragile organics before they reach the surface.
• When surviving material is mixed into an ocean or global water inventory the models show HCN concentrations would be far below levels thought necessary to trigger the chemical steps toward life.
• The authors point to carbon‑rich asteroids or chemical synthesis on early Earth (for example in hydrothermal systems) as more plausible sources and say Mars would be a comparatively better target for intact cometary delivery because of its smaller size and thinner atmosphere.
• The paper stresses model limits and does not fully rule out extremely rare, precisely timed comet events, and it suggests the result should guide where telescopes and astrobiologists focus searches for life’s precursors.