Study finds comets unlikely to deliver HCN to early Earth

A University of Cambridge-led study concludes that comet impacts were highly unlikely to deliver hydrogen cyanide to early Earth in concentrations useful for prebiotic chemistry, though the researchers say the possibility cannot be ruled out. The team used computer simulations to examine whether hydrogen cyanide, or HCN, could survive a comet’s passage through the atmosphere and impact with the surface. HCN is found in comets and can help produce sugars, lipids and components of genetic material in laboratory experiments when present at sufficient concentrations. The researchers treated HCN as a relatively robust test case because its strong carbon-nitrogen bond makes it more resistant to destruction than many more complex organic molecules. Their results suggest that small comets can break apart in the atmosphere, while larger ones can strike at speeds and temperatures that destroy much of their chemical cargo. Even when HCN survives, the amount may not be concentrated enough to support subsequent chemistry. The study’s conclusion is based on simulations, not direct evidence that cometary delivery did or did not occur. The researchers said a successful impact remains...