Simulations suggest comet delivery of prebiotic chemicals to early Earth was extremely unlikely
Computer models indicate that the chance of comets bringing enough hydrogen cyanide to spark life on Earth was very low, though the scenario may be more plausible for Mars.
A study published in Scientific Reports used 100,000 computer simulations to evaluate whether comets could have delivered the prebiotic molecule hydrogen cyanide to early Earth. Hydrogen cyanide, which has been detected in comets, can serve as a building block for lipids, sugars and nucleic acids.
The simulations showed that in 54% of cases no comet impact delivered a sufficient amount of the molecule to land, as most comets disintegrated in the atmosphere or struck the oceans, diluting any surviving chemicals. In the remaining 46% of runs, at least one impact could have deposited enough hydrogen cyanide, but the opportunity for subsequent chemistry would have been brief.
"It would really have to be a one-in-a-million occurrence, because not only would you need an impact at just the right speed and just the right angle, you would also need everything to happen after that point, in terms of the concentration and the speed at which the chemical origins of life got going," said astronomer Richard Anslow of the University of Cambridge.
The authors caution that the results do not prove the hypothesis false, but they suggest that cometary delivery was a rare event on Earth. The same models indicated that Mars, with its thinner atmosphere and lower impact velocities, could have experienced five times more successful deliveries, whereas Venus’s dense atmosphere would likely destroy incoming comets.