For decades, comets have been considered possible carriers of molecules that could have helped kick-start life on Earth. But a study led by the University of Cambridge suggests that transporting these compounds was not enough: they also had to survive atmospheric entry and impact in concentrations useful for prebiotic chemistry.
Published on October 28 in Scientific Reports, the research focused on hydrogen cyanide (HCN), a molecule involved in several proposed pathways of prebiotic chemistry. The team modelled comet evolution, passage through the atmosphere and the destruction of HCN on impact.
Across 100,000 simulations, 54% showed no impact that delivered HCN at a concentration considered relevant, accounting for the availability of land. The researchers also identify ocean impacts as a challenge, since surviving material could be diluted. Comet impacts became less frequent over time, further limiting the opportunities for successful delivery.
The study suggests that fragile molecules would be unlikely to survive an impact with Earth’s surface. Finding organic compounds in a comet, therefore, does not establish that they reached a place where they could take part in reactions leading to life.
Mars could be more favourable for this particular delivery mechanism. Its lower gravity and thinner atmosphere may make it easier for comet-borne material to survive. The researchers do not conclude that life began on Mars; their comparison concerns only the delivery of molecules.
Comets remain a possible source, but the findings suggest they were not a simple or dependable route. Asteroids, which also carry organic compounds, and molecules formed on Earth itself are among the alternatives described in the report.
Sources: Pplware.