Cambridge scientists doubt role of comets in origin of life on Earth

A group of planetary scientists, astrophysicists, and programmers led by Richard Anslow ran 100,000 simulations of comet bombardment on the young Earth. The period under consideration ranged from roughly 4.5 to 3.5 billion years ago. In laboratory experiments, hydrogen cyanide (HCN) serves as a starting material for producing sugars, lipids, nucleobases, and nucleotides. The median number of impacts after which its concentration on the surface reached at least 10 millimoles per litre was just one. The share of simulations in which this never occurred was 28% (54% according to iXBT.com).

According to the authors' calculations, for the molecules to survive, a comet needed to be of an appropriate size, travel relatively slowly, and strike the surface at a very shallow angle. However, with such an atmospheric entry, comets decelerated more strongly and could break apart before impact. Even the surviving material would quickly be diluted by rain and groundwater. "It's a rather romantic idea, but our results show it is extremely unlikely," Anslow said.

On a planetary scale, the researchers estimate that comets delivered several orders of magnitude less intact HCN than Earth's atmosphere could have produced even under the most unfavourable conditions. Among extraterrestrial sources, asteroids remain, which struck Earth far more frequently. The authors do not rule out a single successful impact.

For Mars, the model yielded 1,061 ± 32 potentially successful impacts, and for Venus, 53 ± 7. The scientists used the parameters of the present-day atmospheres of these planets and emphasise that this does not prove that conditions for life arose there.