Constraining the survival of HCN during cometary impacts

TL;DR

This study uses impact simulations and chemical modeling to evaluate the likelihood of cometary impacts delivering surviving HCN molecules to early Earth, highlighting the impact velocity and angle constraints for prebiotic chemistry relevance.

Contribution

It provides a new parametrization of HCN survival probability based on impact conditions, improving understanding of cometary delivery of prebiotic molecules.

Findings

HCN survival is limited at impact velocities above Earth's escape velocity.

Extreme impact obliquity increases HCN survival chances.

Delivery alone may not suffice for prebiotic chemistry initiation.

Abstract

Cometary impacts have been invoked as an atmosphere-independent method of stockpiling hydrogen cyanide (HCN), a key prebiotic feedstock molecule, into environments favourable for the onset of prebiotic chemistry on the early Earth. This work revisits the prospects for cometary delivery of HCN through new impacts simulations of idealised cometary bodies using the shock physics code iSALE combined with simple chemical modelling. Using temperature and pressure profiles for material within spherical, non-porous comets with a high resolution of Lagrangian tracer particles, we assess the survival rate of HCN across a range of impact velocities, sizes and angles, assuming both steady state and equilibrium chemistry. We find that HCN survival is extremely limited at impact velocities above the escape velocity of the Earth, unless the impact occurs at extreme obliquity ($\theta \sim 15^\circ$). We present a parametrisation of the survival of HCN as a function of impact velocity, angle, and cometary diameter, which provides an upper limit to survival in more realistic scenarios to aid with future studies investigating the role of comets in the origins of life. Although successful HCN delivery may be possible in our idealised model, we neglect to consider the effect of atmospheric passage and our results suggest that delivery alone is not likely to be sufficient for the onset of prebiotic chemistry.