Delivery of organics to Mars through asteroid and comet impacts

TL;DR

This study quantifies the carbon flux to Mars from asteroid and comet impacts, showing they contribute significantly to the organics found on Mars and are spatially concentrated around impact sites.

Contribution

First dynamical simulation-based estimation of impact-driven carbon flux from asteroids and comets on Mars, highlighting their role in delivering organics.

Findings

Asteroids deliver approximately 0.05 million kg of carbon annually.

Comets contribute about 0.013 million kg of carbon annually.

Impact ejecta's organics are concentrated within 150 km of impact sites.

Abstract

Given rapid photodissociation and photodegradation, the recently discovered organics in the Martian subsurface and atmosphere were probably delivered in geologically recent times. Possible parent bodies are C-type asteroids, comets, and interplanetary dust particles (IDPs). The dust infall rate was estimated, using different methods, to be between $0.71$ and $2.96 \times 10^6$ kg/yr (Nesvorny et al., 2011, Borin et al., 2017, Crismani et al., 2017); assuming a carbon content of 10% (Flynn, 1996), this implies an IDP carbon flux of $0.07 - 0.3 \times 10^6$ kg/yr. We calculate for the first time the carbon flux from impacts of asteroids and comets. To this end, we perform dynamical simulations of impact rates on Mars. We use the N-body integrator RMVS/Swifter to propagate the Sun and the eight planets from their current positions. We separately add comets and asteroids to the simulations as massless test particles, based on their current orbital elements, yielding Mars impact rates of $4.34\times10^{-3}$ comets/Myr and 3.3 asteroids/Myr. We estimate the global carbon flux on Mars from cometary impacts to be $\sim 0.013 \times 10^{6}$~kg/yr within an order of magnitude, while asteroids deliver $\sim 0.05 \times 10^6$~kg/yr. These values correspond to $\sim 4-19 \%$ and $\sim 17-71 \%$, respectively, of the IDP-borne carbon flux estimated by Nesvorny et al. 2011, Borin et al. 2017 and Crismani et al. 2017. Unlike the spatially homogeneous IDP infall, impact ejecta are distributed locally, concentrated around the impact site. We find organics from asteroids and comets to dominate over IDP-borne organics at distances up to 150~km from the crater center. Our results may be important for the interpretation of in situ detections of organics on Mars.