  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.
