A Study of Dust and Gas at Mars from Comet C/2013 A1 (Siding Spring)
  Although the nucleus of comet C/2013 A1 (Siding Spring) will safely pass Mars in October 2014, the dust in the coma and tail will more closely approach the planet. Using a dynamical model of comet dust, we estimate the impact fluence. Based on our nominal model no impacts are expected at Mars. Relaxing our nominal model's parameters, the fluence is no greater than ~10^-7 grains/m^2 for grain radii larger than 10 {\mu}m. Mars orbiting spacecraft are unlikely to be impacted by large dust grains, but Mars may receive as many as ~10^7 grains, or ~100 kg of total dust. We also estimate the flux of impacting gas molecules commonly observed in comet comae. 
Michael S. P. Kelley, Tony L. Farnham, Dennis Bodewits, Pasquale   Tricarico, Davide Farnocchia
astro-ph.EP