  In this work we consider the potential of cometary impacts to deliver complex
organic molecules and the prebiotic building blocks required for life to rocky
exoplanets. Numerical experiments have demonstrated that for these molecules to
survive, impacts at very low velocities are required. This work shows that for
comets scattered from beyond the snow-line into the habitable zone, the minimum
impact velocity is always lower for planets orbiting Solar-type stars than
M-dwarfs. Using both an analytical model and numerical N-body simulations, we
show that the lowest velocity impacts occur onto planets in tightly-packed
planetary systems around high-mass (i.e. Solar-mass) stars, enabling the intact
delivery of complex organic molecules. Impacts onto planets around low-mass
stars are found to be very sensitive to the planetary architecture, with the
survival of complex prebiotic molecules potentially impossible in
loosely-packed systems. Rocky planets around M-dwarfs also suffer significantly
more high velocity impacts, potentially posing unique challenges for life on
these planets. In the scenario that cometary delivery is important for the
origins of life, this study predicts the presence of biosignatures will be
correlated with i) decreasing planetary mass (i.e. escape velocity), ii)
increasing stellar-mass, and iii) decreasing planetary separation (i.e.
exoplanets in tightly-packed systems).
