  We present a simple model for estimating the probability of interplanetary
panspermia in the recently discovered system of seven planets orbiting the
ultracool dwarf star TRAPPIST-1, and find that panspermia is potentially orders
of magnitude more likely to occur in the TRAPPIST-1 system compared to the
Earth-to-Mars case. As a consequence, we argue that the probability of
abiogenesis is enhanced on the TRAPPIST-1 planets compared to the Solar system.
By adopting models from theoretical ecology, we show that the number of species
transferred and the number of life-bearing planets is also likely to be higher,
because of the increased rates of immigration. We propose observational metrics
for evaluating whether life was initiated by panspermia on multiple planets in
the TRAPPIST-1 system. These results are also applicable to habitable
exoplanets and exomoons in other planetary systems.
