The search for extraterrestrial life is one of the most exciting frontiers in present-day astronomy. Recently, the TRAPPIST-1 star was discovered to host seven rocky planets with masses and radii similar to those of the Earth, of which at least three of them may be capable of supporting life. Our paper addresses the possibility that life on one of these planets can spread to others through the transfer of rocky material. We conclude that this process has a high probability of being operational, implying that this planetary system may possess multiple life-bearing planets. Thus, our work has profound theoretical and observational consequences for future studies of the TRAPPIST-1 system and the likelihood of life in our galaxy.

Abstract

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 with the Earth-to-Mars case. As a consequence, we argue that the probability of abiogenesis is enhanced on the TRAPPIST-1 planets compared with the solar system. By adopting models from theoretical ecology, we show that the number of species transferred and the number of life-bearing planets are 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.