I argue that the attempts of astrobiologists and philosophers to provide an ethical justification for planetary protection policies (in particular, those aspects of policy concerning forward contamination) suffer from a ‘life bias’ in that reasons for protection are regarded as genuinely ethical only when they include some kind of direct moral consideration for extraterrestrial life. There are, I maintain, good reasons for the protection of space environments, including the protection of sites of interest to disciplines other than astrobiology. These reasons are no less ethical simply because their aim is something other than the protection of extraterrestrial life. While the possible existence of such reasons has been recognized, they have yet to be developed in a philosophically satisfying way. This paper aims to fill this lacuna by motivating and articulating an ethical perspective which recommends broader protection of the space environment. Long-range implications for such a broadening of planetary protection are considered, including implications for interstellar exploration.

Previous work in studying interstellar exploration by one or several probes has focused primarily either on engineering models for a spacecraft targeting a single star system, or large-scale simulations to ascertain the time required for a civilization to completely explore the Milky Way Galaxy. In this paper, a simulated annealing algorithm is used to numerically model the exploration of the local interstellar neighbourhood (i.e. of the order of ten parsecs of the Solar System) by a fixed number of probes launched from the Solar System; these simulations use the observed masses, positions and spectral classes of targeted stars. Each probe visits a pre-determined list of target systems, maintains a constant cruise speed, and only changes the direction from gravitational deflection at each target. From these simulations, it is examined how varying design choices – differing the maximum cruise speed, number of probes launched, number of target stars to be explored, and probability of avoiding catastrophic system failure per parsec – change the completion time of the exploration programme and the expected number of stars successfully visited. In addition, it is shown that improving this success probability per parsec has diminishing returns beyond a certain point. Future improvements to the model and possible implications are discussed.