Christian theologians have always reflected on various aspects of Christian doctrine with reference to an abundant cosmic hierarchy, from the fish of the sea to the seraphic host of heaven. Angelology, for example, is not simply a study of the nature of spiritual creatures or ‘intelligences’ as they are attested in scripture. By thinking about angels who lack bodies, we can thereby think about the meaning and significance of the body for theological anthropology. Are angels more in the image of God than humans because angels, like God, are immaterial? In some respects, yes, answers Thomas Aquinas. In other respects, no: the bodily nature of human beings gives the power to reproduce and thereby share more deeply in the creativity of God. Thinking about the human person in relation to another kind of intelligent life in the angelic – a kind of theological thought experiment – yields a positive evaluation of the human body. This leads to the claim that the human person is a ‘microcosm’ of creation incorporating all aspects of the cosmic order, sharing the material nature of terrestrial creatures and the spiritual nature of angels.

Andrew Davison’s Astrobiology and Christian Doctrine is a similar kind of theological thought experiment centred on the abundant richness of creation. It is not provoked by the description of a cosmic hierarchy in scripture and early Christian writings, but by contemporary cosmology’s rapidly growing ability to identify billions of galaxies and planetary systems which might harbour life. This has given rise to the field of astrobiology (sometimes known as exobiology) as the scientific study of life as a cosmic phenomenon. Although theologians have reflected on the implications of biological life beyond the earth since at least the fifteenth century, the salience of theology’s engagement with astrobiology has increased with the discovery of billions of potentially life-bearing planetary systems since the 1990s.

The possibility of life beyond earth, particularly intelligent life, raises interesting theological questions about the nature and extent of revelation, theological anthropology, Christology, and salvation. For example, if there is intelligent life on other planets that is estranged from God by sin, would multiple incarnations on other planets be required for God to effect salvation? Christology and salvation is one of the five key theological themes tackled by Davison, and perhaps the most discussed in the current literature on theology and astrobiology. It reaches the heart of traditional Christological debates concerning the tension between Christ’s particularity – this historical man Jesus of Nazareth – and Christ’s universality – the one in whom and through whom all things were made, who died and rose again that all might be saved. If the eternal Word was incarnate in Jesus Christ, died and rose again for our salvation, is this economy sufficient for the salvation of all intelligent life in the cosmos? The answer given by Davison reflects his fidelity throughout the book to the theology of Thomas Aquinas. For Aquinas, the incarnation of God is not a matter of necessity (God did not have to be incarnate to save us) or caprice (the incarnation is not a matter of divine whim), but ‘fittingness’ (convenientia). This is an aesthetic understanding of the incarnation. It is fitting that God is incarnate as a human person for our salvation because it is humanity that has sinned. Whereas God could have saved humanity by an act of his sovereign will, it is more fitting that our salvation be effected through the incarnation so that we can know about it and participate in it. The means of our salvation is fitting to the goal of our salvation, which is a share in the divine life. Extending this logic, Davison is open to the possibility of multiple incarnations so that intelligent life on other planets can know about, and participate in, God’s salvific action (p.315). He extends this reflection to another theological thought experiment related to a counterfactual: would God have been incarnate, if humanity had not fallen? His answer (on this occasion somewhat counter to Aquinas’s view) is ‘yes’.

Davison’s work is always clear and rigorous. In deploying Aquinas’s theology faithfully and imaginatively, he makes the power of that theology evident in extending theological reflection to astrobiology. At the same time, Davison reveals the deficiencies of other theological approaches to astrobiology that lack firm moorings in scripture and the Christian tradition. Of course, we have not yet discovered extraterrestrial life, let alone intelligent life. Whilst one appreciates Davison’s desire to get ahead of the game and commence some kind of theology of cosmic life ahead of our discovery of extraterrestrial life, the field of theology and astrobiology has a highly speculative ‘what if?’ character. It is useful in clarifying aspects of Christian teaching, but so much seems to depend on the nature of the life we might discover on other planets. Of that, we know nothing and speculate, on the basis of the life we do know. We already do this very fruitfully in fantasy and science fiction. Theology and astrobiology is a similar exercise in stretching the theological imagination.