You don’t have to search the interwebs very long to find a lively discussion on what effects the discovery of extraterrestrial life would have on Christian theology. For this child of the ’80s, whose first memory of the theater involved E.T. jumping out of a cornfield, this hypothetical question is fascinating. Most answers I read fall under the category of creation, where the consensus is that such a discovery poses no difficulty: God created all things so if aliens do exist, then they must be a part of God’s good creation.

However one assesses this conclusion, we must recognize the traditional nature of this method. Theologians have long engaged the exercise of rethinking biblical interpretations and theological conclusions in light of new knowledge gained from empirical data. The most well-known example has been the rereadings of passages describing the cosmos in the light of scientific models of the universe. So whereas biblical descriptions of the rising and setting sun once supported a geocentric understanding of the universe, post Copernicus and Galileo such passages are read metaphorically. Somewhat more controversial are the rereadings of Genesis 1 in light of the theory of evolution. While metaphorical readings of Genesis 1 date back at least to the third century, they have surged in the last few decades, coinciding with a general reassessment of the relationship of evolution and the doctrine of creation (crystalized in Pope John Paul II’s 1996 statement that evolution is compatible with Christian faith). Indeed, perhaps the only reason there is still some controversy here is that the theory of evolution is relatively new. It could be that in 100 years no one will question evolution, and literal readings of Genesis 1 will look as quaint and misguided as the Catholic Church’s condemnation of Galileo looks today.

Admittedly, this method could appear as a way of “moving the goalposts,” Christians simply change their beliefs to match science. In reality, however, this method is born from the deeply Christian tradition of the liber naturae (“book of nature”), which states that God can be seen and understood in his creation. “The heavens declare the glory of God,” says Psalm 19, “the skies proclaim the work of his hands.” Accordingly, empirical knowledge gathered from observations of the cosmos ought to correspond with revealed knowledge in Scripture for both “books” testify to the same God. And years of scientific research and biblical interpretation have generally borne out this truth.

Nevertheless, there are many theological truths, due both to their foundational character and to the clarity of the Scriptures testifying to them, that remain unchanged in the face of apparently contradictory scientific evidence. So it is that Jesus’s resurrection remains the cornerstone of Christian faith, even though no scientific theory would ever allow that dead men come back to life. In theological matters, then, Scripture remains as it were the primary book and where its contents are clear (as with the resurrection versus, for example, the “how” of creation), Christians must follow its lead. Thus, to recall our earlier example, while Pope John Paul II states that Christian faith is consistent with evolution, he also says that certain theories of evolution that remove God completely from the equation are to be rejected.

And this brings us back to the question of aliens and theology. For while the discovery of extra-terrestrial life poses no problem for the doctrine of creation, the same is not true in matters of Christology. Here again, many internet theologians see no difficulty; if God sent Jesus to earth as a human to save humans, they argue, why couldn’t God send him to Mars as a Martian to save Martians?

The motivation of this conclusion is understandable as it rightly expresses the depth of God’s love for his creation evident in the gospel story. Nevertheless, it represents a profound misunderstanding of the incarnation that stands at the heart of this story. The scriptural truth that “the Word became flesh” (John 1:14) does not mean that God took up flesh as an instrument only to lay it down again after the work was complete (implied by the conclusion that God could subsequently “become” an alien). Rather, it means that God becomes flesh by uniting his divinity to humanity in the one person of the Son (known theologically as the “hypostatic union”). While Jesus’s divine and human natures are unified so as to remain unmixed and unconfused, the hypostatic union teaches that Jesus’s divinity intimately touches every part of his humanity and vice versa. As a result of the incarnation, Jesus’s humanity is essential to who God is. Put differently, the glory of God is now seen in a human face (John 1:18, 2 Cor 4:6).

Scripturally, this deep union is indicated by his real birth from Mary, his recognizably personable actions throughout his life, his real death on a cross, and his resurrection and ascension back to the Father in the flesh. In the ascension, Jesus brings his human nature into the Godhead and thereby prepares the way for us to follow (John 14:2-3; 17:20-23). As such, Jesus cannot then become an alien to win aliens. Such a move would necessarily sever the hypostatic union and call into question human salvation for the salvific way into the nature of God would be blocked.

By way of conclusion, it is worth noting for my fellow E.T. enthusiasts, that aliens, should they exist, would not be without hope of salvation. By this model, they are, like all non-humans, a part of God’s good creation, which, having fallen in Adam, is restored to newness in the death and resurrection of the Messiah, even as Scripture and theology necessitate the identity of that Messiah be the unique and incomparable God-man.