Billions of stars populate the galaxies of our universe. Are there planets beyond our solar system as well? What may appear quite plausible now had only been a hypothesis until about twenty years ago. Then, on October 5, 1995, two Swiss astronomers, Michel Mayor and Didier Queloz of the Geneva Observatory, announced “the presence of a Jupiter‐mass companion to the star 51 Pegasi” (Mayor and Queloz , 355), apparently circling its star in only four days.

Mayor and Queloz's discovery of the first planet exterior to our solar system which was circling a sun‐like star at first elicited skepticism. Discoveries like this for too long had been swiftly disproven (Weintraub , 43–50). Also, the features of the discovered planet did not match the expectations for planetary locations, drawn from the structure of our solar system. Yet the claim of Mayor and Queloz did hold. Today, we know that the “most remarkable result from the discovery of exoplanets is their variety” (Smith , 504). More than 2,000 such “exoplanets” are confirmed. There will be likely millions more, as one can expect at least every tenth distant sun to be surrounded by a planet (Batalha ); other estimates include at least one planet on average per star (Wilkinson , 419). In this case, and if 25 percent of sun‐like stars have an Earth‐sized planet in a habitable zone, there could be over 10 billion potentially habitable earths in our galaxy (Wilkinson , 420). There are at least about 300 billion stars in our galaxy alone, and billions of galaxies out there (Gribbin , 28–29).

These exoplanets are just a bit hard to find, as they do not shine. How they can be found nevertheless, astronomer and theologian David Wilkinson explains in his article in this issue.

The search for exoplanets is driven by interest in the “habitable” ones among them, those that are a suitable distance from their star allowing for liquid water, for instance. Could such a planet one day in the far future provide resources or even shelter for humankind? Will we find one day a habitable planet that is even inhabited? These kinds of questions drive the public interest in the subject. Coupled with the natural curiosity of the scientists, they further the research agenda. In his contribution to this section, David Wilkinson warns against too hastily equating “Earth‐like planets to habitable Earth‐like planets and then to inhabited Earth‐like planets and then to inhabited by intelligent beings Earth‐like planets” (Wilkinson , 421) We should keep Fermi's paradox in mind: If intelligent life really is abundant in the universe, “where is everybody?” (Webb ).

Interestingly, the idea of alien intelligent life in the universe is not at all a new invention. Already the early Greek atomists expected “life out there” in an infinite cosmos (Crowe and Dowd , 5). A revival of this idea of “many worlds” occurred when the Copernican revolution shattered Aristotelian and Ptolemaic geocentrism. Michael Crowe has described the history of the extraterrestrial life debate from antiquity until recent years in an earlier issue of Zygon: Journal of Religion and Science (Crowe ). A rough sketch of the developments can also be found in Michael Crowe's contribution to this section.

What is important to remember is that there were two principles supporting the idea of a plurality of inhabited worlds in the universe: (1) the Copernican principle, according to which “there is nothing special about our region of space. This implied that other regions must share with Earth the presence of intelligent beings” (Crowe , 432); and (2) the principle of plenitude: the more life in the universe the greater the glory of God, it assumed, because God “would not waste the efforts involved in producing the universe without placing within it widespread ETI [extraterrestrial intelligence]” (Crowe , 433). So there most likely had to be life everywhere, as “the heavens declare the glory of God” (Psalm 19:1).

It hence may not surprise the reader that even Immanuel Kant was an adherent of the idea of a plurality of inhabited worlds, and remained so even in his critical phase (Szendy , 43–79; Losch ). David Dunér provides an in‐depth study of the thought of his contemporary speculative counterpart, Emanuel Swedenborg, who had a scientific past, and tried to reconcile the science of his time—including the belief in extraterrestrials—with spirituality and theology. Swedenborg also claimed to have talked to the extraterrestrials in person, by means of his spiritual journeys, a stance Kant deliberately tried to distance himself from (e.g., Kant ). In any case, Swedenborg's attitude allows for a glimpse into eighteenth‐century belief in extraterrestrial life and gives us a taste of that century's thought.

The degree to which belief in ETI had permeated public awareness in the first half of the nineteenth century is indicated by an event that occurred in 1835, called today “the Great Moon Hoax.” A series of newspaper articles suggested that prominent astronomer Sir John Herschel had telescopically detected intelligent beings on the Moon. Although nearly everyone believed the reports (Crowe , 438), it was only fiction. The popularity of the discussion testifies to how widespread the belief in extraterrestrial life was. Likewise, Percival Lowell's “observation” of canals on Mars sustained the belief (Smith , 499).

The expectations of  ETI changed in the course of the nineteenth century, mostly due to the findings of one person, William Whewell. According to Michael Crowe's contribution to this section prominent scientists like Sir William Herschel before Whewell did not hesitate to speculate about life even on the Sun (Crowe , 434). Whewell demurred. His application of the inverse square law and his knowledge of geology led him to believe that large areas of the sky have to be devoid of population. His motivation may have been religious (“The earth…cannot, in the eyes of any one who accepts this Christian faith, be regarded as being on a level with any other domiciles”; Whewell , 44), yet by questioning the principle of plenitude and the argument from design he almost paved the way for Darwinian findings (Whewell , 210–47). One could add at least partial credit for this innovation to Michael Crowe's most elaborate and thoughtful reconstruction of Whewell's thought in this issue.

One of the books popularizing the idea of a plurality of habitable worlds was William Derham's Astro‐Theology (Derham ), which saw many editions worldwide. His “astro‐theology” was one application of the more general idea of a physico‐theology, meaning that “the wonderful and astonishing order and efficiency we can see in nature, the countless life forms we can find on Earth, show that there must be an omnipotent and infinitely wise Creator” (Dunér , 454) Derham himself also authored a more general Physico‐Theology (Derham ), yet the objections of Hume and Kant make such a belief today superfluous, although it is true, as Kant noted, that such a creed indeed “enlivens the study of nature” (Kant , 579).

When Ted Peters called for an establishment of the field of “astrotheology” (Peters ), he was certainly thinking less of these ancient attempts than of coining the word analogously to the emerging field of astrobiology. There had been a previous field called exobiology—the study of extraterrestrial life forms—but due to the lack of findings, one enlarged the field to encompass the only life we know of until today. Likewise, most theological researchers have followed in calling their theological interpretations of the astrobiological expectations “astrotheology” instead of “exotheology.”

For the theologian, the sheer possibility of intelligent life beyond our planet carries implications which need a good deal of theological reflection. David Wilkinson picks up on these in the second part of his essay, clarifying that, although the recent discoveries emphasize the extravagance of a Creator God, “Christian theology will resist any attempt to resurrect any design argument on the basis of exoplanet discoveries” (Wilkinson , 424). Nevertheless, acknowledging the great diversity of creation “means that it is to be respected and cared for as a gift” (Wilkinson , 423)

Ted Peters in his article explores the field of “astrochristology,” thereby listening to the choir of theological voices emphasizing the compatibility of modern Christian religious beliefs and astrobiological expectations. Against Thomas Paine's old (and often repeated) assumption that “to believe God created a plurality of worlds … renders the Christian system of faith at once little and ridiculous, and scatters it in the mind like feathers in the air” (Paine , 84), the contributors to this kind of concert make a compatibility of Christianity with the idea of a plurality of worlds appear sound. Two crucial issues have to be dealt with: if there is intelligent extraterrestrial life on exoplanets, should Christians expect multiple incarnations or simply one on Earth? And, more fundamentally, why is there an incarnation in the first place? Is it simply a sign of divine self‐communication or is it needed to fix a broken creation? These questions entail considerations of anthropocentrism and geocentrism. Was it relevant that Christ had become human? Did he also become an extraterrestrial fellow being? Peters claims, following biblical resources, a universality of the Christ event, without denying the possibility of other divine self‐revelation “that could take place anywhere at any time” (Peters , 494).

Will astrobiology and astrotheology result in the decentering of humanity in cosmic dimensions? (cf. Drees , 69) Maybe they could result in changing our life‐value narratives, as Lucas Mix argues. Although he follows Hume in his traditional “is” and “ought” divide, he also believes that “the empirical ground affects our morality, even though it does not fully determine it” (Mix , 520). Mix employs the metaphor of seeds and soil (the narratives that grow out of fundamental ethical convictions) to develop his thoughts. He describes two dominant yet divergent tropes, the Pale Blue Dot trope—who are we, what is Earth in the vastness of the universe?—and the Anthropocene trope—we are living in the age of humans who change the face of our planet, which sets us apart from other life. The two tropes have both been used to support holistic life‐value narratives over hierarchical narratives “with Christian theology set up as the opposition” (Mix , 524). Nevertheless, scriptural witness demonstrates a plurality of life‐value narratives. Mix's conclusion is that “the Hierarchical and Holistic Narratives provide a way to think about the relative value of biological and human life within the cosmos, and provide tools for analyzing both seeds and soil as we cultivate new ethical paradigms” (Mix , 529)

In his former survey article (Peters , 447), Ted Peters already mentioned the different branches of astroethics that need to be discussed, be it (1) astroethics for microbiological life in our solar ghetto, like (a) planetary protection, (b) space debris, (c) satellite surveillance, (d) scientific privilege vs. space profit, or (e) weaponization of space, or (2) astroethics for intelligent life in the larger Milky Way metropolis. What is in my view missing from the list is the more fundamental level Mix touches upon. What is life? Which value does human life possess in cosmic dimensions? Who can say? “Where does the ought come from?,” as Margaret Race (SETI Institute) put it during an astrotheology workshop held at the CTNS Berkeley in June 2015. The papers presented at the workshop are most likely published in the journal Theology and Science. There have been further events in the framework of the International Society for Science and Religion's (ISSR's) meetings at the AAR in 2013, resulting in a compilation on astrotheology soon to be published (Peters et al. forthcoming).

The European Society for the Study of Science and Theology (ESSSAT) also recently took up questions touching astrobiological questions in their biannual conferences, asking “Are we special?” in 2016, and (earlier) “What is life?” in 2012 (Evers et al. ). In addition, the field of astrobiology itself is open for contributions from the humanities and from theology. The Center for Space and Habitability (CSH) in Bern, Switzerland, hired a theologian and started a project with theology, “Life Beyond Our Planet?” (). Note the question mark at the end of the project's title, which an Internet address unfortunately cannot contain. The first fruit of this project has been another conference on “What is Life?,” resulting in a book involving science, philosophy, and theology (Losch forthcoming). Also a volume in Cambridge University Press's astrobiology series showed the openness and need for ethical and theological considerations within the field (Bertka ). Oxford University Press is not idle either, having important titles like David Catling's “Very Short Introduction” into astrobiology (Catling ) and David Wilkinson's Science, Religion and the Search for Extraterrestrial Intelligence in their program (Wilkinson ). With astrobiology taking more realistic ground with the discoveries of exoplanets, there are more and more books being published that reflect on the potential impact of extraterrestrial findings (e.g., Dunér et al. ; Hart ; Impey, Spitz, and Stoeger ; Vakoch ). Even the Royal Society dedicated one of its transactions to such a discussion (Dominik and Zarnecki ). The mentioned project at Bern is currently mapping the many contributions and establishing an Online Library on the topic, published on its website.

The Nordic Astrobiology Network dedicated one of its summer schools and several conferences to the contribution of the humanities, resulting in a forthcoming special issue of the International Journal of Astrobiology titled “The History and Philosophy of the Origin of Life,” guest edited by David Dunér, Christophe Malaterre, and Wolf Geppert. On the other side of the Atlantic, NASA is of course a highly important player and from early on has invited researchers from the humanities and theologians to contribute (Berendzen ). NASA's astrobiology program, conjointly with the Templeton Foundation, sponsors research fellowships at the Center for Theological Inquiry (CTI) in Princeton, opening an “Inquiry on the Societal Implications of Astrobiology.” NASA's chief historian, Steven J. Dick, who authored several books on the topic (Dick , ), was one of the pioneers in the field, others being Karl S. Guthke at Harvard (Guthke , English translation 1990) and Michael Crowe at Notre Dame. (His classic is of course Crowe ; a more recent source book is Crowe .) Dick and Crowe have exchanged their materials and worked together. A student of Crowe is Matthew Dowd (Notre Dame as well), who recently coedited with Douglas Vakoch from the SETI institute an extensive discussion of the famous equation by SETI pioneer Frank Drake (Vakoch and Dowd ). Finally, the Vatican Observatory has to be mentioned, which drew some media attention with questions like “Would You Baptize an Extraterrestrial?” (Consolmagno ).

This raises the question: What do religious people think about extraterrestrial life? Here, the “Peters ETI Religious Crisis Survey” has to be mentioned, which came to the conclusion that “religious persons, for the most part, do not fear contact. Forecasts regarding imminent collapse of Earth's religious belief systems were found to be more prevalent among nonreligious respondents than among religious respondents” (Peters and Froehling ). Although the data sample Peters rests his findings on could be bigger, the evidence for believers being less troubled with the possibility of extraterrestrial life seems strong.

Another effort to map the different religions’ stances on the topic is David A. Weintraub's Religions and Extraterrestrial Life (), which makes use of relevant religious literature. To grant the plurality of Earth's religions some ground, Howard Smith's article in our section in this issue of Zygon includes a Jewish perspective on astrotheology. According to traditional rabbinic interpretation, ETI is even included in the Biblical narrative. More important, Smith's stance is also a more skeptical (Smith himself would say “more realistic”) approach to the topic, employing the “misanthropic principle.” Relativity constraints on the speed of light and the fact of the universe's continuous expansion lead him to conclude: “We are probably alone, at least for all practical purposes” (Smith , 498) This would present of course a dilemma for religious believers, “who have spent centuries showing that Divine potency or grace should naturally imply many extraterrestrial civilizations, but who now must justify the need for the vast, excess cosmos beyond human reach” (Smith , 515) We should, however, rejoice in our good fortune. “Atheists and religious people alike can also identify in it an expression of pride in humanity” (Smith , 514). With it comes an ethical responsibility we have already spoken of.

Astrotheology is a rising field, yet for now it is not clear, if it—like astrobiology—has any other subject than Earthly life and religion. Many would say, at least, that due to the vastness of the universe with all its planets, it is very probable it has a broader basis. Yet this is still an issue of assumptions, hopes, and beliefs, maybe another reason besides the necessary ethical considerations why philosophy and theology are important dialogue partners for science. In this context, and especially regarding the mythical hope of alien salvation that drives the SETI institute (Peters , 19), theology should not forget its critical, prophetic function (Jackelén ) and remain sober and realistic. So the astrotheology of today is different than that of the eighteenth century and should include the possibility of a zero result. The problem is, however, that in cosmic dimensions it is difficult to verify something not being there. And then, maybe it is also a little too tempting for Earthly religion to stay anthropocentric and geocentric, so what sounds sober could also turn out to be biased as well.