On April 17, it was announced with great fanfare that we were the closest yet to discovering exoplanetary life. Roughly 8.6 times larger than Earth and merely 120 light years away, exoplanet K2-18 b orbits a red dwarf star within the so-called Goldilocks zone for possible planetary life. Allegedly discovered through spectroscopic analysis, thanks to the James Webb telescope, were hints of two sulfur-based gases, which on Earth are produced only by microbial life. The conclusion was that K2-18 b is a “hycean world” (an ocean-covered world with a H2-rich atmosphere) possibly teeming with life.[1]
Not so fast. The response among fellow astrobiologists was sobering, largely dismissing the notion that any conclusive evidence had been found to suggest life exists on K2-18 b.[2] For those who remember (and I’m showing my age), the controversy surrounding K2-18 b was not unlike the one generated by ALH84001, otherwise known as the “Mars rock,” nearly thirty years ago. In August of 1996, it was announced in the journal Science, followed by a national press conference, that conclusive evidence for ancient fossils had been found in a meteorite from Mars.[3] That was also debunked.
Nevertheless, despite these false alarms, it remains easy (and thrilling) to imagine the high probability that life exists beyond Earth. Earth, after all, is a mere “pale blue dot” (to quote Carl Sagan) located in an ordinary galaxy consisting of at least a hundred billion stars in a universe populated by as many as two trillion galaxies. So how many stars? One estimate is 1024 stars, most of which have planets, with roughly one out of five of these planets hosting potentially habitable environments.[4] If life were truly absent in the universe beyond Earth, what a cosmic waste of space! (This is no judgment, just an observation.) And so the search continues. Since 1992, over 5,900 exoplanets have been discovered with many more undoubtedly to come.
It is often said that astrobiology is the only science that is in search of its subject, operating on faith (!) that life is somewhere out there in a near-infinite universe. Indeed, the search for exoplanetary life can easily carry a (pseudo-)religious impulse. Astrophysicist Paul Wallace observes, “There’s no scientific project more obviously religious than the search for extraterrestrial intelligence.”[5]
So what is astrobiology, this “faith-based” science? Officially, it is “the study of the origin, evolution, distribution, and future of life in the universe.”[6] Put simply, astrobiology is all about the cosmic drama of life, from its origin to its future. Drawing from a host of disciplines, astrobiology is the most far-reaching and multidisciplinary of the sciences, a growing coalition that includes astronomy, planetary science, geology, chemistry, and biology, as well as their many sub-disciplines. As such, astrobiology invites us to look at the “big picture,” the cosmos, as well as life down to its most fundamental constituents. This dual focus on the macro and the micro testifies to astrobiology’s comprehensive reach and integrative scope. And like theology, it is governed by big questions. According to the “NASA Astrobiology Strategy 2015” roadmap, three basic questions drive astrobiological research: 1) How does life begin and evolve? 2) Does life exist elsewhere in the universe? 3) What is the future of life on Earth and beyond?[7] Corollary questions include: What makes Earth habitable and inhabited? What are the requisite environmental conditions for life to begin, as well as to evolve in complexity? Is life a planetary phenomenon?
Is astrobiology the only faith-based science?
All to say, it is unfair to claim that astrobiology lacks a subject matter. There is plenty at hand for astrobiologists to study. But there is one limitation. In the words of David Grinspoon, “We are seeking to find something that we cannot fully define until after we have found it. Since we have only one example of life to inspect, we cannot – and should not – agree completely on a definition.”[8] While searching for life that we do not know, astrobiology can only begin with life as we know it – earth-bound life – as indicated, for example, by the following definition utilized by astrobiologists: life is “a bounded self-propagating chemical phenomenon that utilizes free energy to maintain and propagate itself and evolves by Darwinian evolution.”[9] Nevertheless, there’s always the chance that alien life is so alien that it is unrecognizable from such a lens.
Admittedly, “life as we know it” can be quite alien, given certain borderline cases. If life is limited to entities that can propagate, then what about mules? Viruses, in turn, cannot reproduce on their own but must hijack a living cell to do so. Add to that the “extremophiles” thriving on and in this planet, and you have quite an “alien” planet Earth. (I nominate the tardigrade as Earth’s mascot of resilience!) Yet we have no idea what kind of life might exist beyond our planet. Is it carbon-based or, perhaps, silicon-based? Does alien life require H2O or some other liquid medium? In astrobiology, such questions are fundamental. And they are also fun.
But there is one thing that many astrobiologists are counting on: that life, however alien, is a planetary phenomenon. That is, life does not simply exist “on” Earth, as if the planet were a mere stage on which the drama of life unfolds. Life does not exist simply in one corner of a planetary landscape. No, life exists in, with, by, through, and perhaps even “for” the planet. Life “as we know it” has permeated our planet, shaping it, as much as the planet has shaped life, all in co-evolutionary partnership. Life, in short, is planet changing. It is this assumption that drives the search for biosignatures reflected in an alien planet’s atmosphere, signs that deviate from chemical equilibrium and show up spectroscopically. Such is “the cornerstone of NASA’s current plans for searching for” exoplanetary life.[10]
Life is a planetary phenomenon
So what does a biblical scholar find theologically intriguing about astrobiology? If life proves to be abundant in the universe, then we must reckon with not one genesis but multiple “geneses.” God has a preferential option for life, including life’s diversity. If the cosmic abundance of life suggests to you that life on Earth lacks its specialness, think again. While life on Earth may lose its uniqueness, its intrinsic worth and ravishing beauty are by no means diminished in God’s sight (Psalms 104:24; 147:4). On the other hand, it is always good to receive a heavy dose of humility in knowing that we are not the only “game in town” in the universe.
And speaking of what is good for us, astrobiology (via a thought experiment) has something profound to say on the topic of sin. It begins with “Fermi’s Paradox.” In the summer of 1950, the Italian-American physicist Enrico Fermi asked his fellow physicists at Los Alamos in a casual conversation about UFOs, “Where is everybody?” Why hasn’t there been any evidence of alien life in the face of high probability? Attempts to resolve the paradox have been many, but the one that I find the most intriguing is so-called the “Great Filter.”[11]
One version of the great “Great Filter” hypothesis posits that many civilizations have in fact developed throughout the course of cosmic evolution. But many have collapsed, having failed to successfully pass through the “filter” that tests a civilization’s integrity and resilience – a cosmic rite of passage, as it were. The universe may very well be littered with dead “intelligent” species. Only a few, if any, have survived. When a civilization has developed, for example, the technology to extract and burn fossil fuels, master nuclear fusion, and develop AI, such advances also increase the civilization’s chances of self-destruction. With every new technological development comes the risk of exploitation and weaponization, increasing the chances of self-annihilation. Many of these dangers are the result of the human tendency to turn within and, conversely, turn against the other. Greed and domination are but two examples. Enough said.
Whether real or not, the Great Filter is an apt metaphor for the reality of sin and judgment writ cosmically. Call it “Calvin’s Cosmos.” Will Earth be just one more failed life experiment, failure due to “human depravity”? Or will a righteous “remnant” survive? Time will tell. In any case, I am grateful that astrobiology can frame the issue of sin in such a cosmic and urgent way. “In the deepest sense, the search for extraterrestrial intelligence is a search for ourselves,” Carl Sagan famously intoned.[12] And, I would add, that search is also a search for our best collective selves. This is just one way that astrobiology, in its reach for the stars, hits home.
[1] Nikku Madhusudhan, et al, “New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI,” The Astrophysical Journal Letters 983, 2 (17 April 2025): 1-21. https://iopscience.iop.org/article/10.3847/2041-8213/adc1c8
[2] See, e.g., Luis Welbanks, et al, “The Challenges of Detecting Gases in Exoplanet Atmospheres.” Astrophysics. Submitted for peer review. https://arxiv.org/abs/2504.21788
[3] David McKay, et al. “Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001,” Science, 273, no. 5277 (August 16, 1996): 924-30.
[4] David Grinspoon, “Life as a Planetary Phenomenon: A Planetary Scientist’s Perspective,” in Astrobiology, Religion, and Society: Considering Life on a Planetary Scale, eds. Frederick Simmons, William Storrar, and Edwin Turner (Cambridge: Cambridge University Press, forthcoming).
[5] Paul Wallace, Stars Beneath Us: Finding God in the Evolving Cosmos (Minneapolis, MN: Fortress, 2015), 139.
[6] National Academies of Sciences, Engineering, and Medicine, An Astrobiology Strategy for the Search for Life in the Universe (Washington DC: National Academies Press, 2019), 1.
[7] For the full document, see https://astrobiology.nasa.gov/uploads/filer_public/01/28/01283266-e401-4dcb-8e05-3918b21edb79/nasa_astrobiology_strategy_2015_151008.pdf
[8] Grinspoon, “Life as a Planetary Phenomenon.”
[9] Grinspoon, “Life as a Planetary Phenomenon.”
[10] Grinspoon, “Life as a Planetary Phenomenon.”
[11] For a recent exposition, see Jonathan H. Jiang, Philip E. Rosen, Kelly Lu, Kristen A. Fahy, Piotr Obacz, “Avoiding the ‘Great Filter’: Extraterrestrial Life and Humanity’s Future in the Universe,” Journal of Humanities & Social Sciences 6, 2 (2023): 59-66. https://arxiv.org/abs/2210.10582
[12] Sagan, Carl. 1979. Broca’s Brain: Reflections on the Romance of Science. New York: Random House, 314-15.
