Artists light-hearted impression of life on K2-18b.
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The day long anticipated by those who understand both science and theology may finally have arrived. Scientists have detected—with a 99.7% probability—the unmistakable signs of life on the distant exoplanet K2-18b.
Although this degree of certainty doesn't yet satisfy the rigorous standards of science, which typically require a confidence level of greater than 99.99994%, researchers anticipate surpassing that threshold within the next 16 to 24 hours (as of this article's publication).
The theological implications of this discovery are profound. If confirmed, as now seems highly likely, it would indicate that Earth is not unique as a cradle of life, directly challenging biblical narratives which position Earth exclusively as the divinely chosen habitat for humanity. The Bible remains thoroughly anthropocentric and geocentric, offering no indication that life or divine creation occurred elsewhere in the comparatively small and flat universe it describes.
For creationists, this finding significantly undermines their long-standing argument—summarised by the simplistic slogan, "You can't get life from non-life"—which claims life could only arise through divine intervention. The presence of life on K2-18b demonstrates that life can indeed emerge naturally under the right conditions, suggesting such events may be far more common across the universe than creationist arguments would allow. Indeed, with potentially trillions of planets sharing Earth-like conditions, life may not only be possible but prevalent.
This discovery also challenges creationist claims about Earth's position in the so-called 'Goldilocks zone'. Creationists frequently argue that Earth's precise placement around the Sun proves divine intent. However, the existence of life-supporting conditions on K2-18b shows that such habitable zones are not rare, singular phenomena but commonplace, existing around countless other stars across the cosmos.
The discovery, by astronomers, led by the University of Cambridge, using data from the James Webb Space Telescope (JWST), is the subject of an open access paper in The Astrophysical Journal Letters and is described in a Cambridge University press release by Sarah Collins:
What information do you have on the location and distance from Earth of the exoplanet K2-18 b? K2-18b is an exoplanet situated approximately 124 light-years from Earth in the constellation Leo. It orbits a red dwarf star known as K2-18, which is cooler and smaller than our Sun. The planet resides within its star's habitable zone, a region where conditions might allow for the presence of liquid water on the planet's surface.
Discovered in 2015 by NASA's Kepler Space Telescope during its K2 mission, K2-18b has garnered significant interest due to its potential to support life. Recent observations using the James Webb Space Telescope have detected molecules such as methane and carbon dioxide in its atmosphere, along with possible traces of dimethyl sulfide (DMS). On Earth, DMS is predominantly produced by marine phytoplankton, making its presence a potential biosignature. However, scientists emphasize the need for further observations to confirm these findings and rule out non-biological sources.
K2-18b is classified as a "Hycean" planet—a term describing worlds with hydrogen-rich atmospheres and vast oceans. It is about 8.6 times more massive and 2.6 times larger in radius than Earth, placing it between Earth and Neptune in size. The planet completes an orbit around its star every 33 days.
While the discovery of potential biosignatures on K2-18b is intriguing, researchers caution that more data is needed to determine the planet's habitability and the true nature of its atmospheric components.
Is it in the Milky Way galaxy?
Yes, K2-18b is located within the Milky Way galaxy. In fact, all exoplanets discovered so far—including K2-18b—reside within our own galaxy. The Milky Way spans around 100,000 light-years in diameter, and K2-18b, at approximately 124 light-years away, is relatively close in cosmic terms. It's situated in the constellation Leo, which is easily visible from Earth during certain times of the year. To date, no exoplanets have been discovered beyond the Milky Way, as the distances and observational limitations make detecting planets in other galaxies extraordinarily difficult with current technology.
Strongest hints yet of biological activity outside the solar system
Astronomers have detected the most promising signs yet of a possible biosignature outside the solar system, although they remain cautious.
Using data from the James Webb Space Telescope (JWST), the astronomers, led by the University of Cambridge, have detected the chemical fingerprints of dimethyl sulfide (DMS) and/or dimethyl disulfide (DMDS), in the atmosphere of the exoplanet K2-18b, which orbits its star in the habitable zone.
On Earth, DMS and DMDS are only produced by life, primarily microbial life such as marine phytoplankton. While an unknown chemical process may be the source of these molecules in K2-18b’s atmosphere, the results are the strongest evidence yet that life may exist on a planet outside our solar system.
The observations have reached the ‘three-sigma’ level of statistical significance – meaning there is a 0.3% probability that they occurred by chance. To reach the accepted classification for scientific discovery, the observations would have to cross the five-sigma threshold, meaning there would be below a 0.00006% probability they occurred by chance.
The researchers say between 16 and 24 hours of follow-up observation time with JWST may help them reach the all-important five-sigma significance. Their results are reported in The Astrophysical Journal Letters.
AbstractA predictable creationist response to this news will likely be the claim that it merely proves a creator god is capable of creating life on other planets too, since, so they will argue, it still doesn’t explain how life could have emerged from non-life there either.
The sub-Neptune frontier has opened a new window into the rich diversity of planetary environments beyond the solar system. The possibility of hycean worlds, with planet-wide oceans and H2-rich atmospheres, significantly expands and accelerates the search for habitable environments elsewhere. Recent JWST transmission spectroscopy of the candidate hycean world K2-18 b in the near-infrared led to the first detections of the carbon-bearing molecules CH4 and CO2 in its atmosphere, with a composition consistent with predictions for hycean conditions. The observations also provided a tentative hint of dimethyl sulfide (DMS), a possible biosignature gas, but the inference was of low statistical significance. We report a mid-infrared transmission spectrum of K2-18 b obtained using the JWST MIRI LRS instrument in the ∼6–12 μm range. The spectrum shows distinct features and is inconsistent with a featureless spectrum at 3.4σ significance compared to our canonical model. We find that the spectrum cannot be explained by most molecules predicted for K2-18 b, with the exception of DMS and dimethyl disulfide (DMDS), also a potential biosignature gas. We report new independent evidence for DMS and/or DMDS in the atmosphere at 3σ significance, with high abundance (≳10 ppmv) of at least one of the two molecules. More observations are needed to increase the robustness of the findings and resolve the degeneracy between DMS and DMDS. The results also highlight the need for additional experimental and theoretical work to determine accurate cross sections of important biosignature gases and identify potential abiotic sources. We discuss the implications of the present findings for the possibility of biological activity on K2-18 b.
1. Introduction
The discoveries of temperate exoplanets orbiting nearby stars and the advent of the James Webb Space Telescope (JWST; J. P. Gardner et al. 2006) are opening up the possibility of detecting biosignatures on habitable exoplanets. While habitable exoplanets orbiting Sun-like stars are still beyond the reach of JWST, such planets orbiting smaller M dwarf stars are within the range of observability with JWST. A number of low-mass exoplanets orbiting M dwarfs have been observed in recent years, highlighting their diversity and both the challenges of and opportunities in characterizing their atmospheres with JWST (e.g., O. Lim et al. 2023; N. Madhusudhan et al. 2023.1b; E. M. May et al. 2023.2; S. E. Moran et al. 2023.3; L. Alderson et al. 2024; B. Benneke et al. 2024.1; M. Damiano et al. 2024.2; N. Scarsdale et al. 2024.3; M. Holmberg & N. Madhusudhan 2024.4; N. L. Wallack et al. 2024.5; M. K. Alam et al. 2025).
The Hycean paradigm developed in recent years has the potential to significantly expand and accelerate the search for life elsewhere (N. Madhusudhan et al. 2021). Hycean worlds are planets with habitable ocean-covered surfaces and H2-rich atmospheres. Their lower densities, larger sizes, and lighter atmospheres compared to Earth-like planets make hycean worlds more readily detectable and more conducive for atmospheric characterization. Similarly, their wider habitable zone compared to Earth-like planets also makes them more abundant, with over a dozen hycean candidates already identified (e.g., N. Madhusudhan et al. 2021; A. Fukui et al. 2022; K. Kawauchi et al. 2022.1; T. Mikal-Evans et al. 2023.4; C. Piaulet et al. 2023.5).
Early observations with JWST have bolstered the promise of this new avenue, starting with the candidate hycean world K2-18 b. The planet has a mass of 8.63 ± 1.35 M⊕ and a radius of 2.61 ± 0.09 R⊕ (B. Benneke et al. 2019; R. Cloutier et al. 2019.1), and it orbits in the habitable zone of an M2.5V star (B. T. Montet et al. 2015; R. Cloutier et al. 2017; P. Sarkis et al. 2018). The bulk parameters of the planet are consistent with a degenerate set of internal structures, including a hycean world, a mini-Neptune or a gas dwarf, i.e., a rocky planet with a thick H2-rich atmosphere (N. Madhusudhan et al. 2020). Atmospheric observations are key to breaking the degeneracy.
A transmission spectrum of K2-18 b obtained with the Hubble Space Telescope WFC3/G141 spectrograph (1.1–1.7 μm) was initially used to infer the presence of water vapor (H2O) in its atmosphere (B. Benneke et al. 2019; A. Tsiaras et al. 2019.2; N. Madhusudhan et al. 2020). However, significant degeneracies were found between potential absorption due to H2O and that due to methane (CH4; B. Bézard et al. 2022.2; D. Blain et al. 2021.1) or contributions from stellar heterogeneities (T. Barclay et al. 2021.2). Transmission spectroscopy of K2-18 b with JWST led to the first detections of carbon-bearing molecules, CH4 and carbon dioxide (CO2), at 5σ and 3σ significance, respectively, in its H2-rich atmosphere (N. Madhusudhan et al. 2023.1b). The high sensitivity and wide wavelength range of the JWST spectrum helped resolve the previous CH4–H2O degeneracy, resulting in a strong detection of CH4 and nondetection of H2O. The nondetection of H2O was consistent with the low photospheric temperature retrieved, implying H2O condensation at the altitudes probed by the transmission spectrum (N. Madhusudhan et al. 2023.6a, 2023.1b).
The retrieved atmospheric composition of K2-18 b also provided important constraints on its internal structure. The detections of CH4 and CO2 at significant abundances, along with the nondetections of ammonia (NH3) and carbon monoxide (CO) and the overall high CO2/CO ratio, are consistent with prior predictions for a hycean atmosphere (R. Hu 2021.3; S.-M. Tsai et al. 2021.4; N. Madhusudhan et al. 2023.6a). Other scenarios requiring a deep H2-rich atmosphere, such as a mini-Neptune or a gas dwarf, as mentioned above, are inconsistent with the retrieved abundances (N. Madhusudhan et al. 2023.1b). For example, a mini-Neptune scenario (e.g., N. F. Wogan et al. 2024.6) is incompatible with most of the retrieved abundances, especially the low NH3 and high CO2/CO ratio (G. J. Cooke & N. Madhusudhan 2024.7; C. R. Glein 2024.8). Similarly, models considering NH3 depletion due to magma oceans (O. Shorttle et al. 2024.9) in the gas dwarf scenario were found to be inconsistent with mass and density constraints, among other factors, while also being inconsistent with the retrieved composition (F. E. Rigby et al. 2024.10). Therefore, presently, the atmospheric abundances of K2-18 b are best explained by a hycean world scenario and are incompatible with mini-Neptune or gas dwarf scenarios requiring a deep H2-rich atmosphere.
Open questions remain as to the possibility of habitable conditions on K2-18 b. While the atmospheric composition is consistent with predictions for hycean conditions (N. Madhusudhan et al. 2023.1b) and a large water inventory in the interior (C. N. Luu et al. 2024.11; J. Yang & R. Hu 2024.12), the nature of the possible ocean beneath the H2-rich atmosphere is unknown. A habitable liquid water ocean requires an adequate albedo (AB) due to clouds/hazes (A. A. A. Piette & N. Madhusudhan 2020.1; N. Madhusudhan et al. 2021), with the latest theoretical estimate of the required albedo being AB > 0.5–0.6 (J. Leconte et al. 2024.13), similar to that assumed for candidate hycean worlds (N. Madhusudhan et al. 2021). A cloud-/haze-free atmosphere would render the surface too hot to be habitable and/or have water in a supercritical state (N. Madhusudhan et al. 2020; A. A. A. Piette & N. Madhusudhan 2020; M. Scheucher et al. 2020.2; H. Innes et al. 2023.7; R. T. Pierrehumbert 2023.8; J. Leconte et al. 2024.13). While the required albedo may be consistent with the evidence for clouds/hazes reported at the day–night terminator of K2-18 b (N. Madhusudhan et al. 2023.1b), and is within the range of AB of 0.3–0.8 known for atmospheres of most solar system planets, the dayside albedo of K2-18 b has not been measured directly.
On the other hand, recent studies have also indicated the potential for biotic conditions on K2-18 b. The CH4 on K2-18 b may be contributed, partly or predominantly, from biogenic sources, similar to CH4 from methanogenic bacteria on Earth (N. Madhusudhan et al. 2023.6a, 2023.1b; G. J. Cooke & N. Madhusudhan 2024.7; N. F. Wogan et al. 2024.6). In particular, the detection of abundant CH4 alongside CO2 in a shallow H2-rich atmosphere is more easily explained by an inhabited hycean scenario than an uninhabited case (G. J. Cooke & N. Madhusudhan 2024.7; N. F. Wogan et al. 2024.6). The CH4–CO2 pair has also been proposed as a promising biosignature for Earth-like habitable exoplanets, as may have been the case for the early Earth (J. Krissansen-Totton et al. 2018.1). However, the prospect of abiotically produced CH4 through atmospheric chemistry cannot be ruled out in the uninhabited hycean scenario for K2-18 b (G. J. Cooke & N. Madhusudhan 2024.7). Another potential indication of biological activity was suggested by a weak (≲2σ) inference of dimethyl sulfide (DMS) in K2-18 b with previous JWST observations (N. Madhusudhan et al. 2023.1b).
The tentative inference of DMS in K2-18 b opens an important debate as to the possible presence of life on K2-18 b. On the one hand, the low detection significance highlights the challenges in detecting such molecules. In the case of the previous JWST observations of K2-18 b, the detection significance of DMS depended on the relative offsets between the spectra observed from different detectors on the JWST NIRISS and NIRSpec instruments, ranging from 2.4σ with no offsets to below 1σ for two offsets (N. Madhusudhan et al. 2023.1b). Another challenge is the strong degeneracy between the spectral features of DMS near 3.3 μm and 4.3 μm with strong features of CH4 and CO2 at overlapping wavelengths, as well as potential contributions from other hydrocarbons with strong features in the 3–5 μm range (N. Madhusudhan et al. 2023.1b; S.-M. Tsai et al. 2024.14). On the other hand, a confident detection of a molecule like DMS would serve as a more robust biosignature than molecules like CH4, which are more easily detectable but may be present in abundance through abiotic chemistry.
The robustness of DMS as a biosignature in H2-rich environments has been proposed extensively in the literature both for rocky planets (S. D. Domagal-Goldman et al. 2011; S. Seager et al. 2013a; D. C. Catling et al. 2018.2; E. W. Schwieterman et al. 2018.3) and hycean worlds (N. Madhusudhan et al. 2021). Despite the low detection significance, the reported abundance constraints of DMS are physically plausible for realistic levels of biogenic sources (N. Madhusudhan et al. 2023.1b; S.-M. Tsai et al. 2024.14). In particular, DMS mixing ratios as high as 10−2 are possible in K2-18 b for high biogenic fluxes of sulfur-based biosignature gases above ∼20 times Earth levels (S.-M. Tsai et al. 2024.14).
In this work, we conduct an independent search for molecular species, including DMS, in K2-18 b in a different wavelength range, using the JWST MIRI spectrograph. As discussed above, the previous tentative inference of DMS in K2-18 b was made using a near-infrared transmission spectrum in the 1–5 μm range obtained with the JWST NIRISS and NIRSpec instruments. However, the evidence for DMS was affected by potential flux offsets between the different detectors (N. Madhusudhan et al. 2023.1b). Therefore, an independent search for DMS and other such molecules using a different instrument in a complementary spectral range is invaluable for assessing the significance of prior findings and for providing an independent line of evidence. Mid-infrared spectroscopy with JWST provides a promising avenue in this direction. In addition to providing a complementary spectral window (∼5–12 μm) to previous observations, this wavelength range also encompasses strong spectral features of DMS and several other biosignature gases (S. D. Domagal-Goldman et al. 2011; S. Seager et al. 2013.1b; E. W. Schwieterman et al. 2018.3; S.-M. Tsai et al. 2024.14).
We present a mid-infrared transmission spectrum of K2-18 b with JWST, the first for a habitable-zone exoplanet. This allows for an independent search for DMS and other biosignature gases in the atmosphere of K2-18 b, as discussed above. In what follows, we present our observations, data reduction, and light-curve analyses in Section 2. We discuss our retrieval approach and present the atmospheric inferences obtained from the transmission spectrum in Section 3. We summarize our results and discuss the implications in Section 4.
Nikku Madhusudhan, Savvas Constantinou, Måns Holmberg, Subhajit Sarkar, Anjali A. A. Piette, & Julianne I. Moses
New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI
The Astrophysical Journal Letters 983(2); DOI: 10.3847/2041-8213/adc1c8.
Copyright: © 2025 The authors.
Published by the American Astronomical Society. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
However, few creationists seem to grasp the fundamentals of their own theology. The broader implications — that the Bible clearly presents Earth as the uniquely created home of humanity, the special focus of divine creation — will likely be lost on them. Equally overlooked will be the theological consequences for doctrines centred on salvation exclusively through Jesus, who, according to Christian belief, was incarnated on Earth specifically to redeem humankind. If intelligent life exists elsewhere, does it require salvation too? If so, was there a parallel incarnation on K2-18b?
The deeper issue for creationism, though, is the collapse of one of its favourite arguments: that the emergence of life from inorganic matter is so staggeringly improbable on Earth as to be effectively impossible — thus requiring divine intervention. The discovery of life elsewhere in the universe severely undermines that claim. It strongly suggests that, far from being a miraculous exception, life is a natural outcome where the conditions are right. Rather than reinforcing the need for a supernatural explanation, this finding points to the probability that life is a common feature of the cosmos — not a divine anomaly.
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