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| Autori principali: | , , , , , , , , , |
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| Natura: | Preprint |
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2025
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| Soggetti: | |
| Accesso online: | https://arxiv.org/abs/2509.10611 |
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| _version_ | 1866908537469272064 |
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| author | Ranjan, Sukrit Wogan, Nicholas F. Glidden, Ana Wang, Jingyu Stevenson, Kevin B. Lewis, Nikole Koskinen, Tommi Seager, Sara Wakeford, Hannah R. van der Marel, Roeland P. |
| author_facet | Ranjan, Sukrit Wogan, Nicholas F. Glidden, Ana Wang, Jingyu Stevenson, Kevin B. Lewis, Nikole Koskinen, Tommi Seager, Sara Wakeford, Hannah R. van der Marel, Roeland P. |
| contents | The James Webb Space Telescope (JWST) has begun to spectrally characterize small exoplanets orbiting M-dwarf stars, but interpretation of these spectra is ambiguous, with stellar, instrumental, or atmospheric origins possible for apparent spectral features. Consequently, interpretation of JWST small exoplanet spectra follows a Bayesian approach, with less theoretically plausible interpretations facing a higher burden of proof. Here, we use photochemical modeling to evaluate the plausibility of warm exo-Titans, exoplanets with N$_2$-CH$_4$ atmospheres analogous to Titan but orbiting closer to their host stars. Consideration of warm exo-Titans is motivated by arguments from planet formation, as well as tentative evidence from observations. Using TRAPPIST-1e as a case study, we show that the higher instellation experienced by warm exo-Titans reduces their CH$_4$ lifetime $τ_{\text{CH}_{4}}$ relative to true Titan by orders of magnitude, reducing the probability of observing them. We constrain the $τ_{\text{CH}_{4}}$ on a warm exo-Titan to be $\leq0.1\times$ (and most likely $\leq0.02\times$) true Titan, implying the absolute probability of detecting a warm exo-Titan is $<0.1$ and likely $<0.01$. This finding is consistent with recent JWST nondetections of CH$_4$-dominated atmospheres on warm terrestrial exoplanets. The low prior probability means that the standard of proof required to claim a warm exo-Titan detection is high, and we offer specific suggestions towards such a standard of proof. Observation of oxidized carbon species would corroborate a putative warm exo-Titan detection. Confirmed detection of warm exo-Titans would signal the need to fundamentally rethink our understanding of the structure, dynamics, and photochemistry of Titan-like worlds. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_10611 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The Photochemical Plausibility of Warm Exo-Titans Orbiting M-Dwarf Stars Ranjan, Sukrit Wogan, Nicholas F. Glidden, Ana Wang, Jingyu Stevenson, Kevin B. Lewis, Nikole Koskinen, Tommi Seager, Sara Wakeford, Hannah R. van der Marel, Roeland P. Earth and Planetary Astrophysics The James Webb Space Telescope (JWST) has begun to spectrally characterize small exoplanets orbiting M-dwarf stars, but interpretation of these spectra is ambiguous, with stellar, instrumental, or atmospheric origins possible for apparent spectral features. Consequently, interpretation of JWST small exoplanet spectra follows a Bayesian approach, with less theoretically plausible interpretations facing a higher burden of proof. Here, we use photochemical modeling to evaluate the plausibility of warm exo-Titans, exoplanets with N$_2$-CH$_4$ atmospheres analogous to Titan but orbiting closer to their host stars. Consideration of warm exo-Titans is motivated by arguments from planet formation, as well as tentative evidence from observations. Using TRAPPIST-1e as a case study, we show that the higher instellation experienced by warm exo-Titans reduces their CH$_4$ lifetime $τ_{\text{CH}_{4}}$ relative to true Titan by orders of magnitude, reducing the probability of observing them. We constrain the $τ_{\text{CH}_{4}}$ on a warm exo-Titan to be $\leq0.1\times$ (and most likely $\leq0.02\times$) true Titan, implying the absolute probability of detecting a warm exo-Titan is $<0.1$ and likely $<0.01$. This finding is consistent with recent JWST nondetections of CH$_4$-dominated atmospheres on warm terrestrial exoplanets. The low prior probability means that the standard of proof required to claim a warm exo-Titan detection is high, and we offer specific suggestions towards such a standard of proof. Observation of oxidized carbon species would corroborate a putative warm exo-Titan detection. Confirmed detection of warm exo-Titans would signal the need to fundamentally rethink our understanding of the structure, dynamics, and photochemistry of Titan-like worlds. |
| title | The Photochemical Plausibility of Warm Exo-Titans Orbiting M-Dwarf Stars |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2509.10611 |