Searching for Biosignatures on Transiting Habitable Planets with ELT/ANDES ✛ ✎ ✦
Context
Searching for biosignatures like oxygen and methane in the atmospheres of terrestrial exoplanets is one of modern astrophysics' grand quests. With the deployment of the 39-meter ELT and its high-resolution ANDES spectrograph (R~100,000), we now have a window into the atmospheres of potentially habitable worlds around red dwarfs. Transit method observations combined with high-resolution spectroscopy let us pick out faint molecular lines from the stellar glare, using the Doppler effect.
Methods
We ran numerical simulations of transmission spectra for 18 rocky exoplanets from the Habitable Worlds Catalog. For each, we built cloud-free, Earth-like atmospheres with a two-layer temperature profile and prescribed amounts of H2O, CO2, CH4, and O2. Equilibrium temperature was estimated from the Stefan–Boltzmann law under a blackbody approximation. Using the radiative transfer code petitRADTRANS, we produced high-resolution synthetic spectra and injected realistic noise based on the ANDES exposure time calculator. To assess significance, we performed a Bayesian analysis of the cross-correlation function with an AR(1) autoregressive model that accounts for correlations between adjacent Doppler shifts.
Results
Our analysis shows that water vapor is the easiest to detect: on TRAPPIST-1 planets, it can be firmly spotted in 10–19 transits, and on LHS 1140 b in 30. Carbon dioxide needs about 1.5 times more transits; methane, 3 times; and oxygen, 4 times compared to water. Out of the 18 planets studied, confident (log B ≥ 2) detection of at least one molecule in under 100 transits is possible for eight, with TRAPPIST-1 d leading the pack—all four gases can be detected there in fewer than 36 transits. Targets like TOI-700 d and LP 890-9 c would require hundreds of transits, making them practically out of reach for sensible observing programs.
Implications
These results paint a realistic, albeit optimistic, picture of hunting for biosignatures with next-generation ground-based telescopes. They highlight that even under ideal conditions, detecting oxygen remains a monumental challenge requiring years-long campaigns. Meanwhile, lighter molecules like water and carbon dioxide could be spotted within reasonable timeframes, opening the door to statistical studies of climate and potential habitability on planets around red dwarfs.
Future development
Advances in suppressing telluric contamination and stellar activity, along with adaptive optics and coronagraphy (HDC mode), will let us expand the target sample to include nearby non-transiting planets. Moreover, future space missions like the Habitable Worlds Observatory could complement ground-based efforts, offering unprecedented sensitivity in the search for biosignatures.
Impact
This study will influence the planning of ELT observing programs and the development of high-resolution spectroscopy methods and Bayesian analysis of astronomical data. The findings are pivotal for astrobiology and our grasp of life's prevalence in the universe.
Next steps
Detailed modeling is needed to assess how clouds, aerosols, and stellar activity affect molecular detectability, along with validation of telluric-line removal techniques on real data from existing high-resolution spectrographs.
Key open problems
This work directly tackles the fundamental challenge of searching for extraterrestrial life and interpreting biosignatures, including the issue of false positives (e.g., abiotic oxygen or methane). It also delves into the atmospheric evolution of Earth-like planets under the intense activity of red dwarfs.
The knowledge machine's view
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This study presents numerical simulations of transmission spectra for 18 rocky exoplanets from the Habitable Worlds Catalog to assess the detectability of biosignatures (H2O, CO2, CH4, O2) with the future ANDES spectrograph on the ELT. High-resolution synthetic spectra were generated using the petitRADTRANS code with realistic noise, and detection significance was determined via Bayesian analysis of the cross-correlation function. Water vapor proves to be the most accessible, and for several planets, such as TRAPPIST-1 d, all four gases could be detected in fewer than 36 transits.
Where its strength is
The strength of this work lies in its quantitative assessment of the number of transits required for confident detection of key molecules on specific planets, providing a practical benchmark for planning observational programs with ELT/ANDES. Particularly valuable is the inclusion of realistic instrument noise characteristics and the statistical rigor of the Bayesian approach.
Where it could go next
- It would be interesting to see how the presence of clouds or aerosols—which in real atmospheres can mask molecular lines—affects these estimates. In our archive, there is a related study discussing how abiotic chemistry can mimic biosignatures, and those insights could be adapted to model false-positive scenarios in cloudy atmospheres.based on: How Not to Mistake Life for Lifeless Chemistry arXiv:2605.15337
- A promising extension would be to examine how a photosynthetic biosphere might alter expected biogas concentrations and shift the required number of transits. A nearby review explores the impact of photosynthesis on the spectra of habitable worlds and could be used to broaden your grid of atmospheric models.based on: Cosmic Artist: How Photosynthesis Paints Habitable Worlds arXiv:2607.03106
Worth trying
- Test incorporating a simple cloud-layer parameterization into the atmospheric model and estimate how much the required number of transits for detecting water and CO2 would increase.
- Investigate how the detectability difference between biogenic and abiogenic oxygen changes when adding accompanying gases (e.g., CO), following the discussion of false biosignatures in a related study.
- Compare the obtained detection thresholds with predictions for planets with hypothetical hydrogen-dominated atmospheres, using models from a companion analysis on volcanic H2 sources.
Why this may matter
Such estimates are critical for allocating observing time on the ELT—the most expensive astronomical facility of the coming decades. Knowing how many nights are needed for the first detection of water or oxygen on a given planet directly shapes the strategy for the search for life beyond the Solar System.
Nearby works in our archive
- A Planet’s Breathing Unveils the Mystery of Lifesimilarity 0.67
- The Colors of Life on Distant Planetssimilarity 0.67
- A Sun-Sized Lens Searches for Life Around Distant Starssimilarity 0.67
- How Not to Mistake Life for Lifeless Chemistrysimilarity 0.65
- Cosmic Artist: How Photosynthesis Paints Habitable Worldssimilarity 0.65
- Hunting Ancient Civilizations Through Cosmic Dustsimilarity 0.63
The closest work in the archive sits at 0.67 by meaning — the usual level for our corpus.
The TRAPPIST-1 system lies just 12 parsecs away; if you plopped it into the heart of our Solar System, all seven planets would fit inside Mercury's orbit, yet thanks to the star's low luminosity, three of them receive roughly the same warmth as Earth.
Key numbers
- minimum transits for H2O (TRAPPIST-1 d): 10
- ANDES resolving power: 100 000
- ELT diameter: 39 m
- number of planets in sample: 18
- transit ratio O2/H2O: ~4