From Solar System to Exoplanets: What can we learn from Planetary Spectroscopy?

Encrenaz, Thérèse

doi:10.1088/1674-4527/ac97d1

Cited by 2 publications

(2 citation statements)

References 50 publications

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“…Our strong detection of CH 4 at 5σ resolves one of the longest-standing conundrums in exoplanet science -"The Missing Methane Problem" (Stevenson et al 2010;Madhusudhan & Seager 2011). Low-temperature molecules such as CH 4 and NH 3 are common in the solar system and are seen in the atmospheres of the giant planets (Karkoschka 1998;Encrenaz 2022;Atreya et al 2018). These molecules are expected to be prominent carriers of carbon and nitrogen in H 2 -rich atmospheres at temperatures below ∼600 K, with H 2 O being the dominant oxygen carrier (Burrows & Sharp 1999;Lodders & Fegley 2002).…”

Section: Resolving the Missing Methane Problemmentioning

confidence: 62%

Habitability and Biosignatures of Hycean Worlds

Madhusudhan

Piette

Constantinou

2021

ApJ

124

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The search for habitable environments and biomarkers in exoplanetary atmospheres is the holy grail of exoplanet science. The detection of atmospheric signatures of habitable Earth-like exoplanets is challenging owing to their small planet-star size contrast and thin atmospheres with high mean molecular weight. Recently, a new class of habitable exoplanets, called Hycean worlds, has been proposed, defined as temperate ocean-covered worlds with H 2 -rich atmospheres. Their large sizes and extended atmospheres, compared to rocky planets of the same mass, make Hycean worlds significantly more accessible to atmospheric spectroscopy with JWST. Here we report a transmission spectrum of the candidate Hycean world K2-18 b, observed with the JWST NIRISS and NIRSpec instruments in the 0.9-5.2 µm range. The spectrum reveals strong detections of methane (CH 4 ) and carbon dioxide (CO 2 ) at 5σ and 3σ confidence, respectively, with high volume mixing ratios of ∼1% each in a H 2rich atmosphere. The abundant CH 4 and CO 2 along with the nondetection of ammonia (NH 3 ) are consistent with chemical predictions for an ocean under a temperate H 2 -rich atmosphere on K2-18 b. The spectrum also suggests potential signs of dimethyl sulfide (DMS), which has been predicted to be an observable biomarker in Hycean worlds, motivating considerations of possible biological activity on the planet. The detection of CH 4 resolves the long-standing missing methane problem for temperate exoplanets and the degeneracy in the atmospheric composition of K2-18 b from previous observations. We discuss possible implications of the findings, open questions, and future observations to explore this new regime in the search for life elsewhere.

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Section: Resolving the Missing Methane Problemmentioning

confidence: 62%

Habitability and Biosignatures of Hycean Worlds

Madhusudhan

Piette

Constantinou

2021

ApJ

124

View full text Add to dashboard Cite

show abstract

“…Our strong detection of CH 4 at 5σ resolves one of the longeststanding conundrums in exoplanet science-"The Missing Methane Problem" (Stevenson et al 2010;Madhusudhan & Seager 2011). Low-temperature molecules such as CH 4 and NH 3 are common in the solar system and are seen in the atmospheres of the giant planets (Karkoschka 1998;Encrenaz 2022;Atreya et al 2018). These molecules are expected to be prominent carriers of carbon and nitrogen in H 2 -rich atmospheres at temperatures below ∼600 K, with H 2 O being the dominant oxygen carrier (Burrows & Sharp 1999;Lodders & Fegley 2002).…”

Section: Resolving the Missing Methane Problemmentioning

confidence: 99%

Carbon-bearing Molecules in a Possible Hycean Atmosphere

Madhusudhan,

Sarkar,

Constantinou

et al. 2023

ApJL

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The search for habitable environments and biomarkers in exoplanetary atmospheres is the holy grail of exoplanet science. The detection of atmospheric signatures of habitable Earth-like exoplanets is challenging owing to their small planet–star size contrast and thin atmospheres with high mean molecular weight. Recently, a new class of habitable exoplanets, called Hycean worlds, has been proposed, defined as temperate ocean-covered worlds with H2-rich atmospheres. Their large sizes and extended atmospheres, compared to rocky planets of the same mass, make Hycean worlds significantly more accessible to atmospheric spectroscopy with JWST. Here we report a transmission spectrum of the candidate Hycean world K2-18 b, observed with the JWST NIRISS and NIRSpec instruments in the 0.9–5.2 μm range. The spectrum reveals strong detections of methane (CH4) and carbon dioxide (CO2) at 5σ and 3σ confidence, respectively, with high volume mixing ratios of ∼1% each in a H2-rich atmosphere. The abundant CH4 and CO2, along with the nondetection of ammonia (NH3), are consistent with chemical predictions for an ocean under a temperate H2-rich atmosphere on K2-18 b. The spectrum also suggests potential signs of dimethyl sulfide (DMS), which has been predicted to be an observable biomarker in Hycean worlds, motivating considerations of possible biological activity on the planet. The detection of CH4 resolves the long-standing missing methane problem for temperate exoplanets and the degeneracy in the atmospheric composition of K2-18 b from previous observations. We discuss possible implications of the findings, open questions, and future observations to explore this new regime in the search for life elsewhere.

show abstract

From Solar System to Exoplanets: What can we learn from Planetary Spectroscopy?

Cited by 2 publications

References 50 publications

Habitability and Biosignatures of Hycean Worlds

Habitability and Biosignatures of Hycean Worlds

Carbon-bearing Molecules in a Possible Hycean Atmosphere

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