Confirmation of Subsolar Metallicity for WASP-77Ab from JWST Thermal Emission Spectroscopy

August, Prune C.; Bean, Jacob L.; Zhang, Michael; Lunine, Jonathan; Xue, Qiao; Line, Michael; Smith, Peter C. B.

doi:10.3847/2041-8213/ace828

Cited by 31 publications

(28 citation statements)

References 56 publications

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“…The last case is the most conservative and is motivated by the transit depth offset between NRS1 and NRS2 recently reported by Moran et al (2023). The offset on either NIRISS or NIRSpec represents cases where we assume no offset between NIRSpec NRS1 and NRS2 (Alderson et al 2023;August et al 2023;Lustig-Yaeger et al 2023) but instead allow for an offset between NIRISS and NIRSpec as a whole. In the no-offset case, we consider the data as is and do not perform any offsets.…”

Section: Retrieval Setupmentioning

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.

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Section: Retrieval Setupmentioning

confidence: 99%

Carbon-bearing Molecules in a Possible Hycean Atmosphere

Madhusudhan,

Sarkar,

Constantinou

et al. 2023

ApJL

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“…Ultimately, the combined analysis did not qualitatively change the previous interpretations of WASP-77A b's atmosphere by Line et al (2021) and August et al (2023). However, the excellent agreement between IGRINS and NIRspec greatly increases the confidence in the accuracy of these interpretations, as well as those from the combined analysis itself.…”

Section: Comparing the Predictive Power Of Igrins And Nirspecmentioning

confidence: 62%

“…Using a similar free retrieval framework to Line et al (2021), they were unable to obtain any informative composition constraints, only placing a subsolar lower limit on the metallicity broadly consistent with the IGRINS results. Again, WASP-77A b was recently observed in eclipse using NIRSpec/G395H on the James Webb Space Telescope (JWST; August et al 2023). Bounded constraints could be placed on the abundances of H 2 O and CO, and an upper limit was placed on the abundance of CO 2 when applying a free retrieval, showing a clear improvement over WFC3 and allowing the confirmation of the low metallicity measured with IGRINS by Line et al (2021).…”

Section: Introductionmentioning

confidence: 93%

“…We apply the same retrieval framework to the NIRSpec/ G395H secondary eclipse data presented in August et al (2023). For initial exploratory retrievals with lower model spectral resolution and fewer live points, we include all of the gases used in the high-resolution retrievals in addition to CO 2 and SO 2 , prominent absorbers over the 4-5 μm region.…”

Section: Nirspecmentioning

confidence: 99%

“…With the advent of high-resolution retrievals (Brogi & Line 2019;Gibson et al 2020), the abundances of both H 2 O and CO, and indirectly [O/H] and [C/H], have been measured in a handful of hot and ultrahot Jupiters in the past few years (Gandhi et al 2019;Line et al 2021;Pelletier et al 2021;Kasper et al 2023). The launch of JWST has increased our capabilities to do so, and already the sample of such measurements has grown (August et al 2023;Bean et al 2023;Taylor et al 2023). Nonetheless, the current dearth of planets in which these two have been reliably estimated is stark (Figure 10), highlighting the long path ahead for characterizing the transiting giant planet population as a whole.…”

Section: Bulk Composition and Placing Wasp-77a B Into Contextmentioning

confidence: 99%

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A Combined Ground-based and JWST Atmospheric Retrieval Analysis: Both IGRINS and NIRSpec Agree that the Atmosphere of WASP-77A b Is Metal-poor

Smith,

Line,

Bean

et al. 2024

Self Cite

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Ground-based high-resolution and space-based low-resolution spectroscopy are the two main avenues through which transiting exoplanet atmospheres are studied. Both methods provide unique strengths and shortcomings, and combining the two can be a powerful probe into an exoplanet’s atmosphere. Within a joint atmospheric retrieval framework, we combined JWST NIRSpec/G395H secondary eclipse spectra and Gemini South/IGRINS pre- and post-eclipse thermal emission observations of the hot Jupiter WASP-77A b. Our inferences from the IGRINS and NIRSpec data sets are consistent with each other, and combining the two allows us to measure the gas abundances of H2O and CO, as well as the vertical thermal structure, with higher precision than either data set provided individually. We confirm WASP-77A b’s subsolar metallicity ([(C+O)/H] = −0.61 − 0.09 + 0.10 ) and solar C/O ratio (C/O = 0.57 − 0.06 + 0.06 ) . The two types of data are complementary, and our abundance inferences are mostly driven by the IGRINS data, while inference of the thermal structure is driven by the NIRSpec data. Our ability to draw inferences from the post-eclipse IGRINS data is highly sensitive to the number of singular values removed in the detrending process, potentially due to high and variable humidity. We also search for signatures for atmospheric dynamics in the IGRINS data and find that propagated ephemeris error can manifest as either an orbital eccentricity or a strong equatorial jet. Neither are detected when using more up-to-date ephemerides. However, we find moderate evidence of thermal inhomogeneity and measure a cooler nightside that presents itself in the later phases after secondary eclipse.

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Enriching inner discs and giant planets with heavy elements

Bitsch,

Mah

2023

A&A

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Giant exoplanets seem to have on average a much higher heavy-element content than the Solar System giants. Past attempts to explain this heavy-element content include collisions between planets, accretion of volatile rich gas, and accretion of gas enriched in micrometre-sized solids. However, these different theories individually could not explain the heavy-element content of giants and the volatile-to-refractory ratios in the atmospheres of giant planets at the same time. Here we combine the approaches of gas accretion enhanced with vapour and small micrometre-sized dust grains within one model. To this end, we present detailed models of inward-drifting and evaporating pebbles, and describe how these pebbles influence the dust-to-gas ratio and the heavy-element content of the disc. As pebbles drift inwards, the volatile component evaporates and enriches the disc. At the same time, the smaller silicate core of the pebble continues to move inwards. As the silicate pebbles are presumably smaller than the ice grains, they drift more slowly, leading to a pile-up of material inside of the water-ice line, increasing the dust-to-gas ratio in this region. Under the assumption that these small dust grains follow the motion of the gas even through the pressure bumps generated by the gaps between planets, gas accreting giants can accrete large fractions of small solids in addition to the volatile vapour. We find that the effectiveness of the solid enrichment requires a large disc radius to maintain the pebble flux for a long time and a high viscosity that reduces the size and inward drift of the small dust grains. However, this process depends crucially on the debated size difference of the pebbles that are inside and outside of the water-ice line. On the other hand, the volatile component released by the inward-drifting pebbles can lead to a high enrichment with heavy-element vapour, independently of a size difference of pebbles inside and outside the water-ice line. Our model emphasises the importance of the disc’s radius and viscosity to the enrichment of dust and vapour. Consequently, we show how our model could explain the heavy-element content of the majority of giant planets by using combined estimates of dust and vapour enrichment.

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Confirmation of Subsolar Metallicity for WASP-77Ab from JWST Thermal Emission Spectroscopy

Cited by 31 publications

References 56 publications

Carbon-bearing Molecules in a Possible Hycean Atmosphere

Carbon-bearing Molecules in a Possible Hycean Atmosphere

A Combined Ground-based and JWST Atmospheric Retrieval Analysis: Both IGRINS and NIRSpec Agree that the Atmosphere of WASP-77A b Is Metal-poor

Enriching inner discs and giant planets with heavy elements

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