Detection of Aerosols at Microbar Pressures in an Exoplanet Atmosphere

Estrela, Raissa; Swain, Mark R.; Roudier, G.; West, Robert A.; Sedaghati, E.; Válio, Adriana

doi:10.3847/1538-3881/ac0c7c

Cited by 13 publications

(22 citation statements)

References 73 publications

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“…Its low gravitational potential makes it an excellent target for atmospheric observations. To date, observations of this planet's lower atmosphere have revealed water absorption, sodium absorption, and a Rayleigh scattering slope indicating the presence of hazes (Tsiaras et al 2018;Murgas et al 2020;Estrela et al 2021;Khalafinejad et al 2021). Additionally, Nortmann et al (2018) detected helium escaping from the upper atmosphere of WASP-69b with two nights of CAR-MENES observations.…”

Section: Wasp-69bmentioning

confidence: 99%

The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation

Vissapragada¹,

Knutson²,

Greklek-McKeon³

et al. 2022

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Transit surveys indicate that there is a deficit of Neptune-sized planets on close-in orbits. If this “Neptune desert” is entirely cleared out by atmospheric mass loss, then planets at its upper edge should only be marginally stable against photoevaporation, exhibiting strong outflow signatures in tracers like the metastable helium triplet. We test this hypothesis by carrying out a 12-night photometric survey of the metastable helium feature with Palomar/WIRC, targeting seven gas-giant planets orbiting K-type host stars. Eight nights of data are analyzed here for the first time along with reanalyses of four previously published data sets. We strongly detect helium absorption signals for WASP-69b, HAT-P-18b, and HAT-P-26b; tentatively detect signals for WASP-52b and NGTS-5b; and do not detect signals for WASP-177b and WASP-80b. We interpret these measured excess absorption signals using grids of Parker wind models to derive mass-loss rates, which are in good agreement with predictions from the hydrodynamical outflow code ATES for all planets except WASP-52b and WASP-80b, where our data suggest that the outflows are much smaller than predicted. Excluding these two planets, the outflows for the rest of the sample are consistent with a mean energy-limited outflow efficiency of ε = 0.41 − 0.13 + 0.16 . Even when we make the relatively conservative assumption that gas-giant planets experience energy-limited outflows at this efficiency for their entire lives, photoevaporation would still be too inefficient to carve the upper boundary of the Neptune desert. We conclude that this feature of the exoplanet population is a pristine tracer of giant planet formation and migration mechanisms.

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Section: Wasp-69bmentioning

confidence: 99%

The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation

Vissapragada¹,

Knutson²,

Greklek-McKeon³

et al. 2022

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“…atmosphere have revealed water absorption, sodium absorption, and a Rayleigh scattering slope indicating the presence of hazes (Tsiaras et al 2018;Murgas et al 2020;Estrela et al 2021;Khalafinejad et al 2021). Additionally, Nortmann et al ( 2018) detected helium escaping from the upper atmosphere of WASP-69b with two nights of CARMENES observations.…”

Section: Wasp-69bmentioning

confidence: 99%

The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation

Vissapragada¹,

Knutson²,

Greklek-McKeon³

et al. 2022

Preprint

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Transit surveys indicate that there is a deficit of Neptune-sized planets on close-in orbits. If this "Neptune desert" is entirely cleared out by atmospheric mass loss, then planets at its upper edge should only be marginally stable against photoevaporation, exhibiting strong outflow signatures in tracers like the metastable helium triplet. We test this hypothesis by carrying out a 12-night photometric survey of the metastable helium feature with Palomar/WIRC, targeting seven gas-giant planets orbiting K-type host stars. Eight nights of data are analyzed here for the first time along with reanalyses of four previously-published datasets. We strongly detect helium absorption signals for WASP-69b, HAT-P-18b, and HAT-P-26b; tentatively detect signals for WASP-52b and NGTS-5b; and do not detect signals for WASP-177b and WASP-80b. We interpret these measured excess absorption signals using grids of isothermal Parker wind models to derive mass-loss rates, which are typically around 10 10 − 10 11 g s −1 . Our empirically constrained mass-loss rates are in good agreement with predictions from the 1D hydrodynamical outflow code ATES for all planets except WASP-52b and WASP-80b, where our data suggest that the outflows are much smaller than predicted. Excluding these two planets, the outflows for the rest of the sample are consistent with a mean energy-limited outflow efficiency of ε = 0.41 +0.16 −0.13 . Even when we make the relatively conservative assumption that gas-giant planets experience energy-limited outflows at this efficiency for their entire lives, photoevaporation would still be too inefficient to carve the upper boundary of the Neptune desert. We conclude that this feature of the exoplanet population is a pristine tracer of giant planet formation and migration mechanisms.

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“…A uniformly processed catalog is particularly important when performing comparative planetology because differences in planetary spectra can be attributed to differences in astrophysics rather than analysis methods. Second, this catalog is based on the EXoplanet CALIbration and Bayesian Unified Retrieval (EXCALIBUR) pipeline (Swain et al 2021;Roudier et al 2021;Estrela et al 2021;Huber-Feely et al 2022), which processes HST/WFC3-G141 data at the full spectral resolution of the instrument. Using the full G141 spectral resolution avoids the potential reduction in spectral feature amplitude that can be caused by additional spectral averaging.…”

Section: Methodsmentioning

confidence: 99%

“…The cloudy and hazy atmospheres are associated with a weaker absorption feature in the NIR portion of the transmission spectrum of the planet or a featureless spectra (Knutson et al 2014a,b;Kreidberg et al 2014). While in the optical spectra, they can cause Rayleigh scattering-like opacity seen in several planets (Pont et al 2008(Pont et al , 2013McCullough et al 2014;Sing et al 2016;Estrela et al 2021). These clouds are generally attributed to atmospheric condensates of salt, silicate, and metal vapors (Morley et al 2012;Zhang 2020;Gao et al 2020), or to photochemically produced hazes due to energy input or energetic particle bombardment (Lavvas & Koskinen 2017;Lavvas et al 2019;Gao et al 2020;Lavvas & Arfaux 2021).…”

Section: Introductionmentioning

confidence: 99%

“…Many species, such as TiO/VO and metals, have been suggested to be present in ultrahot Jupiters (Ben-Yami et al 2020;Cabot et al 2020), while smaller and cooler planets (sub-Neptunes and super-Earths) also have indicated the presence of high-altitude aerosols in their atmospheres (Ehrenreich et al 2014;Wakeford et al 2017;Kreidberg et al 2020). Other planets have shown very steep optical slope in their spectra (Alderson et al 2020;Estrela et al 2021;Chen et al 2021) due to scattering in the atmosphere, which could be explained by sulphide clouds (MnS, ZnS, Na 2 S) (Pinhas & Madhusudhan 2017). High-altitude photochemical hazes could also lead to super-Rayleigh optical slope, depending on their mixing and formation rate (Ohno & Kawashima 2020).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Temperature Trend for Clouds and Hazes in Exoplanets Atmospheres

Estrela¹,

Swain²,

Roudier³

2022

Preprint

Self Cite

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The transmission spectra of exoplanet atmospheres observed with the Hubble Space Telescope in the near-infrared range (1.1-1.65µm) frequently show evidence for some combination of clouds and hazes. Identification of systematic trends in exoplanet clouds and hazes is potentially important for understanding atmospheric composition and temperature structure. Here we report on the analysis of spectral modulation using the largest uniformly processed sample of exoplanet transit spectra currently available. The spectral retrieval includes the capability to detect and represent atmospheres in which the composition departs from thermochemical equilibrium. Using this catalog, we find that the impact of clouds/hazes, measured in terms of damping of spectral features, follows a trend from mostly cloudy/hazy around 500 K to mostly clear around 1650 K. For planets at lower temperatures (< 270 K), we observe a potential rise towards reduced cloudy/hazy atmospheres. We also find that a partially transparent aerosol component is frequently present and that it is typically vertically distributed throughout the atmospheric column. Our findings also suggest that while clouds and hazes are common in exoplanet atmospheres, the majority of planets have detectable spectral modulation that is sufficient for characterizing their atmospheres. Additionally, the empirical trend that clouds and hazes are minimized at 1650 +874 −620 K revealed in our catalog has predictive utility for modelling the performance of large-scale transiting exoplanets survey, such as planned with the Ariel mission. This trend can also be used for making a probability-based forecast of spectral modulation for a given source in the context of future JWST observations.

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Detection of Aerosols at Microbar Pressures in an Exoplanet Atmosphere

Cited by 13 publications

References 73 publications

The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation

The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation

The Upper Edge of the Neptune Desert Is Stable Against Photoevaporation

A Temperature Trend for Clouds and Hazes in Exoplanets Atmospheres

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