Hubble WFC3 Spectroscopy of the Terrestrial Planets L 98–59 c and d: No Evidence for a Clear Hydrogen Dominated Primary Atmosphere

Zhou, Li; Ma, Bo; Wang, Yonghao; Zhu, Yinan

doi:10.1088/1674-4527/acaceb

Cited by 12 publications

(4 citation statements)

References 69 publications

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“…With the data presented in this work we rule out a clear, lowmean-molecular-weight atmosphere at 10 bars of surface pressure (3.2σ) and 1 bar of surface pressure (3.1σ). This result joins previous work on GJ 1132b (Diamond-Lowe et al 2018;Mugnai et al 2021;Libby-Roberts et al 2022), TRAPPIST-1a-f (de Wit et al 2016), LHS 3844 (Diamond-Lowe et al 2020b), L 98-59b-d (Damiano et al 2022Zhou et al 2022Zhou et al , 2023Barclay et al 2023), andLHS 475b (Lustig-Yaeger et al 2023) to strongly suggest that highly-irradiated terrestrial exoplanets orbiting M dwarfs are not capable of retaining low-mean-molecular-weight atmospheres, if they are able to accrete them in the first place. It is possible, however, that LTT 1445Ab possesses a high-meanmolecular-weight or cloudy/hazy atmosphere, which would fall below our detection limits, or no atmosphere at all.…”

Section: Discussionsupporting

confidence: 90%

Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab

Diamond-Lowe

Mendonça

Charbonneau

et al. 2023

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Nearby M-dwarf systems currently offer the most favorable opportunities for spectroscopic investigations of terrestrial exoplanet atmospheres. The LTT 1445 system is a hierarchical triple of M dwarfs with two known planets orbiting the primary star, LTT 1445A. We observe four transits of the terrestrial world LTT 1445Ab (R = 1.3 R ⊕, M = 2.9 M ⊕) at low resolution with Magellan II/LDSS3C. We use the combined flux of the LTT 1445BC pair as a comparison star, marking the first time that an M dwarf is used to remove telluric variability from time-series observations of another M dwarf. We find Hα in emission from both LTT 1445B and C, as well as a flare in one of the data sets from LTT 1445C. These contaminated data are removed from the analysis. We construct a broadband transit light curve of LTT 1445Ab from 620 to 1020 nm. Binned to 3 minute time bins, we achieve an rms of 49 ppm for the combined broadband light curve. We construct a transmission spectrum with 20 spectrophotometric bins each spanning 20 nm and compare it to models of clear, 1× solar composition atmospheres. We rule out this atmospheric case with a surface pressure of 10 bars to 3.2σ confidence, and with a surface pressure of 1 bar to 3.1σ confidence. Upcoming secondary eclipse observations of LTT 1445Ab with the James Webb Space Telescope will further probe the cases of a high-mean-molecular-weight atmosphere, a hazy or cloudy atmosphere, or no atmosphere at all on this terrestrial world.

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Section: Discussionsupporting

confidence: 90%

Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab

Diamond-Lowe

Mendonça

Charbonneau

et al. 2023

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“…Such planets include the first planet of our JWST-GO-1981 program, LHS 475b, existing observations of which cannot distinguish a carbon dioxide atmosphere from an airless body (Lustig-Yaeger et al 2023). L 98-59c is another planet where recent Hubble Space Telescope observations have tentatively suggested either a hydrogen-rich planetary atmosphere or stellar contamination (Barclay et al 2023)-though a different analysis favored a flat, featureless transmission spectrum (Zhou et al 2023). Both GJ 486b at 1.3 R ⊕ and L 98-59c at 1.35 R ⊕ track the upper edge of planets below the expected hydrogen-dominated atmospheric cutoff (Rogers 2015;Rogers et al 2021).…”

Section: Discussionmentioning

confidence: 97%

“…Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Gressier et al 2022), GJ 1132b(Diamond-Lowe et al 2018Mugnai et al 2021;Libby-Roberts et al 2022), the L 98-59 system (Damiano et al 2022;Zhou et al 2023), LTT 1445Ab (Diamond-Lowe et al 2022, and LHS 3488b (Kreidberg et al 2019;Diamond-Lowe et al 2020). However, many of these observations do not preclude higher mean molecular weight secondary atmospheres for these small planets (Moran et al 2018;Damiano et al 2022).…”

Section: Introductionmentioning

confidence: 98%

High Tide or Riptide on the Cosmic Shoreline? A Water-rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations

Moran

Stevenson

Sing

et al. 2023

ApJL

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Planets orbiting M-dwarf stars are prime targets in the search for rocky exoplanet atmospheres. The small size of M dwarfs renders their planets exceptional targets for transmission spectroscopy, facilitating atmospheric characterization. However, it remains unknown whether their host stars’ highly variable extreme-UV radiation environments allow atmospheres to persist. With JWST, we have begun to determine whether or not the most favorable rocky worlds orbiting M dwarfs have detectable atmospheres. Here, we present a 2.8–5.2 μm JWST NIRSpec/G395H transmission spectrum of the warm (700 K, 40.3× Earth’s insolation) super-Earth GJ 486b (1.3 R ⊕ and 3.0 M ⊕). The measured spectrum from our two transits of GJ 486b deviates from a flat line at 2.2σ − 3.3σ, based on three independent reductions. Through a combination of forward and retrieval models, we determine that GJ 486b either has a water-rich atmosphere (with the most stringent constraint on the retrieved water abundance of H2O > 10% to 2σ) or the transmission spectrum is contaminated by water present in cool unocculted starspots. We also find that the measured stellar spectrum is best fit by a stellar model with cool starspots and hot faculae. While both retrieval scenarios provide equal quality fits ( χ ν 2 = 1.0 ) to our NIRSpec/G395H observations, shorter wavelength observations can break this degeneracy and reveal if GJ 486b sustains a water-rich atmosphere.

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“…Measurements obtained with the Hubble Space Telescope (HST) of L 98-59 b were consistent with no atmosphere (Damiano et al 2022;Zhou et al 2022). However, Barclay et al (2023) presented preliminary and marginal evidence of an atmosphere on L 98-59 c with HST measurements, although this has since been debated (Zhou et al 2023).…”

Section: Exoplanets With Properties Amenable To Volcanismmentioning

confidence: 99%

Potential Melting of Extrasolar Planets by Tidal Dissipation

Seligman,

Feinstein,

Lai

et al. 2024

ApJ

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Tidal heating on Io due to its finite eccentricity was predicted to drive surface volcanic activity, which was subsequently confirmed by the Voyager spacecraft. Although the volcanic activity in Io is more complex, in theory volcanism can be driven by runaway melting in which the tidal heating increases as the mantle thickness decreases. We show that this runaway melting mechanism is generic for a composite planetary body with liquid core and solid mantle, provided that (i) the mantle rigidity, μ, is comparable to the central pressure, i.e., μ/(ρ gR P) ≳ 0.1 for a body with density ρ, surface gravitational acceleration g, and radius R P; (ii) the surface is not molten; (iii) tides deposit sufficient energy; and (iv) the planet has nonzero eccentricity. We calculate the approximate liquid core radius as a function of μ/(ρ gR P), and find that more than 90% of the core will melt due to this runaway for μ/(ρ gR P) ≳ 1. From all currently confirmed exoplanets, we find that the terrestrial planets in the L 98-59 system are the most promising candidates for sustaining active volcanism. However, uncertainties regarding the quality factors and the details of tidal heating and cooling mechanisms prohibit definitive claims of volcanism on any of these planets. We generate synthetic transmission spectra of these planets assuming Venus-like atmospheric compositions with an additional 5%, 50%, and 98% SO2 component, which is a tracer of volcanic activity. We find a ≳3σ preference for a model with SO2 with 5–10 transits with JWST for L 98-59bcd.

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Hubble WFC3 Spectroscopy of the Terrestrial Planets L 98–59 c and d: No Evidence for a Clear Hydrogen Dominated Primary Atmosphere

Cited by 12 publications

References 69 publications

Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab

Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab

High Tide or Riptide on the Cosmic Shoreline? A Water-rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations

Potential Melting of Extrasolar Planets by Tidal Dissipation

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