No Detectable H3+ Emission from the Atmospheres of Hot Jupiters

Abstract

H${}_3^{+}$ emission is the dominant cooling mechanism in Jupiter's thermosphere and a useful probe of temperature and ion densities. The H${}_3^{+}$ ion is predicted to form in the thermospheres of close-in `hot Jupiters' where its emission would be a significant factor in the thermal energy budget, affecting temperature and the rate of hydrogen escape from the exosphere. Hot Jupiters are predicted to have up to 10${}^5$ times Jupiter's H${}_3^{+}$ emission because they experience extreme stellar irradiation and enhanced interactions may occur between the planetary magnetosphere and the stellar wind. Direct (but unresolved) detection of an extrasolar planet, or the establishment of useful upper limits, may be possible because a small but significant fraction of the total energy received by the planet is re-radiated in a few narrow lines of H${}_3^{+}$ within which the flux from the star is limited. We present the observing strategy and results of our search for emission from the Q(1,0) transition of H${}_3^{+}$ (3.953~$\mu$m) from extrasolar planets orbiting six late-type dwarfs using CSHELL, the high-resolution echelle spectrograph on NASA's Infrared Telescope Facility (IRTF). We exploited the time-dependent Doppler shift of the planet, which can be as large as 150 km s${}^{-1}$, by differencing spectra between nights, thereby removing the stellar photospheric signal and telluric lines. We set limits on the H${}_3^{+}$ emission from each of these systems and compare them with models in the literature. Ideal candidates for future searches are intrinsically faint stars, such as M dwarfs, at very close distances.

arXiv commentAccepted to the Astronomical Journal. Contains 20 pages including 6 figures

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Cited by in corpus (10)

• Characterizing the thermosphere of HD209458b with UV transit observations
• ExoMol molecular line lists XX: a comprehensive line list for H${}_3^{+}$
• EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars
• The Sun and stars as the primary energy input in planetary atmospheres
• Ions in the Thermosphere of Exoplanets: Observable Constraints Revealed by Innovative Laboratory Experiments
• Lightning and charge processes in brown dwarf and exoplanet atmospheres
• Limits on the Auroral Generation of H${}_3^{+}$ in Brown Dwarf and Extrasolar Giant Planet Atmospheres with Keck/NIRSPEC
• The Upper Atmosphere of HD17156b
• The Occurrence Rate of Quiescent Radio Emission for Ultracool Dwarfs using a Generalized Semi-Analytical Bayesian Framework
• A CRIRES-search for H3+ emission from the hot Jupiter atmosphere of HD 209458 b