The First Near-Infrared Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System

Abstract

We present a near-infrared transmission spectrum of the long period (P=542 days), temperate ($T_{eq}$=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope (HST). With a measured mass of 12 $\pm$ 3 $M_{\oplus }$ and a radius of 9.2 $\pm$ 0.1 $R_{\oplus }$, HIP 41378 f has an extremely low bulk density (0.09 $\pm$ 0.02 g/cm${}^3$). We measure the transit depth with a median precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.

12 pages, 4 figures, accepted to ApJL. Please also see companion paper Ohno & Fortney (2022) for further details on the ring modeling methodology (arxiv DOI: 2201.02794)

References in corpus (21)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• The Stagger-grid: A grid of 3D stellar atmosphere models - IV. Limb darkening coefficients
• Trends in Atmospheric Properties of Neptune-Size Exoplanets
• The Featureless Transmission Spectra of Two Super-Puff Planets
• Deflating Super-Puffs: Impact of Photochemical Hazes on the Observed Mass-Radius Relationship of Low Mass Planets
• Tidally-Induced Radius Inflation of Sub-Neptunes
• Hubble WFC3 Spectroscopy of the Habitable-zone Super-Earth LHS 1140 b
• Sulfur Hazes in Giant Exoplanet Atmospheres: Impacts on Reflected Light Spectra
• Dusty outflows in planetary atmospheres: Understanding "super-puffs" and transmission spectra of sub-Neptunes
• Five Planets Transiting a Ninth Magnitude Star
• Aggregate Hazes in Exoplanet Atmospheres
• Haze Evolution in Temperate Exoplanet Atmospheres Through Surface Energy Measurements
• LRG-BEASTS III: Ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80
• Compositions and origins of outer planet systems: Insights from the Roche critical density
• The HST PanCET Program: An Optical to Infrared Transmission Spectrum of HAT-P-32Ab
• Ohmic Dissipation in Mini-Neptunes
• Evidence of a Clear Atmosphere for WASP-62b: the Only Known Transiting Gas Giant in the JWST Continuous Viewing Zone
• An extremely low-density and temperate giant exoplanet
• The rings of Neptune
• Why are dense planetary rings only found between 8 and 20 AU?
• Uranus' hidden narrow rings

Cited by in corpus (7)

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• LRG-BEASTS: Evidence for clouds in the transmission spectrum of HATS-46 b
• Tighter constraints on the atmosphere of GJ 436 b from combined high-resolution CARMENES and CRIRES${}^{+}$ observations
• Search for Exoplanetary Ring Systems with TESS
• The Hubble PanCET Program: A Featureless Transmission Spectrum for WASP-29b and Evidence of Enhanced Atmospheric Metallicity on WASP-80b
• A Multi-Planet System's Sole Super-Puff: Exploring Allowable Physical Parameters for the Cold Super-Puff HIP 41378 f