Shallow-water Magnetohydrodynamics for Westward Hotspots on Hot Jupiters

Hindle, A. W.; Bushby, P. J.; Rogers, T. M.

doi:10.3847/2041-8213/ab05dd

Cited by 39 publications

(54 citation statements)

References 29 publications

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“…The large offset could be due to MHD effects that are not currently accounted for in the GCM used in this work. Future work investigating how magnetic effects influence both the hot spot offset and the phase curve amplitude (e.g., Rogers & Komacek 2014;Rogers 2017;Hindle et al 2019) could shed light on the remaining discrepancies between the Spitzer observations and GCMs. Table 1 and Equation 1.…”

Section: Discussionmentioning

confidence: 99%

Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Mansfield

Bean

Stevenson

et al. 2020

ApJL

121

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Phase curve observations provide an opportunity to study the full energy budgets of exoplanets by quantifying the amount of heat redistributed from their daysides to their nightsides. Theories explaining the properties of phase curves for hot Jupiters have focused on the balance between radiation and dynamics as the primary parameter controlling heat redistribution. However, recent phase curves have shown deviations from the trends that emerge from this theory, which has led to work on additional processes that may affect hot Jupiter energy budgets. One such process, molecular hydrogen dissociation and recombination, can enhance energy redistribution on ultra-hot Jupiters with temperatures above ∼ 2000 K. In order to study the impact of H 2 dissociation on ultra-hot Jupiters, we present a phase curve of KELT-9b observed with the Spitzer Space Telescope at 4.5 µm. KELT-9b is the hottest known transiting planet, with a 4.5-µm dayside brightness temperature of 4566 +140 −136 K and a nightside temperature of 2556 +101 −97 K. We observe a phase curve amplitude of 0.609 ± 0.020 and a hot spot offset of 18.7 +2.1 −2.3 • . The observed amplitude is too small to be explained by a simple balance between radiation and advection. General circulation models (GCMs) and an energy balance model that include the effects of H 2 dissociation and recombination provide a better match to the data. The GCMs, however, predict a maximum hot spot offset of 5 • , which disagrees with our observations at > 5σ confidence. This discrepancy may be due to magnetic effects in the planet's highly ionized atmosphere.

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Section: Discussionmentioning

confidence: 99%

Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Mansfield

Bean

Stevenson

et al. 2020

ApJL

121

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“…Magnetic drag can also reduce eastward phase offsets, or produce westward offsets (Rauscher, & Menou 2013;Hindle et al 2019). At high enough equilibrium temperatures, alkali metals in a planet's atmosphere thermally ionize and interact with the planet's magnetic field, acting as a source of drag.…”

Section: Phase Offsetsmentioning

confidence: 99%

Smaller than Expected Bright-spot Offsets in Spitzer Phase Curves of the Hot Jupiter Qatar-1b

Keating

Stevenson

Cowan

et al. 2020

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We present Spitzer full-orbit thermal phase curves of the hot Jupiter Qatar-1b, a planet with the same equilibrium temperature-and intermediate surface gravity and orbital period-as the well-studied planets HD 209458b and WASP-43b. We measure secondary eclipse of 0.21 ± 0.02% at 3.6 µm and 0.30±0.02% at 4.5 µm, corresponding to dayside brightness temperatures of 1542 +32 −31 K and 1557 +35 −36 K, respectively, consistent with a vertically isothermal dayside. The respective nightside brightness temperatures are 1117 +76 −71 K and 1167 +69 −74 K, in line with a trend that hot Jupiters all have similar nightside temperatures. We infer a Bond albedo of 0.12 +0.14 −0.16 and a moderate day-night heat recirculation efficiency, similar to HD 209458b. General circulation models for HD 209458b and WASP-43b predict that their bright-spots should be shifted east of the substellar point by tens of degrees, and these predictions were previously confirmed with Spitzer full-orbit phase curve observations. The phase curves of Qatar-1b are likewise expected to exhibit eastward offsets. Instead, the observed phase curves are consistent with no offset: 11 • ± 7 • at 3.6 µm and −4 • ± 7 • at 4.5 µm. The discrepancy in circulation patterns between these three otherwise similar planets points to the importance of secondary parameters like rotation rate and surface gravity, and the presence or absence of clouds, in determining atmospheric conditions on hot Jupiters.

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“…The time variable offset of HAT-P-7b may be explained by an oscillation of the equatorial wind triggered by magneto-hydrodynamical effects (Rogers 2017). However, magnetic interactions are unlikely to explain the case of CoRoT-2b (Hindle et al 2019), whose brightness offset may originate from asynchronous rotation (Rauscher & Kempton 2014). The question remains how the observed circulation patterns extend from the classical hot Jupiters to the population of UHJs, for which the additional chemistry and physics that has been identified influences their circulation.…”

Section: Introductionmentioning

confidence: 99%

Climate of an ultra hot Jupiter

Arcangeli

Désert

Parmentier

et al. 2019

A&A

105

108

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We present the analysis of a full-orbit, spectroscopic phase curve of the ultra hot Jupiter (UHJ) WASP-18b, obtained with the Wide Field Camera 3 aboard the Hubble Space Telescope. We measured the normalised day-night contrast of the planet as >0.96 in luminosity: the disc-integrated dayside emission from the planet is at 964 ± 25 ppm, corresponding to 2894 ± 30 K, and we place an upper limit on the nightside emission of <32 ppm or 1430 K at the 3σ level. We also find that the peak of the phase curve exhibits a small, but significant offset in brightness of 4.5 ± 0.5° eastward. We compare the extracted phase curve and phase-resolved spectra to 3D global circulation models and find that broadly the data can be well reproduced by some of these models. We find from this comparison several constraints on the atmospheric properties of the planet. Firstly we find that we need efficient drag to explain the very inefficient day-night recirculation observed. We demonstrate that this drag could be due to Lorentz-force drag by a magnetic field as weak as 10 gauss. Secondly, we show that a high metallicity is not required to match the large day-night temperature contrast. In fact, the effect of metallicity on the phase curve is different from cooler gas-giant counterparts because of the high-temperature chemistry in the atmosphere of WASP-18b. Additionally, we compared the current UHJ spectroscopic phase curves, WASP-18b and WASP-103b, and show that these two planets provide a consistent picture with remarkable similarities in their measured and inferred properties. However, key differences in these properties, such as their brightness offsets and radius anomalies, suggest that UHJ could be used to separate between competing theories for the inflation of gas-giant planets.

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Shallow-water Magnetohydrodynamics for Westward Hotspots on Hot Jupiters

Cited by 39 publications

References 29 publications

Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Smaller than Expected Bright-spot Offsets in Spitzer Phase Curves of the Hot Jupiter Qatar-1b

Climate of an ultra hot Jupiter

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