Magnetic Effects in Hot Jupiter Atmospheres

Rogers, T. M.; Komacek, Thaddeus D.

doi:10.1088/0004-637x/794/2/132

Cited by 134 publications

(211 citation statements)

References 52 publications

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“…Further theoretical work could help reduce these uncertainties. Our result that Lorentz forces are potentially unimportant for HD 189733b but may be important for HD 209458b therefore agrees with previous estimates that magnetic drag could become significant at T 1400 K eq  (Menou 2012;Rogers & Komacek 2014). In contrast to magnetic drag, we find that shear instabilities are a plausible mechanism to match the observations of both planets ( Figure 5, bottom panel).…”

Section: Evaluating Drag Mechanisms With Observationssupporting

confidence: 92%

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Atmospheric Circulations of Hot Jupiters as Planetary Heat Engines

Koll

Komacek

2018

ApJ

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Because of their intense incident stellar irradiation and likely tidally locked spin states, hot Jupiters are expected to have wind speeds that approach or exceed the speed of sound. In this work, we develop a theory to explain the magnitude of these winds. We model hot Jupiters as planetary heat engines and show that hot Jupiters are always less efficient than an ideal Carnot engine. Next, we demonstrate that our predicted wind speeds match those from three-dimensional numerical simulations over a broad range of parameters. Finally, we use our theory to evaluate how well different drag mechanisms can match the wind speeds observed with Doppler spectroscopy for HD 189733b and HD 209458b. We find that magnetic drag is potentially too weak to match the observations for HD 189733b, but is compatible with the observations for HD 209458b. In contrast, shear instabilities and/or shocks are compatible with both observations. Furthermore, the two mechanisms predict different wind speed trends for hotter and colder planets than currently observed. As a result, we propose that a wider range of Doppler observations could reveal multiple drag mechanisms at play across different hot Jupiters.

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Section: Evaluating Drag Mechanisms With Observationssupporting

confidence: 92%

“…Note that Equation (14) does not include induced atmospheric fields. In strongly ionized atmospheres, induced fields can be significant (Rogers & Showman 2014;Rogers & Komacek 2014;Rogers & McElwaine 2017), which means winds could decrease faster with equilibrium temperature than implied by Equation (14).…”

Section: Evaluating Drag Mechanisms With Observationsmentioning

confidence: 99%

Atmospheric Circulations of Hot Jupiters as Planetary Heat Engines

Koll

Komacek

2018

ApJ

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“…As in Perez-Becker & Showman (2013), they showed that the combined effects of increasing relative efficacy of radiative cooling and increasing drag strength can explain the increase in dayside-nightside temperature contrast with increasing equilibrium temperature, as both mechanisms damp wave adjustment processes. This drag is likely due to either Lorentz forces in an ionized atmosphere threaded by a dipolar magnetic field (Perna et al 2010;Batygin et al 2013;Rauscher & Menou 2013;Rogers & Komacek 2014;Rogers & Showman 2014) or smallscale instabilities (Li & Goodman 2010;Youdin & Mitchell 2010;Fromang et al 2016), including shocks, which largely are expected to occur on the dayside of the planet (Heng 2012;Fromang et al 2016). However, Komacek & Showman (2016) found that drag only affects dayside-nightside temperature differences if it occurs on a characteristic timescale much shorter than the rotation period of the planet.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

Komacek

Showman

Tan

2017

ApJ

149

183

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The full-phase infrared light curves of low-eccentricity hot Jupiters show a trend of increasing fractional daysidenightside brightness temperature difference with increasing incident stellar flux, both averaged across the infrared and in each individual wavelength band. The analytic theory of Komacek & Showman shows that this trend is due to the decreasing ability with increasing incident stellar flux of waves to propagate from day to night and erase temperature differences. Here, we compare the predictions of this theory with observations, showing that it explains well the shape of the trend of increasing dayside-nightside temperature difference with increasing equilibrium temperature. Applied to individual planets, the theory matches well with observations at high equilibrium temperatures but, for a fixed photosphere pressure of 100 mbar, systematically underpredicts the dayside-nightside brightness temperature differences at equilibrium temperatures less than 2000 K. We interpret this as being due to the effects of a process that moves the infrared photospheres of these cooler hot Jupiters to lower pressures. We also utilize general circulation modeling with double-gray radiative transfer to explore how the circulation changes with equilibrium temperature and drag strengths. As expected from our theory, the dayside-nightside temperature differences from our numerical simulations increase with increasing incident stellar flux and drag strengths. We calculate model phase curves using our general circulation models, from which we compare the broadband infrared offset from the substellar point and dayside-nightside brightness temperature differences against observations, finding that strong drag or additional effects (e.g., clouds and/or supersolar metallicities) are necessary to explain many observed phase curves.

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“…More realistically, the morphology of the equatorial jet may not lead to a perfect hemispherical separation of aerosol versusnon-aerosol-dominated segments of the terminator. For example, magnetic effects, which are expected to influence the most highly irradiated planets and are typically not self-consistently included in GCMs, could alter the magnitude and morphology of atmospheric winds (Rauscher & Menou 2013;Rogers & Komacek 2014). Additionally, GCMs that include cloud tracer particles qualitatively predict a non-uniform spatial distribution of aerosols in exoplanet atmospheres (Parmentier et al 2013;Charnay et al 2015).…”

Section: Resultsmentioning

confidence: 99%

An Observational Diagnostic for Distinguishing between Clouds and Haze in Hot Exoplanet Atmospheres

Kempton

Bean

Parmentier

2017

ApJL

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The nature of aerosols in hot exoplanet atmospheres is one of the primary vexing questions facing the exoplanet field. The complex chemistry, multiple formation pathways, and lack of easily identifiable spectral features associated with aerosols make it especially challenging to constrain their key properties. We propose a transmission spectroscopy technique to identify the primary aerosol formation mechanism for the most highly irradiated hot Jupiters (HIHJs). The technique is based on the expectation that the two key types of aerosolsphotochemically generated hazes and equilibrium condensate clouds-are expected to form and persist in different regions of a highly irradiated planet's atmosphere. Haze can only be produced on the permanent daysides of tidally locked hot Jupiters, and will be carried downwind by atmospheric dynamics to the evening terminator (seen as the trailing limb during transit). Clouds can only form in cooler regions on the nightside and morning terminator of HIHJs (seen as the leading limb during transit). Because opposite limbs are expected to be impacted by different types of aerosols, ingress and egress spectra, which primarily probe opposing sides of the planet, will reveal the dominant aerosol formation mechanism. We show that the benchmark HIHJ, WASP-121b, has a transmission spectrum consistent with partial aerosol coverage and that ingress-egress spectroscopy would constrain the location and formation mechanism of those aerosols. In general, using this diagnostic we find that observations with the James Webb Space Telescope and potentially with the Hubble Space Telescope should be able to distinguish between clouds and haze for currently known HIHJs.

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Magnetic Effects in Hot Jupiter Atmospheres

Cited by 134 publications

References 52 publications

Atmospheric Circulations of Hot Jupiters as Planetary Heat Engines

Atmospheric Circulations of Hot Jupiters as Planetary Heat Engines

Atmospheric Circulation of Hot Jupiters: Dayside–Nightside Temperature Differences. II. Comparison with Observations

An Observational Diagnostic for Distinguishing between Clouds and Haze in Hot Exoplanet Atmospheres

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