The cause of hot-Jupiter radius inflation, where giant planets with > 1000 K are significantly larger than expected, is an open question and the subject of many proposed explanations. Many of these ...hypotheses postulate an additional anomalous power that heats planets' convective interiors, leading to larger radii. Rather than examine these proposed models individually, we determine what anomalous powers are needed to explain the observed population's radii, and consider which models are most consistent with this. We examine 281 giant planets with well-determined masses and radii and apply thermal evolution and Bayesian statistical models to infer the anomalous power as a fraction of (and varying with) incident flux ϵ(F) that best reproduces the observed radii. First, we observe that the inflation of planets below about M = 0.5 MJ appears very different than their higher-mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. As such, we exclude planets below this threshold. Next, we show with strong significance that ϵ(F) increases with toward a maximum of ∼2.5% at Teq 1500 K, and then decreases as temperatures increase further, falling to ∼0.2% at Teff = 2500 K. This high-flux decrease in inflation efficiency was predicted by the Ohmic dissipation model of giant planet inflation but not other models. We also show that the thermal tides model predicts far more variance in radii than is observed. Thus, our results provide evidence for the Ohmic dissipation model and a functional form for ϵ(F) that any future theories of hot-Jupiter radii can be tested against.
THE MASS-METALLICITY RELATION FOR GIANT PLANETS Thorngren, Daniel P.; Fortney, Jonathan J.; Murray-Clay, Ruth A. ...
Astrophysical journal/The Astrophysical journal,
11/2016, Letnik:
831, Številka:
1
Journal Article
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ABSTRACT Exoplanet discoveries of recent years have provided a great deal of new data for studying the bulk compositions of giant planets. Here we identify 47 transiting giant planets (20 M⊕ < M < 20 ...MJ) whose stellar insolations are low enough (F* < 2 × 108 erg s−1 cm−2, or roughly Teff < 1000) that they are not affected by the hot-Jupiter radius inflation mechanism(s). We compute a set of new thermal and structural evolution models and use these models in comparison with properties of the 47 transiting planets (mass, radius, age) to determine their heavy element masses. A clear correlation emerges between the planetary heavy element mass Mz and the total planet mass, approximately of the form . This finding is consistent with the core-accretion model of planet formation. We also study how stellar metallicity Fe/H affects planetary metal-enrichment and find a weaker correlation than has previously been reported from studies with smaller sample sizes. We confirm a strong relationship between the planetary metal-enrichment relative to the parent star Zplanet/Zstar and the planetary mass, but see no relation in Zplanet/Zstar with planet orbital properties or stellar mass. The large heavy element masses of many planets (>50 M⊕) suggest significant amounts of heavy elements in H/He envelopes, rather than cores, such that metal-enriched giant planet atmospheres should be the rule. We also discuss a model of core-accretion planet formation in a one-dimensional disk and show that it agrees well with our derived relation between mass and Zplanet/Zstar.
Creating the Radius Gap without Mass Loss Lee, Eve J.; Karalis, Amalia; Thorngren, Daniel P.
Astrophysical journal/The Astrophysical journal,
12/2022, Letnik:
941, Številka:
2
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Abstract
The observed exoplanet population features a gap in the radius distribution that separates the smaller super-Earths (≲1.7 Earth radii) from the larger sub-Neptunes (∼1.7–4 Earth radii). ...While mass-loss theories can explain many of the observed features of this radius valley, it is difficult to reconcile them with the potentially rising population of terrestrials beyond orbital periods of ∼30 days. We investigate the ability of gas accretion during the gas-poor phase of disk evolution to reproduce both the location of the observed radius gap and the existence of long-period terrestrial planets. Updating the analytic scaling relations of gas accretion rate accounting for the shrinking of the bound radius by hydrodynamic effects and deriving a more realistic disk temperature profile, we find that the late-stage gas accretion alone is able to carve out the observed radius gap, with slopes
R
gap
∝
P
−0.096
and
R
gap
∝
M
⋆
0.15
for top-heavy; and
R
gap
∝
P
−0.089
and
R
gap
∝
M
⋆
0.22
for bottom-heavy core mass distributions, in good agreement with observations. The general morphology of the primordial radius gap is stable against a range of disk gas density and disk accretion rate with the latter affecting mostly the population of large planets (≳3–4
R
⊕
). The peaks and valleys in the radius distribution were likely set in place primordially while post-formation mass loss further tunes the exoplanetary population. We provide potential observational tests that may be possible with TESS, PLATO, and Roman Space Telescope.
A large fraction of known Jupiter-like exoplanets are inflated as compared to Jupiter. These "hot" Jupiters orbit close to their parent star and are bombarded with intense starlight. Many theories ...have been proposed to explain their radius inflation and several suggest that a small fraction of the incident starlight is injected into the planetary interior, which helps to puff up the planet. How will such energy injection affect the planetary dynamo? In this Letter, we estimate the surface magnetic field strength of hot Jupiters using scaling arguments that relate energy available in planetary interiors to the dynamo-generated magnetic fields. We find that if we take into account the energy injected in the planetary interior that is sufficient to inflate hot Jupiters to observed radii, then the resulting dynamo should be able generate magnetic fields that are more than an order of magnitude stronger than the Jovian values. Our analysis highlights the potential fundamental role of the stellar light in setting the field strength in hot Jupiters.
Abstract
The hot Saturn population exhibits a boundary in mass–radius space, such that no planets are observed at a density less than ∼0.1 g cm
−3
. Yet, planet interior structure models can readily ...construct such objects as the natural result of radius inflation. Here, we investigate the role X-ray and extreme UV irradiation (XUV)-driven mass loss plays in sculpting the density boundary by constructing interior structure models that include radius inflation, photoevaporative mass loss, and a simple prescription of Roche lobe overflow. We demonstrate that planets puffier than ∼0.1 g cm
−3
experience a runaway mass loss caused by adiabatic radius expansion as the gas layer is stripped away, providing a good explanation of the observed edge in mass–radius space. The process is also visible in the radius–period and mass–period spaces, though smaller, high-bulk-metallicity planets can still survive at short periods, preserving a partial record of the population distribution at formation.
Reinflation of Warm and Hot Jupiters Komacek, Thaddeus D.; Thorngren, Daniel P.; Lopez, Eric D. ...
Astrophysical journal/The Astrophysical journal,
04/2020, Letnik:
893, Številka:
1
Journal Article
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Understanding the anomalous radii of many transiting hot gas-giant planets is a fundamental problem of planetary science. Recent detections of reinflated warm Jupiters orbiting post-main-sequence ...stars and the reinflation of hot Jupiters while their host stars evolve on the main sequence may help constrain models for the anomalous radii of hot Jupiters. In this work, we present evolution models studying the reinflation of gas giants to determine how varying the depth and intensity of deposited heating affects both main-sequence reinflation of hot Jupiters and post-main-sequence reinflation of warm Jupiters. We find that deeper heating is required to reinflate hot Jupiters than is needed to suppress their cooling, and that the timescale of reinflation decreases with increasing heating rate and depth. We find a strong degeneracy between heating rate and depth, with either strong shallow heating or weak deep heating providing an explanation for main-sequence reinflation of hot Jupiters. This degeneracy between heating rate and depth can be broken in the case of post-main-sequence reinflation of warm Jupiters, as the inflation must be rapid to occur within post-main-sequence evolution timescales. We also show that the dependence of heating rate on the incident stellar flux inferred from the sample of hot Jupiters can explain reinflation of both warm and hot Jupiters. TESS will obtain a large sample of warm Jupiters orbiting post-main-sequence stars, which will help to constrain the mechanism(s) causing the anomalous radii of gas-giant planets.
The atmospheric pressure-temperature profiles for transiting giant planets cross a range of chemical transitions. Here we show that the particular shapes of these irradiated profiles for warm giant ...planets below ∼1300 K lead to striking differences in the behavior of nonequilibrium chemistry compared to brown dwarfs of similar temperatures. Our particular focus is H2O, CO, CH4, CO2, and NH3 in Jupiter- and Neptune-class planets. We show that the cooling history of a planet, which depends most significantly on planetary mass and age, can have a dominant effect on abundances in the visible atmosphere, often swamping trends one might expect based on Teq alone. The onset of detectable CH4 in spectra can be delayed to lower Teq for some planets compared to equilibrium, or pushed to higher Teq. The detectability of NH3 is typically enhanced compared to equilibrium expectations, which is opposite to the brown dwarf case. We find that both CH4 and NH3 can become detectable at around the same Teq (at Teq values that vary with mass and metallicity), whereas these "onset" temperatures are widely spaced for brown dwarfs. We suggest observational strategies to search for atmospheric trends and stress that nonequilibrium chemistry and clouds can serve as probes of atmospheric physics. As examples of atmospheric complexity, we assess three Neptune-class planets, GJ 436b, GJ 3470b, and WASP-107, all around Teq = 700 K. Tidal heating due to eccentricity damping in all three planets heats the deep atmosphere by thousands of degrees and may explain the absence of CH4 in these cool atmospheres. Atmospheric abundances must be interpreted in the context of physical characteristics of the planet.
Abstract
The unexpectedly large radii of hot Jupiters are a longstanding mystery whose solution will provide important insights into their interior physics. Many potential solutions have been ...suggested, which make diverse predictions about the details of inflation. In particular, although any valid model must allow for maintaining large planetary radii, only some allow for radii to increase with time. This reinflation process would potentially occur when the incident flux on the planet is increased. In this work, we examine the observed population of hot Jupiters to see if they grow as their parent stars brighten along the main sequence. We consider the relation between radius and other observables, including mass, incident flux, age, and fractional age (age over main-sequence lifetime), and show that main-sequence brightening is often sufficient to produce detectable reinflation. We further argue that these provide strong evidence for the relatively rapid reinflation of giant planets, and discuss the implications for proposed heating mechanisms. In our population analysis we also find evidence for a “delayed cooling effect,” wherein planets cool and contract far more slowly than expected. While not capable of explaining the observed radii alone, it may represent an important component of the effect. Finally, we identify a weak negative relationship between stellar metallicity and planet radius that is presumably the result of enhanced planetary bulk metallicity around metal-rich stars and has important implications for planet formation theory.
Abstract
We conducted the first dedicated search for signatures of exoplanet–exomoon interactions using the Giant Metrewave Radio Telescope (GMRT) as part of the radio-loud exoplanet-exomoon survey. ...Due to stellar tidal heating, irradiation, and subsequent atmospheric escape, candidate “exo-Io” systems are expected to emit up to 10
6
times more plasma flux than the Jupiter-Io DC circuit. This can induce detectable radio emission from the exoplanet-exomoon system. We analyze three “exo-Io” candidate stars: WASP-49, HAT-P 12, and HD 189733. We perform 12 hr phase-curve observations of WASP-49b at 400 MHz during primary & secondary transit, as well as first & third quadratures achieving a 3
σ
upper limit of 0.18 mJy beam
−1
averaged over four days. HAT-P 12 was observed with GMRT at 150 and 325 MHz. We further analyzed the archival data of HD 189733 at 325 MHz. No emission was detected from the three systems. However, we place strong upper limits on radio flux density. Given that most exo-Io candidates orbit hot Saturns, we encourage more multiwavelength searches (in particular low frequencies) to span the lower range of exoplanet B-field strengths constrained here.
Abstract
Many hot and ultra-hot Jupiters have inflated radii, implying that their interiors retain significant entropy from formation. These hot interiors lead to an enhanced internal heat flux that ...impinges upon the atmosphere from below. In this work, we study the effect of this hot interior on the atmospheric circulation and thermal structure of hot and ultra-hot Jupiters. To do so, we incorporate the population-level predictions from evolutionary models of hot and ultra-hot Jupiters as input for a suite of general circulation models (GCMs) of their atmospheric circulation with varying semimajor axis and surface gravity. We conduct simulations with and without a hot interior, and find that there are significant local differences in temperature of up to hundreds of Kelvin and in wind speeds of hundreds of meters per second or more across the observable atmosphere. These differences persist throughout the parameter regime studied, and are dependent on surface gravity through the impact on photosphere pressure. These results imply that the internal evolution and atmospheric thermal structure and dynamics of hot and ultra-hot Jupiters are coupled. As a result, a joint approach including both evolutionary models and GCMs may be required to make robust predictions for the atmospheric circulation of hot and ultra-hot Jupiters.
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