Scientists have spotted weather systems on a gas giant planet beyond our solar system for the first time ever, and it's definitely out of this world. It's entirely possibly that wild winds are blowing ruby and sapphire clouds on the blazing "hot Jupiter" planet HAT-P-7b over 1,000 light years away.
Researchers used NASA's Kepler space telescope to study the light reflected by the planet 16 times larger than Earth and watch how its atmosphere changed over a period of time.
"HAT-P-7b is a tidally locked planet, with the same side always facing its star. We expect clouds to form on the cold night side of the planet, but they would evaporate quickly on the hot dayside," explains the University of Warwick's Dr. David Armstrong, who led the research. "These results show that strong winds circle the planet, transporting clouds from the night side to the dayside. The winds change speed dramatically, leading to huge cloud formations building up then dying away."
The team noticed that the brightest point on the planet would shift its position, likely due to variable winds and violent storm systems. Because the planet is so much hotter than ours, the scientists had to speculate about what elements could possibly form the "morning" clouds observed at dayside temperatures of 1,700°C, hot enough to melt iron.
Two possibilities are corundum and perovskite. Corundum is the mineral that forms rubies and sapphires on Earth and it would probably make for some colorful clouds being blown around HAT-P-7b.
"Perhaps clouds of ruby are moving around this planet, appearing and disappearing in a stunning display," Armstrong suggests.
Inferring asymmetric limb cloudiness on exoplanets from transit light curves
Authors:
von Paris et al
Abstract:
Clouds have been shown to be present in many exoplanetary atmospheres. Cloud formation modeling predicts considerable inhomogeneities of cloud cover, consistent with optical phase curve observations. However, optical phase curves cannot resolve some existing degeneracies between cloud location and cloud optical properties.
We present a conceptually simple technique to detect inhomogeneous cloud cover on exoplanets. Such an inhomogeneous cloud cover produces an asymmetric primary transit of the planet in front of the host star. Asymmetric transits produce characteristic residuals compared to a standard symmetric model. Furthermore, bisector spans can be used to determine asymmetries in the transit light curve.
We apply a model of asymmetric transits to the light curves of HAT-P-7b, Kepler-7b and HD209458b and search for possible cloud signatures. The nearly uninterrupted Kepler photometry is particularly well-suited for this method since it allows for a very high time resolution.
We do not find any statistically sound cloud signature in the data of the considered planets. For HAT-P-7b, a tentative detection of an asymmetric cloud cover is found, consistent with analysis of the optical phase curve. Based on Bayesian probability arguments, a symmetric model with an offset in the transit ephemeris remains, however, the most viable model. Still, this work demonstrates that for suitable targets, namely low-gravity planets around bright stars, the method can be used to constrain cloud cover characteristics and is thus a helpful additional tool to study exoplanetary atmospheres.
Spin-orbit alignment of exoplanet systems: ensemble analysis using asteroseismology
Authors:
Campante et al
Abstract:
The angle ψ between a planet's orbital axis and the spin axis of its parent star is an important diagnostic of planet formation, migration, and tidal evolution. We seek empirical constraints on ψ by measuring the stellar inclination is via asteroseismology for an ensemble of 25 solar-type hosts observed with NASA's Kepler satellite. Our results for is are consistent with alignment at the 2-σ level for all stars in the sample, meaning that the system surrounding the red-giant star Kepler-56 remains as the only unambiguous misaligned multiple-planet system detected to date. The availability of a measurement of the projected spin-orbit angle λ for two of the systems allows us to estimate ψ. We find that the orbit of the hot-Jupiter HAT-P-7b is likely to be retrograde (ψ=116.4+30.2−14.7deg), whereas that of Kepler-25c seems to be well aligned with the stellar spin axis (ψ=12.6+6.7−11.0deg). While the latter result is in apparent contradiction with a statement made previously in the literature that the multi-transiting system Kepler-25 is misaligned, we show that the results are consistent, given the large associated uncertainties. Finally, we perform a hierarchical Bayesian analysis based on the asteroseismic sample in order to recover the underlying distribution of ψ. The ensemble analysis suggests that the directions of the stellar spin and planetary orbital axes are correlated, as conveyed by a tendency of the host stars to display large inclination values.
3.6 and 4.5 μm Spitzer Phase Curves of the Highly-Irradiated Hot Jupiters WASP-19b and HAT-P-7b
Authors:
Wong et al
Abstract:
We analyze full-orbit phase curve observations of the transiting hot Jupiters WASP-19b and HAT-P-7b at 3.6 and 4.5 μm obtained using the Spitzer Space Telescope. For WASP-19b, we measure secondary eclipse depths of 0.485%±0.024% and 0.584%±0.029% at 3.6 and 4.5 μm, which are consistent with a single blackbody with effective temperature 2372±60 K. The measured 3.6 and 4.5 μm secondary eclipse depths for HAT-P-7b are 0.156%±0.009% and 0.190%±0.006%, which are well-described by a single blackbody with effective temperature 2667±57 K. Comparing the phase curves to the predictions of one-dimensional and three-dimensional atmospheric models, we find that WASP-19b's dayside emission is consistent with a model atmosphere with no dayside thermal inversion and moderately efficient day-night circulation. We also detect an eastward-shifted hotspot, suggesting the presence of a superrotating equatorial jet. In contrast, HAT-P-7b's dayside emission suggests a dayside thermal inversion and relatively inefficient day-night circulation; no hotspot shift is detected. For both planets, these same models do not agree with the measured nightside emission. The discrepancies in the model-data comparisons for WASP-19b might be explained by high-altitude silicate clouds on the nightside and/or high atmospheric metallicity, while the very low 3.6 μm nightside planetary brightness for HAT-P-7b may be indicative of an enhanced global C/O ratio. We compute Bond albedos of 0 (less than 0.08 at 1σ) and 0.38±0.06 for WASP-19b and HAT-P-7b, respectively. In the context of other planets with thermal phase curve measurements, we show that WASP-19b and HAT-P-7b fit the general trend of decreasing day-night heat recirculation with increasing irradiation.
Inferring heat recirculation and albedo for exoplanetary atmospheres: Comparing optical phase curves and secondary eclipse data
Authors:
von Paris et al
Abstract:
Basic atmospheric properties such as albedo and heat redistribution between day and nightside have been inferred for a number of planets using observations of secondary eclipses and thermal phase curves. Optical phase curves have not yet been used to constrain these atmospheric properties consistently. We re-model previously published phase curves of CoRoT-1b, TrES-2b and HAT-P-7b and infer albedos and recirculation efficiencies. These are then compared to previous estimates based on secondary eclipse data. We use a physically consistent model to construct optical phase curves. This model takes Lambertian reflection, thermal emission, ellipsoidal variations and Doppler boosting into account. CoRoT-1b shows a non-negligible scattering albedo (0.11
Spin-Orbit Angles of Kepler-13Ab and HAT-P-7b from Gravity-Darkened Transit Light Curves
Author:
Masuda
Abstract:
Analysis of the transit light curve deformed by the stellar gravity darkening allows us to photometrically measure both components of the spin-orbit angle ψ, its sky projection λ and inclination of the stellar spin axis i⋆. In this paper, we apply the method to two transiting hot Jupiter systems monitored with the Kepler spacecraft, Kepler-13A and HAT-P-7. For Kepler-13A, we find i⋆=81∘±5∘ and ψ=60∘±2∘ adopting the spectroscopic constraint λ=58.6∘±2.0∘ by Johnson et al. (2014). In our solution, the discrepancy between the above λ and that previously reported by Barnes et al. (2011) is solved by fitting both of the two parameters in the quadratic limb-darkening law. We also report the temporal variation in the orbital inclination of Kepler-13Ab, d|cosiorb|/dt=(−7.0±0.4)×10−6day−1, providing further evidence for the spin-orbit precession in this system. By fitting the precession model to the time series of iorb, λ, and i⋆ obtained with the gravity-darkened model, we constrain the stellar quadrupole moment J2=(6.1±0.3)×10−5 for our new solution, which is several times larger than J2=(1.66±0.08)×10−4 obtained for the previous one. We show that the difference can be observable in the future evolution of λ, thus providing a possibility to test our solution with follow-up observations. The second target, HAT-P-7, is the first F-dwarf star analyzed with the gravity-darkening method. Our analysis points to a nearly pole-on configuration with ψ=101∘±2∘ or 87∘±2∘ and the gravity-darkening exponent β consistent with 0.25. Such an observational constraint on β can be useful for testing the theory of gravity darkening.
Constraining the Oblateness of Kepler Planets
Authors:
Zhu et al
Abstract:
We use Kepler short cadence light curves to constrain the oblateness of planet candidates in the Kepler sample. The transits of rapidly rotating planets that are deformed in shape will lead to distortions in the ingress and egress of their light curves. We report the first tentative detection of an oblate planet outside of the solar system, measuring an oblateness of 0.22±0.11 for the 18 MJ mass brown dwarf Kepler 39b (KOI-423.01). We also provide constraints on the oblateness of the planets (candidates) HAT-P-7b, KOI-686.01, and KOI-197.01 to be less than 0.067, less than 0.251, and less than 0.186, respectively. Using the Q'-values from Jupiter and Saturn, we expect tidal synchronization for the spins of HAT-P-7b, KOI-686.01 and KOI-197.01, and for their rotational oblateness signatures to be undetectable in the current data. The potentially large oblateness of KOI-423.01 (Kepler 39b) suggests that the Q'-value of the brown dwarf needs to be two orders of magnitude larger than that of the solar system gas giants to avoid being tidally spun-down.
Asteroseismic inference on the spin-orbit misalignment and stellar parameters of HAT-P-7
Authors:
Lund et al
Abstract:
The measurement of obliquities in star-planet systems is of great importance for the understanding of planet system formation and evolution. The bright and well studied HAT-P-7 system is intriguing as several Rossiter-McLaughlin (RM) measurements found a large projected obliquity in this system, but it was so far not possible to determine if the orbit is polar and/or retrograde. The goal of this study is to measure the stellar inclination and hereby the full 3D obliquity of the HAT-P-7 system instead of only the 2D projection as measured by the RM effect. In addition we provide an updated set of stellar parameters for the star. We use the full set of available observations from Kepler spanning Q0-Q17 to produce the power spectrum of HAT-P-7. We extract oscillation mode frequencies via an MCMC peak-bagging routine, and use the results from this to estimate the stellar inclination angle. Combining this with the projected obliquity from RM and the inclination of the orbital plane allows us to determine the stellar obliquity. We use asteroseismology to model the star from the extracted frequencies using two different approaches to the modelling where either the MESA or the GARSTEC stellar evolution codes are adopted. Using our updated asteroseismic modelling we find, i.a., the following stellar parameters for HAT-P-7: M=1.51{+0.04}{-0.05}Msun, $R=2.00{+0.01}{-0.02}Rsun, and age = 2.07{+0.28}{-0.23} Gyr. Our asteroseismic modelling offers a high precision on the stellar parameters, for instance is the uncertainty on age of the order ~11%. For the stellar inclination we estimate i_starless than 36.5 deg., which translates to an obliquity between 83 and 111 deg. We find that the planet HAT-P-7b is likely retrograde in its orbit, and that the orbit is close to being polar. The new parameters for the star gives an updated planetary density of 0.65+-0.03 g cm^{-3}, which is lower than previous estimates.
Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry
Authors:
Esteves et al
Absrtact:
We present a comprehensive analysis of planetary phase variations, including possible planetary light offsets, using eighteen quarters of data from the Kepler space telescope. After correcting for systematics, we found fourteen systems with significant detections in each of the phase curve components: planet's phase function, secondary eclipse, Doppler boosting and ellipsoidal variations. We model the full phase curve simultaneously, including primary and secondary transits, and derive albedos, day- and night-side temperatures and planet masses. We find that KOI-13b, with a small eccentricity, is the only planet for which an eccentric orbit is favored. We detect a third harmonic with an amplitude of 1.9 ppm for HAT-P-7b for the first time, and confirm the third harmonic for KOI-13b reported in Esteves et al. (2013): both could be due to their spin-orbit misalignments. We also performed a bootstrap analysis of each of our targets, and conclude that the photometric variations of Kepler-43b are not of planetary origin but instead a result of stellar variability and/or residual systematics. For seven planets, we find that the planetary light peak is offset from the substellar point: of those, the hottest two exhibit shifts eastward or to the evening-side, while the cooler five peak westward or on the morning-side. Our findings dramatically increase the number of Kepler planets with detected planetary light offsets, and provide the first evidence in the Kepler data for a correlation between the peak offset direction and the planet's temperature. Such a correlation could arise if thermal emission dominates light from hotter planets that harbor hot spots shifted to the east, as theoretically predicted, while reflected light dominates cooler planets with clouds westward of the substellar point (i.e. on the morning-side).
Properties of extrasolar planets and their host stars - a case study of HAT-P-7
Authors:
Van Eylen et al
Abstract:
Data from the Kepler satellite (Q0-Q11) are used to study HAT-P-7. The satellite's data are extremely valuable for asteroseismic studies of stars and for observing planetary transits; in this work we do both. An asteroseismic study of the host star improves the accuracy of the stellar parameters derived by Christensen-Dalsgaard et al. (2010), who followed largely the same procedure but based the analysis on only one month of Kepler data. The stellar information is combined with transit observations, phase variations and occultations to derive planetary parameters. In particular, we confirm the presence of ellipsoidal variations as discovered by Welsh et al. (2010), but revise their magnitude, and we revise the occultation depth (Borucki et al. 2009), which leads to different planetary temperature estimates. All other stellar and planetary parameters are now more accurately determined.
