We investigate 3D atmosphere dynamics for tidally locked terrestrial planets with an Earth-like atmosphere and irradiation for different rotation periods (P
rot = 1–100 d) and planet sizes (R
...P = 1–2R
Earth) with unprecedented fine detail. We could precisely identify three climate state transition regions that are associated with phase transitions in standing tropical and extratropical Rossby waves. We confirm that the climate on fast-rotating planets may assume multiple states (P
rot ≤ 12 d for R
P = 2R
Earth). Our study is, however, the first to identify the type of planetary wave associated with different climate states: the first state is dominated by standing tropical Rossby waves with fast equatorial superrotation. The second state is dominated by standing extratropical Rossby waves with high-latitude westerly jets with slower wind speeds. For very fast rotations (P
rot ≤ 5 d for R
P = 2R
Earth), we find another climate state transition, where the standing tropical and extratropical Rossby wave can both fit on the planet. Thus, a third state with a mixture of the two planetary waves becomes possible that exhibits three jets. Different climate states may be observable, because the upper atmosphere's hotspot is eastward shifted with respect to the substellar point in the first state, westward shifted in the second state and the third state shows a longitudinal ‘smearing’ of the spot across the substellar point. We show, furthermore, that the largest fast-rotating planet in our study exhibits atmosphere features known from hot Jupiters like fast equatorial superrotation and a temperature chevron in the upper atmosphere.
AbstractStratosphere circulation is important to interpret abundances of photochemically produced compounds like ozone which we aim to observe to assess habitability of exoplanets. We thus ...investigate a tidally locked ExoEarth scenario for TRAPPIST-1b, TRAPPIST-1d, Proxima Centauri b and GJ 667 C f with a simplified 3D atmosphere model and for different stratospheric wind breaking assumptions.These planets are representatives for different circulation regimes for orbital periods: Porb = 1-100 d. The circulation of exoplanets with Porb ≤ 25 d can be dominated by the standing tropical Rossby wave in the troposphere and also in the stratosphere: It leads to a strong equatorial eastward wind jet and to an 'Anti-Brewer-Dobson'-circulation that confines airmasses to the stratospheric equatorial region. Thus, the distribution of photochemically produced species and aerosols may be limited to an 'equatorial transport belt'. In contrast, planets with Porb > 25 d, like GJ 667 C f, exhibit efficient thermally driven circulation in the stratosphere which allows for a day side-wide distribution of airmasses.The influence of the standing tropical Rossby waves on tidally locked ExoEarths with Porb ≤ 25 d can, however, be circumvented with deep stratospheric wind breaking alone - allowing for equator-to-pole transport like on Earth. For planets with 3 ≤ Porb ≤ 6 d, the extratropical Rossby wave acts as an additional safeguard against the tropical Rossby wave in case of shallow wind breaking. Therefore, TRAPPIST-1d is less prone to have an equatorial transport belt in the stratosphere than Proxima Centauri b.Even our Earth model shows an equatorial wind jet, if stratosphere wind breaking is inefficient.
Context.
The method of gyrochronology relates the age of its star to its rotation period. However, recent evidence of deviations from gyrochronology relations has been reported in the literature.
...Aims.
We study the influence of tidal interaction between a star and its companion on the rotation velocity of the star to explain peculiar stellar rotation velocities.
Methods.
We followed the interaction of a star and its planet using a comprehensive numerical framework that combines tidal friction, magnetic braking, planet migration, and detailed stellar evolution models from the GARSTEC grid. We focus on close-in companions from 1 to 20
M
Jup
orbiting low-mass (0.8 − 1
M
⊙
) main-sequence stars with a broad metallicity of Fe/H = − 1 up to solar.
Results.
Our simulations suggest that the dynamical interaction between a star and its companion can have different outcomes that depend on the initial semi-major axis and the mass of the planet, as well as on the mass and metallicity of its host star. In most cases, especially in the case of planet engulfment, we find a catastrophic increase in stellar rotation velocity from 1 kms
−1
to over 40 kms
−1
while the star is still on the main-sequence. The main prediction of our model is that low-mass main-sequence stars with abnormal rotation velocities should be more common at low-metallicity, as lower Fe/H favours faster planet engulfment, based on the assumption that the occurrence rate of close-in massive planets is similar at all metallicities.
Conclusions.
Our scenario explains peculiar rotation velocities of low-mass main-sequence stars by the tidal interaction between the star and its companion. Current observational samples are too narrow and incomplete, and, thus, they are not sufficient for our model to be tested.
Context . Eccentric exoplanets offer an opportunity to study the response of an atmosphere to changing thermal forcing and the robustness of the super-rotating equatorial jet seen on tidally locked ...hot Jupiters. However, the atmospheric dynamics on eccentric planets strongly depend on the planetary rotation period, which is difficult to constrain observationally. The ringing phenomenon, whereby the observed emission increases and decreases after the periastron passage as the flash-heated hemisphere rotates into and out of view, can provide a tight constraint on rotation. Aims . We studied five highly eccentric transiting exoplanets HAT-P-2 b, HD 80606 b, TOI-3362 b, TOI-4127 b and HD 17156 b to find which displays strong ringing signals that are sufficiently strong for the James Webb Space Telescope (JWST) to detect. Methods . We implemented the treatment of eccentricity and non-synchronous rotation in the non-grey climate model expeRT/MITgcm and generated synthetic light curves. Results . We find four detectable ringing peaks on HD 80606 b and some undetectable ringing on TOI-4127 b and HD 17156 b. The lack of clouds, photo-chemistry and obliquity in our models may have led us to overestimate the amplitude of the ringing however. The strength of the ringing signal is mostly determined by the eccentricity, planetary rotation period, planet-to-star radius ratio and apparent magnitude of the system. We searched for more exoplanets that could show ringing but found no candidates as promising as HD 80606 b. Conclusions . We recommend prioritising HD 80606 b as a target for ringing with JWST. A baseline of five days after the periastron passage would capture three ringing peaks, which is sufficient to tightly constrain the planetary rotation period. An extension to seven days would add a fourth peak, which would allow us to verify the rotation period.
We investigate how nightside cooling and surface friction affect surface temperatures and large-scale circulation for tidally locked Earth-like planets. For each scenario, we vary the orbital period ...between P
rot = 1 and 100 d and capture changes in climate states. We find drastic changes in climate states for different surface friction scenarios. For very efficient surface friction (t
s,fric = 0.1 d), the simulations for short rotation periods (P
rot ≤ 10 d) show predominantly standing extratropical Rossby waves. These waves lead to climate states with two high-latitude westerly jets and unperturbed meridional direct circulation. In most other scenarios, simulations with short rotation periods exhibit instead dominance by standing tropical Rossby waves. Such climate states have a single equatorial westerly jet, which disrupts direct circulation. Experiments with weak surface friction (t
s,fric = 10–100 d) show decoupling between surface temperatures and circulation, which leads to strong cooling of the nightside. The experiment with t
s,fric = 100 d assumes climate states with easterly flow (retrograde rotation) for medium and slow planetary rotations P
rot = 12–100 d. We show that an increase of nightside cooling efficiency by one order of magnitude compared to the nominal model leads to a cooling of the nightside surface temperatures by 80–100 K. The dayside surface temperatures only drop by 25 K at the same time. The increase in thermal forcing suppresses the formation of extratropical Rossby waves on small planets (R
P = 1R
Earth) in the short rotation period regime (P
rot ≤ 10 d).
Radiative equilibrium temperatures are calculated for the troposphere of a tidally locked Super-Earth based on a simple greenhouse model, using Solar system data as a guideline. These temperatures ...provide in combination with a Newtonian relaxation scheme thermal forcing for a 3D atmosphere model using the dynamical core of the Massachusetts Institute of Technology global circulation model. Our model is of the same conceptional simplicity than the model of Held & Suarez and is thus computationally fast. Furthermore, because of the coherent, general derivation of radiative equilibrium temperatures, our model is easily adaptable for different planets and atmospheric scenarios. As a case study relevant for Super-Earths, we investigate a Gl581g-like planet with Earth-like atmosphere and irradiation and present results for two representative rotation periods of P
rot = 10 d and P
rot = 36.5 d. Our results provide proof of concept and highlight interesting dynamical features for the rotating regime 3 < P
rot < 100 d, which was shown by Edson et al. to be an intermediate regime between equatorial superrotation and divergence. We confirm that the P
rot = 10 d case is more dominated by equatorial superrotation dynamics than the P
rot = 36.5 d case, which shows diminishing influence of standing Rossby–Kelvin waves and increasing influence of divergence at the top of the atmosphere. We argue that this dynamical regime change relates to the increase in Rossby deformation radius, in agreement with previous studies. However, we also pay attention to other features that are not or only in partial agreement with other studies, like, e.g. the number of circulation cells and their strength, the role and extent of thermal inversion layers, and the details of heat transport.
Context.
Ultra-hot Jupiters are the hottest exoplanets that have been discovered so far. Observations begin to provide insight into the composition of their extended atmospheres and their chemical ...day/night asymmetries. Both are strongly affected by cloud formation.
Aims.
We explore trends in cloud properties for a sample of five giant gas planets: the hot gas giant WASP-43b and the four ultra-hot Jupiters (UHJs) WASP-18b, HAT-P-7b, WASP-103b, and WASP-121b. This provides a reference frame for cloud properties for the JWST targets WASP-43b and WASP-121b. We further explore chemically inert tracers to observe geometrical asymmetries of UHJs and if the location of the inner boundary of a 3D global circulation model (3D GCM) matters for the clouds that form.
Methods.
A homogeneous set of 3D GCM results was used as input for a kinetic cloud formation code to evaluate the cloud opacity and gas parameters such as C/O, mean molecular weight, and degree of ionisation. We cast our results in terms of integrated quantities to enable a global comparison between the sample planets.
Results.
The large day/night temperature differences of UHJs cause the following chemical asymmetries: cloud-free days but cloudy nights, atomic versus molecular gases and their different mean molecular weights, deep thermal ionospheres versus low-ionised atmospheres, and undepleted versus enhanced C/O. WASP-18b, as the heaviest planet in the sample, has the lowest global C/O.
Conclusions.
The global climate may be considered as similar amongst UHJs, but different to that of hot gas giants. The local weather, however, is individual for each planet since the local thermodynamic conditions, and hence the local cloud and gas properties, differ. The morning and the evening terminator of UHJs will carry signatures of their strong chemical asymmetry such that ingress and egress asymmetries can be expected. An increased C/O ratio is a clear sign of cloud formation, making cloud modelling a necessity when utilising C/O (or other mineral ratios) as a tracer for planet formation. The changing geometrical extension of the atmosphere from the day to the nightside may be probed through chemically inert species such as helium. Ultra-hot Jupiters are likely to develop deep atmospheric ionospheres which may impact the atmosphere dynamics through magneto-hydrodynamic processes.
Context.
Theoretical studies predict the presence of thermal inversions in the atmosphere of highly irradiated gas giant planets. Recent observations have identified these inversion layers. However, ...the role of different chemical species in their formation remains unclear.
Aims.
We search for the signature of the thermal inversion agents TiO and Fe in the dayside emission spectrum of the ultra-hot Jupiter WASP-33b.
Methods.
The spectra were obtained with CARMENES and HARPS-N, covering different wavelength ranges. Telluric and stellar absorption lines were removed with
SYSREM
. We cross-correlated the residual spectra with model spectra to retrieve the signals from the planetary atmosphere.
Results.
We find evidence for TiO at a significance of 4.9σ with CARMENES. The strength of the TiO signal drops close to the secondary eclipse. No TiO signal is found with HARPS-N. An injection-recovery test suggests that the TiO signal is below the detection level at the wavelengths covered by HARPS-N. The emission signature of Fe is detected with both instruments at significance levels of 5.7σ and 4.5σ, respectively. By combining all observations, we obtain a significance level of 7.3σ for Fe. We find the TiO signal at
K
p
= 248.0
−2.5
+2.0
km s
−1
, which is in disagreement with the Fe detection at
K
p
= 225.0
−3.5
+4.0
km s
−1
. The
K
p
value for Fe is in agreement with prior investigations. The model spectra require different temperature profiles for TiO and Fe to match the observations. We observe a broader line profile for Fe than for TiO.
Conclusions.
Our results confirm the existence of a temperature inversion layer in the planetary atmosphere. The observed
K
p
offset and different strengths of broadening in the line profiles suggest the existence of a TiO-depleted hot spot in the planetary atmosphere.
exotrans is a software package developed by the Department of Planetary Research of the Rheinisches Institut für Umweltforschung (RIU-PF) at Cologne University for detecting transit signals from ...extrasolar planets in stellar light curves. exotrans is used very successfully by RIU-PF within the CoRoT mission. The software package uses two different filter algorithms for pre-whitening and noise reduction (harmonic and trend filtering). Three different box-fitting least-squares algorithms (BLS) are applied in order to extract a potential transit signal from the light curves. The performance of each filter-BLS-algorithm combination on real CoRoT data is presented and compared with other methods used by the CoRoT team.
ABSTRACT exotrans is a software package developed by the Department of Planetary Research of the Rheinisches Institut für Umweltforschung (RIU-PF) at Cologne University for detecting transit signals ...from extrasolar planets in stellar light curves. exotrans is used very successfully by RIU-PF within theCoRoT mission. The software package uses two different filter algorithms for pre-whitening and noise reduction (harmonic and trend filtering). Three different box-fitting least-squares algorithms (BLS) are applied in order to extract a potential transit signal from the light curves. The performance of each filter-BLS-algorithm combination on realCoRoT data is presented and compared with other methods used by theCoRoT team. PUBLICATION ABSTRACT
PDF
