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Register a new userCould the Migration of Jupiter have Accelerated the Atmospheric Evolution of Venus?
هل يمكن أن يكاد الهجرة الجوپيرية تسريع تطور الغلاف الجوي لفينوس؟
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في دراسة سبل سكنان الكواكب وتطور الغلاف الجوي الأرضي، يظل الانحدار في ظروف السطح بين الفينوس والأرض مجالاً من البحوث النشطة. بين التأثيرات الذاتية والخارجية على تاريخ المناخ الفينوسي هي التغيرات المؤثرة في المدار الناجمة عن نقل الكواكب العملاقة التي تحمل كل من الإشعاع الواقع والتسخين المثلج. هنا، نقدم نتائج دراسة تطرق لتأثير موقع اليوبيتر على المعلمات المدارية للفينوس والسيناريوهات المحتملة لخسارة الماء الناجمة عن ذلك. تظهر تحليلات الديناميكا الخاصة بنا أن العديد من سيناريوهات نقل اليوبيتر المحتملة قد أدت إلى نسب مؤولات مدارية للفينوس تصل إلى 0.31. نقيم آثار الإشعاع المؤول المرتفع، بما في ذلك الإشعاع الحراري السطحي والإشعاع الضوئي المتغير المتوقع من الشمس الضعيفة الشابة. وتظهر الحسابات لوقت التجديد المثلج ان نسبة التسخين المثلج المرتفعة مطلوبة لتقليل نسبة الإشعاع المؤول للفينوس إلى القيمة الحالية، مما يدل على وجود مخزون ماء عالي الأولي. كما نقدر آثار نسبة الإشعاع المؤول المرتفعة على فقدان الماء، ونحتسب أن نسبة فقدان الماء قد زادت على الأقل بنسبة 5٪ نسبة إلى السيناريو المدار الدائري. ونحاول التأكيد على أن هذه التغيرات في الإشعاع المؤول للفينوس الشاب قد تسرعت تطور الغلاف الجوي للفينوس بشكل لا مردود إلى حالة الحمام الغابون المشتعل. وقد يزيد وجود الكواكب العملاقة في أنظمة الكواكب الخارجية من المناحي المتوقعة للفينوس المشابهة في تلك الأنظمة.
In the study of planetary habitability and terrestrial atmospheric evolution, the divergence of surface conditions for Venus and Earth remains an area of active research. Among the intrinsic and external influences on the Venusian climate history are orbital changes due to giant planet migration that have both variable incident flux and tidal heating consequences. Here, we present the results of a study that explores the effect of Jupiters location on the orbital parameters of Venus and subsequent potential water loss scenarios. Our dynamical simulations show that various scenarios of Jovian migration could have resulted in orbital eccentricities for Venus as high as 0.31. We quantify the implications of the increased eccentricity, including tidal energy, surface energy flux, and the variable insolation flux expected from the faint young Sun. The tidal circularization timescale calculations demonstrate that a relatively high tidal dissipation factor is required to reduce the eccentricity of Venus to the present value, which implies a high initial water inventory. We further estimate the consequences of high orbital eccentricity on water loss, and estimate that the water loss rate may have increased by at least $sim$5% compared with the circular orbit case as a result of orbital forcing. We argue that these eccentricity variations for the young Venus may have accelerated the atmospheric evolution of Venus towards the inevitable collapse of the atmosphere into a runaway greenhouse state. The presence of giant planets in exoplanetary systems may likewise increase the expected rate of Venus analogs in those systems.
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We present broad-band photometry of 30 planetary transits of the ultra-hot Jupiter KELT-16b, using five medium-class telescopes. The transits were monitored through standard B, V, R, I filters and four were simultaneously observed from different places, for a total of 36 new light curves. We used these new photometric data and those from the TESS space telescope to review the main physical properties of the KELT-16 planetary system. Our results agree with previous measurements but are more precise. We estimated the mid-transit times for each of these transits and combined them with others from the literature to obtain 69 epochs, with a time baseline extending over more than four years, and searched for transit time variations. We found no evidence for a period change, suggesting a lower limit for orbital decay at 8 Myr, with a lower limit on the reduced tidal quality factor of $Q^{prime}_{star}>(1.9 pm 0.8) times 10^5$ with $95%$ confidence. We built up an observational, low-resolution transmission spectrum of the planet, finding evidence of the presence of optical absorbers, although with a low significance. Using TESS data, we reconstructed the phase curve finding that KELT-16b has a phase offset of $25.25 pm 14.03$ $^{circ}$E, a day- and night-side brightness temperature of $3190 pm 61$ K and $2668 pm 56$ K, respectively. Finally, we compared the flux ratio of the planet over its star at the TESS and Spitzer wavelengths with theoretical emission spectra, finding evidence of a temperature inversion in the planets atmosphere, the chemical composition of which is preferably oxygen-rich rather than carbon-rich.
The presence of the ancient valley networks on Mars indicates that the climate at 3.8 Ga was warm enough to allow substantial liquid water to flow on the martian surface for extended periods of time. However, the mechanism for producing this warming continues to be debated. One hypothesis is that Mars could have been kept warm by global cirrus cloud decks in a CO2-H2O atmosphere containing at least 0.25 bar of CO2 (Urata and Toon, 2013). Initial warming from some other process, e.g., impacts, would be required to make this model work. Those results were generated using the CAM 3-D global climate model. Here, we use a single-column radiative-convective climate model to further investigate the cirrus cloud warming hypothesis. Our calculations indicate that cirrus cloud decks could have produced global mean surface temperatures above freezing, but only if cirrus cloud cover approaches ~75 - 100% and if other cloud properties (e.g., height, optical depth, particle size) are chosen favorably. However, at more realistic cirrus cloud fractions, or if cloud parameters are not optimal, cirrus clouds do not provide the necessary warming, suggesting that other greenhouse mechanisms are needed.
Kepler-13Ab (= KOI-13.01) is a unique transiting hot Jupiter. It is one of very few known short-period planets orbiting a hot A-type star, making it one of the hottest planets currently known. The availability of Kepler data allows us to measure the planets occultation (secondary eclipse) and phase curve in the optical, which we combine with occultations observed by warm Spitzer at 4.5 mic and 3.6 mic and a ground-based occultation observation in the Ks band (2.1 mic). We derive a day-side hemisphere temperature of 2,750 +- 160 K as the effective temperature of a black body showing the same occultation depths. Comparing the occultation depths with one-dimensional planetary atmosphere models suggests the presence of an atmospheric temperature inversion. Our analysis shows evidence for a relatively high geometric albedo, Ag= 0.33 +0.04 -0.06. While measured with a simplistic method, a high Ag is supported also by the fact that the one-dimensional atmosphere models underestimate the occultation depth in the optical. We use stellar spectra to determine the dilution, in the four wide bands where occultation was measured, due to the visual stellar binary companion 1.15 +- 0.05 away. The revised stellar parameters measured using these spectra are combined with other measurements leading to revised planetary mass and radius estimates of Mp = 4.94 - 8.09 Mjup and Rp = 1.406 +- 0.038 Rjup. Finally, we measure a Kepler mid-occultation time that is 34.0 +- 6.9 s earlier than expected based on the mid-transit time and the delay due to light travel time, and discuss possible scenarios.
The competition between the torques induced by solid and thermal tides drives the rotational dynamics of Venus-like planets and super-Earths orbiting in the habitable zone of low-mass stars. The tidal responses of the atmosphere and telluric core are related to their respective physical properties and strongly depend on the tidal frequency. The resulting torque determines the possible equilibrium states of the planets spin. We compute here an analytic expression for the total tidal torque exerted on a Venus-like planet. This expression is used to characterize the equilibrium rotation of the body. Close to the star, the solid tide dominates. Far from it, the thermal tide drives the rotational dynamics of the planet. The transition regime corresponds to the habitable zone, where prograde and retrograde equilibrium states appear. We demonstrate the strong impact of the atmospheric properties and of the rheology of the solid part on the rotational dynamics of Venus-like planets, highlighting the key role played by dissipative mechanisms in the stability of equilibrium configurations.
Type-II migration of giant planets has a speed proportional to the discs viscosity for values of the alpha viscosity parameter larger than 1.e-4 . At lower viscosities previous studies, based on 2D simulations have shown that migration can be very chaotic and often characterized by phases of fast migration. The reason is that in low-viscosity discs vortices appear due to the Rossby-wave instability at the edges of the gap opened by the planet. Migration is then determined by vortex-planet interactions. Our aim is to study migration in low viscosity 3D discs. We performed numerical simulations using 2D (including self-gravity) and 3D codes. After selecting disc masses for which self-gravity is not important, 3D simulations without self-gravity can be safely used. In our nominal simulation only numerical viscosity is present. We then performed simulations with prescribed viscosity to assess the threshold below which the new migration processes appear. We show that for alpha viscosity <= 1.e-5 two migration modes are possible which differ from classical Type-II migration, in the sense that they are not proportional to the discs viscosity. The first occurs when the gap opened by the planet is not very deep. This occurs in 3D simulations and/or when a big vortex forms at the outer edge of the planetary gap, diffusing material into the gap. We call this type of migration vortex-driven migration. This migration is very slow and cannot continue indefinitely, because eventually the vortex dissolves. The second migration mode occurs when the gap is deep so that the planets eccentricity grows to a value ~0.2 due to inefficient eccentricity damping by corotation resonances. This second, faster migration mode appears to be typical of 2D models in discs with slower damping of temperatures perturbations.
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