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Register a new userThe Three Dimensional Flow Field Around Planets on Eccentric Orbits
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We investigate the properties of the hydrodynamic flow around eccentric protoplanets and compare them with the often assumed case of a circular orbit. To this end, we perform a set of 3D hydrodynamic simulations of protoplanets with small eccentricities ($eleq 0.1$). We adopt an isothermal equation of state and concentrate resolution on the protoplanet to investigate flows down to the scale of the protoplanets circumplanetary disk (CPD). We find enhanced prograde rotation exterior to the CPD for low planet masses undergoing subsonic eccentric motion. If the eccentricity is made large enough to develop a bow shock, this trend reverses and rotation becomes increasingly retrograde. The instantaneous eccentric flow field is dramatically altered compared to circular orbits. Whereas the latter exhibit a generic pattern of polar inflow and midplane outflow, the flow geometry depends on orbital phase in the eccentric case. For even the modest eccentricities tested here, the dominant source of inflow can come from the midplane instead of the poles. We find that the amount of inflow and outflow increases for higher $e$ and lower protoplanet masses, thereby recycling more gas through the planets Bondi radius. These increased fluxes may increase the pebble accretion rate for eccentric planets up to several times that of the circular orbit rate. In response to eccentric motion, the structure and rotation of the planets bound CPD remains unchanged. Because the CPD regulates the eventual accretion of gas onto the planet, we predict little change to the gas accretion rates between eccentric and circular planets.
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Protoplanets are able to accrete primordial atmospheres when embedded in the gaseous protoplanetary disk. The formation and structure of the proto-atmosphere are subject to the planet--disk environment and orbital effects. Especially, when planets are on eccentric orbits, their relative velocities to the gas can exceed the sound speed. The planets generate atmosphere-stripping bow shocks. We investigate the proto-atmospheres on low-mass planets with eccentric orbits with radiation-hydrodynamics simulations. A 2D radiative model of the proto-atmosphere is established with tabulated opacities for the gas and dust. The solutions reveal large-scale gas recycling inside a bow shock structure. The atmospheres on eccentric planets are typically three to four orders of magnitude less massive than those of planets with circular orbits. Overall, however, a supersonic environment is favorable for planets to keep an early stable atmosphere, rather than harmful, due to the steady gas supply through the recycling flow. We also quantitatively explore how such atmospheres are affected by the relative velocity of the planet to the gas, the planet mass, and the background gas density. Our time-dependent simulations track the orbital evolution of the proto-atmosphere with the planet--disk parameters changing throughout the orbit. Atmospheric properties show oscillatory patterns as the planet travels on an eccentric orbit, with a lag in phase. To sum up, low-mass eccentric planets can retain small proto-atmospheres despite the stripping effects of bow shocks. The atmospheres are always connected to and interacting with the disk gas. These findings provide important insights into the impacts of migration and scattering on planetary proto-atmospheres.
We investigate the resonant rotation of co-orbital bodies in eccentric and planar orbits. We develop a simple analytical model to study the impact of the eccentricity and orbital perturbations on the spin dynamics. This model is relevant in the entire domain of horseshoe and tadpole orbit, for moderate eccentricities. We show that there are three different families of spin-orbit resonances, one depending on the eccentricity, one depending on the orbital libration frequency, and another depending on the pericenters dynamics. We can estimate the width and the location of the different resonant islands in the phase space, predicting which are the more likely to capture the spin of the rotating body. In some regions of the phase space the resonant islands may overlap, giving rise to chaotic rotation.
Doppler measurements of two G-type main-sequence stars, HD210277 and HD168443, reveal Keplerian variations that imply the presence of companions with masses (M sin i) of 1.28 and 5.04 M_Jup and orbital periods of 437 d and 58 d, respectively. The orbits have large eccentricities of e=0.45 and e=0.54, respectively. All 9 known extrasolar planet candidates with a=0.2-2.5 AU have orbital eccentricities greater than 0.1, higher than that of Jupiter (e=0.05). Eccentric orbits may result from gravitational perturbations imposed by other orbiting planets or stars, by passing stars in the dense star-forming cluster, or by the protoplanetary disk. Based on published studies and our near-IR adaptive optics images, HD210277 appears to be a single star. However, HD168443 exhibits a long-term velocity trend consistent with a close stellar companion, as yet undetected directly.
An episode of dynamical instability is thought to have sculpted the orbital structure of the outer solar system. When modeling this instability, a key constraint comes from Jupiters fifth eccentric mode (quantified by its amplitude M55), which is an important driver of the solar systems secular evolution. Starting from commonly-assumed near-circular orbits, the present-day giant planets architecture lies at the limit of numerically generated systems, and M55 is rarely excited to its true value. Here we perform a dynamical analysis of a large batch of artificially triggered instabilities, and test a variety of configurations for the giant planets primordial orbits. In addition to more standard setups, and motivated by the results of modern hydrodynamical simulations of the giant planets evolution within the primordial gaseous disk, we consider the possibility that Jupiter and Saturn emerged from the nebular gas locked in 2:1 resonance with non-zero eccentricities. We show that, in such a scenario, the modern Jupiter-Saturn system represents a typical simulation outcome, and M55 is commonly matched. Furthermore, we show that Uranus and Neptunes final orbits are determined by a combination of the mass in the primordial Kuiper belt and that of an ejected ice giant.
Context. Due to their low transit probability, the long-period planets are, as a population, only partially probed by transit surveys. Radial velocity surveys thus have a key role to play, in particular for giant planets. Cold Jupiters induce a typical radial velocity semi-amplitude of 10m.s^{-1}, which is well within the reach of multiple instruments that have now been in operation for more than a decade. Aims. We take advantage of the ongoing radial velocity survey with the sophie high-resolution spectrograph, which continues the search started by its predecessor elodie to further characterize the cold Jupiter population. Methods. Analyzing the radial velocity data from six bright solar-like stars taken over a period of up to 15 years, we attempt the detection and confirmation of Keplerian signals. Results. We announce the discovery of six planets, one per system, with minimum masses in the range 2.99-8.3 Mjup and orbital periods between 200 days and 10 years. The data do not provide enough evidence to support the presence of additional planets in any of these systems. The analysis of stellar activity indicators confirms the planetary nature of the detected signals. Conclusions. These six planets belong to the cold and massive Jupiter population, and four of them populate its eccentric tail. In this respect, HD 80869 b stands out as having one of the most eccentric orbits, with an eccentricity of 0.862^{+0.028}_{-0.018}. These planets can thus help to better constrain the migration and evolution processes at play in the gas giant population. Furthermore, recent works presenting the correlation between small planets and cold Jupiters indicate that these systems are good candidates to search for small inner planets.
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