Jupiter-like Planets Research Articles

Architecture of Planetary Systems Predicted from Protoplanetary Disks Observed with ALMA. II. Evolution Outcomes and Dynamical Stability

Recent ALMA observations on disk substructures suggest the presence of embedded protoplanets in a large number of disks. The primordial configurations of these planetary systems can be deduced from the morphology of the disk substructure and serve as initial conditions for numerical investigation of their future evolution. Starting from the initial configurations of 12 multiplanetary systems deduced from ALMA disks, we carried out two-stage N-body simulation to investigate the evolution of the planetary systems at the disk stage, as well as the long-term orbital stability after the disk dispersal. At the disk stage, our simulation includes both the orbital migration and pebble/gas accretion effects. We found that a variety of planetary systems are produced and can be categorized into distant giant planets, Jupiter-like planets, Neptune-like planets, and distant small planets. We found that the disk-stage evolution and the final configurations are sensitive to both the initial mass assignments and viscosity. After the disk stage, we implement only mutual gravity between star and planets and introduce stochastic perturbative forces. All systems are integrated for up to 10 Gyr to test their orbital stability. Most planetary systems are found to be stable for at least 10 Gyr, with perturbative force in a reasonable range. Our result implies that a strong perturbation source such as stellar flybys is required to drive the planetary system unstable. We discuss the implications of our results on both the disk and planet observation, which may be confirmed by the next-generation telescopes such as JWST and ngVLA.

Eccentricity evolution in gaseous dynamical friction

ABSTRACT We analyse how drag forces modify the orbits of objects moving through extended gaseous distributions. We consider how hydrodynamic (surface area) drag forces and dynamical friction (gravitational) drag forces drive the evolution of orbital eccentricity. While hydrodynamic drag forces cause eccentric orbits to become more circular, dynamical friction drag can cause orbits to become more eccentric. We develop a semi-analytic model that accurately predicts these changes by comparing the total work and torque applied to the orbit at periapse and apoapse. We use a toy model of a radial power-law density profile, ρ ∝ r−γ, to determine that there is a critical γ = 3 power index, which separates the eccentricity evolution in dynamical friction: orbits become more eccentric for γ < 3 and circularize for γ > 3. We apply these findings to the infall of a Jupiter-like planet into the envelope of its host star. The hydrostatic envelopes of stars are defined by steep density gradients near the limb and shallower gradients in the interior. Under the influence of gaseous dynamical friction, an infalling object’s orbit will first decrease in eccentricity and then increase. The critical separation that delineates these regimes is predicted by the local density slope and is linearly dependent on polytropic index. More broadly, our findings indicate that binary systems may routinely emerge from common envelope phases with non-zero eccentricities that were excited by the dynamical friction forces that drove their orbital tightening.

Probing Planets with Exomoons: The Cases of Kepler-1708 b and Kepler-1625 b

Abstract The tidal interactions between a planet and moon can provide insight into the properties of the host planet. The recent exomoon candidates Kepler-1708 b-i and Kepler-1625 b-i are Neptune-sized satellites orbiting Jupiter-like planets and provide an opportunity to apply such methods. We show that if the tidal migration time is roughly equal to the age of these systems, then the tidal dissipation factor Q for the planets Kepler-1708 b and Kepler-1625 b have values of ∼3 × 105–3 × 106 and ∼1.5 × 105–4 × 105, respectively. In each case, these are consistent with estimates for gas-giant planets. Even though some work suggests an especially large semimajor axis for Kepler-1625 b-i, we find that this would imply a surprisingly low Q ∼ 2000 for a gas giant unless the moon formed at essentially its current position. More detailed predictions for the moons’ initial semimajor axis could provide even better constraints on Q, and we discuss the formation scenarios for a moon in this context. Similar arguments can be used as more exomoons are discovered in the future to constrain exoplanet interior properties. This could be especially useful for exoplanets near the sub-Neptune/super-Earth radius gap where the planet structure is uncertain.

Weak Seasonality on Temperate Exoplanets around Low-mass Stars

Abstract Planets with nonzero obliquity and/or orbital eccentricity experience seasonal variations of stellar irradiation at local latitudes. The extent of the atmospheric response can be crudely estimated by the ratio of the orbital timescale to the atmospheric radiative timescale. Given a set of atmospheric parameters, we show that this ratio depends mostly on the stellar properties and is independent of orbital distance and planetary equilibrium temperature. For Jupiter-like atmospheres, this ratio is ≪1 for planets around very low mass M dwarfs and ≳1 when the stellar mass is greater than about 0.6 solar mass. Complications can arise from various factors, including varying atmospheric metallicity, clouds, and atmospheric dynamics. Given the eccentricity and obliquity, the seasonal response is expected to be systematically weaker for gaseous exoplanets around low-mass stars and stronger for those around more massive stars. The amplitude and phase lag of atmospheric seasonal variations as a function of host stellar mass are quantified by idealized analytic models. At the infrared emission level in the photosphere, the relative amplitudes of thermal flux and temperature perturbations are negligible, and their phase lags are closed to −90° for Jupiter-like planets around very low mass stars. The relative amplitudes and phase lags increase gradually with increasing stellar mass. With a particular stellar mass, the relative amplitude and phase lag decrease from low- to high-infrared optical depth. We also present numerical calculations for a better illustration of the seasonal behaviors. Last, we discuss implications for the atmospheric circulation and future atmospheric characterization of exoplanets in systems with different stellar masses.

The Effect of Post-Newtonian Spin Precessions on the Evolution of Exomoons’ Obliquity

Abstract Putative natural massive satellites (exomoons) have gained increasing attention when they orbit Jupiter-like planets within the habitable zone of their host main-sequence star S. An exomoon s is expected to move within the equatorial plane of its host planet p, with its spin S s aligned with its orbital angular momentum L , which, in turn, is parallel to the planetary spin S p. If, in particular, the common tilt ε of such angular momenta to the plane of the satellite–planet motion about the star, assumed fixed, has certain values, the stellar latitudinal irradiation experienced on the exomoon may allow it to sustain life as we know it, at least for certain orbital configurations. An Earth analog (similar in mass, radius, oblateness, and obliquity) is considered, which orbits within 5–10 planetary radii R p from its Jupiter-like host planet. The de Sitter and Lense–Thirring spin precessions due to the general relativistic post-Newtonian (pN) field of the host planet have an impact on an exomoon’s habitability for a variety of different initial spin–orbit configurations. Here I show it by identifying long-term variations in the satellite’s obliquity ε s, where variations can be ≲10°–100°, depending on the initial spin–orbit configuration, with a timescale of ≃0.1–1 million years. Also the satellite’s quadrupole mass moment J 2 s induces obliquity variations that are faster than the pN ones but do not cancel them. Tidal dissipations, which may potentially have a relevant impact on the outlined pattern, are not included in the present analysis.

CORALIE radial velocity search for companions around evolved stars (CASCADES)

Context. The advent of asteroseismology as the golden path to precisely characterize single stars naturally led to synergies with the field of exoplanetology. Today, the precise determination of stellar masses, radii and ages for exoplanet-host stars is a driving force in the development of dedicated software and techniques to achieve this goal. However, as various approaches exist, it is clear that they all have advantages and inconveniences and that there is a trade-off between accuracy, efficiency, and robustness of the techniques. Aims. We aim to compare and discuss various modelling techniques for exoplanet-host red giant stars for which TESS data are available. The results of the seismic modelling are then used to study the dynamical evolution and atmospheric evaporation of the planetary systems. Methods. We study, in detail, the robustness, accuracy and precision of various seismic modelling techniques when applied to four exoplanet-host red giants observed by TESS. We discuss the use of global seismic indexes, the use of individual radial frequencies and that of non-radial oscillations. In each case, we discuss the advantages and inconveniences of the modelling technique. Results. We determine precise and accurate masses of exoplanet-host red giant stars orbited by long-period Jupiter-like planets using various modelling techniques. For each target, we also provide a model-independent estimate of the mass from a mean density inversion combined with radii values from Gaia and spectroscopic data. We show that no engulfment or migration is observed for these targets, even if their evolution is extended beyond their estimated seismic ages up the red giant branch.

Jupiter and jovian exoplanets in Palatini f(R¯) gravity

Some parts of the substellar evolution, such as fragmentation of a gaseous cloud and Jupiter-like planet's cooling, are demonstrated to be impacted by Palatini $f(\bar R)$ gravity. Using simple models describing those processes we show that the opacity mass limit as well as cooling time of jovian planets differ in modified gravity.

Probing Transit Timing Variations of three hot Jupiters: HATP-36b, HATP-56b, and WASP-52b

ABSTRACT We report the results of new transit observations for the three hot Jupiter-like planets, HATP-36b, HATP-56b, and WASP-52b, respectively. Transit timing variations (TTVs) are presented for these systems based on observations that span the period 2016–2020. The data were collected with the 0.6-m telescope at Adiyaman University (ADYU60, Turkey) and the 1.0 m telescope at TÜBİTAK National Observatory (TUG, Turkey). Global fits were performed to the combined light curves for each system along with the corresponding radial velocity (RV) data taken from the literature. The extracted parameters (for all three systems) are found to be consistent with the values from previous studies. Through fits to the combined mid-transit times data from our observations and the data available in the literature, an updated linear ephemeris is obtained for each system. Although a number of potential outliers are noted in the respective O-C diagrams, the majority of the data are consistent within the 3σ confidence level implying a lack of convincing evidence for the existence of additional objects in the systems studied.

Constraining the Orbit and Mass of epsilon Eridani b with Radial Velocities, Hipparcos IAD-Gaia DR2 Astrometry, and Multiepoch Vortex Coronagraphy Upper Limits

Abstract ϵ Eridani is a young planetary system hosting a complex multibelt debris disk and a confirmed Jupiter-like planet orbiting at 3.48 au from its host star. Its age and architecture are thus reminiscent of the early Solar System. The most recent study of Mawet et al., which combined radial-velocity data and Ms-band direct imaging upper limits, started to constrain the planet’s orbital parameters and mass, but are still affected by large error bars and degeneracies. Here we make use of the most recent data compilation from three different techniques to further refine ϵ Eridani b’s properties: RVs, absolute astrometry measurements from the Hipparcos and Gaia missions, and new Keck/NIRC2 Ms-band vortex coronagraph images. We combine this data in a Bayesian framework. We find a new mass, M b = 0.66 − 0.09 + 0.12 MJup, and inclination, i = 78 . 81 − 22.41 ° + 29.34 , with at least a factor 2 of improvement over previous uncertainties. We also report updated constraints on the longitude of the ascending node, the argument of the periastron, and the time of periastron passage. With these updated parameters, we can better predict the position of the planet at any past and future epoch, which can greatly help define the strategy and planning of future observations and with subsequent data analysis. In particular, these results can assist the search for a direct detection with JWST and the Nancy Grace Roman Space Telescope’s coronagraph instrument.

Charting nearby stellar systems: the intensity of Galactic cosmic rays for a sample of solar-type stars

ABSTRACT Cosmic rays can penetrate planetary atmospheres driving the formation of prebiotic molecules, which are important for the origin of life. We calculate the Galactic cosmic ray fluxes in the habitable zone (HZ) of five nearby, well-studied solar-type stars and at the orbits of two known exoplanets. We model the propagation of Galactic cosmic rays through the stellar winds using a combined 1.5D stellar wind and 1D cosmic ray transport model. We find that the HZ of 61 Cyg A has comparable Galactic cosmic ray fluxes to present-day Earth values. For the other four systems (ϵ Eri, ϵ Ind, ξ Boo B, and π1 UMa), the fluxes are orders of magnitude smaller than Earth values. Thus, it is unlikely that any as-of-yet undetected Earth-like planets in their HZs would receive a higher radiation dose than is received on Earth. $\epsilon \,$Ind b, a Jupiter-like planet orbiting at ∼11 au, receives higher Galactic cosmic ray fluxes than Earth. We find the suppression of Galactic cosmic rays is influenced by whether diffusion or advection dominates at GeV energies and at distances where the wind has reached its’ terminal velocity. For advectively dominated winds (∼younger systems), varying the astrospheric size influences the suppression significantly. For diffusion-dominated systems (∼older systems), the astrospheric size, and therefore knowledge of the interstellar medium properties, are not very important. This reduces the Galactic cosmic ray flux uncertainties in the HZ for diffusion-dominated systems. Whether a system is advection- or diffusion-dominated can be determined from the stellar wind properties.

Optimized modelling of Gaia–Hipparcos astrometry for the detection of the smallest cold Jupiter and confirmation of seven low-mass companions

ABSTRACT To fully constrain the orbits of low-mass circumstellar companions, we conduct combined analyses of the radial velocity data and the Gaia and Hipparcos astrometric data for eight nearby systems. Our study shows that companion-induced position and proper motion differences between Gaia and Hipparcos are significant enough to constrain orbits of low-mass companions to a precision comparable with previous combined analyses of direct imaging and radial velocity data. We find that our method is robust to whether we use Gaia Data Release 2 or Gaia Early Data Release 3, as well as whether we use all of the data or just proper motion differences. In particular, we fully characterize the orbits of HD 190360 b and HD 16160 C for the first time. With a mass of 1.8 ± 0.2 MJup and an effective temperature of 123–176 K and orbiting around a Sun-like star, HD 190360 b is the smallest Jupiter-like planet with well-constrained mass and orbit, belonging to a small sample of fully characterized Jupiter analogues. It is separated from its primary star by 0.25 arcsec and thus may be suitable for direct imaging by the coronagraph instrument of the Roman Space Telescope.

The future of Jupiter-like planets around Sun-like stars: first steps

AbstractPlanets that orbit low- to intermediate mass main sequence (MS) stars will experience vigorous star-planet interactions when the host star evolves through the giant branches, including the asymptotic giant branch (AGB) phase, due to extreme luminosities and stellar outflows. In this work, we take the first steps towards understanding how a planet’s temperature profile and chemical composition is altered when the host star evolves from the MS to the AGB phase. We used a 1D radiative transfer code to compute the temperature-pressure profile and a 1D chemical kinetics code to simulate the disequilibrium chemistry. We consider a Jupiter-like planet around a Solar-type star in two evolutionary stages (MS and AGB planet) by only varying the stellar luminosity. We find that the temperature throughout the AGB planet’s atmosphere is increased by several hundreds of Kelvin compared to the MS planet. We also find that CO joins H2O and CH4 as a prominent constituent in the AGB planet’s atmospheric composition.

AnN-body population synthesis framework for the formation of moons around Jupiter-like planets

ABSTRACTThe moons of giant planets are believed to form in situ in circumplanetary discs (CPDs). Here, we present an N-body population synthesis framework for satellite formation around a Jupiter-like planet, in which the dust-to-gas ratio, the accretion rate of solids from the protoplanetary disc, the number, and the initial positions of protosatellites were randomly chosen from realistic distributions. The disc properties were from 3D radiative simulations sampled in 1D and 2D grids and evolved semi-analytically with time. The N-body satellitesimals accreted mass from the solid component of the disc, interacted gravitationally with each other, experienced close-encounters, both scattering and colliding. With this improved modeling, we found that only about $15{{\ \rm per\ cent}}$ of the resulting population is more massive than the Galilean one, causing migration rates to be low and resonant captures to be uncommon. In 10 per cent of the cases, moons are engulfed by the planet, and 1 per cent of the satellite-systems lose at least 1 Earth-mass into the planet, contributing only in a minor part to the giant planet’s envelope’s heavy element content. We examined the differences in outcome between the 1D and 2D disc models and used machine learning techniques (Randomized Dependence Coefficient together with t-SNE) to compare our population with the Galilean system. Detecting our population around known transiting Jupiter-like planets via transits and TTVs would be challenging, but $14{{\ \rm per\ cent}}$ of the moons could be spotted with an instrumental transit sensitivity of 10−5.

Hard X-Ray Emission Associated with White Dwarfs. IV. Signs of Accretion from Substellar Companions

Abstract With an effective temperature of ≃200,000 K, KPD 0005+5106 is one of the hottest white dwarfs (WDs). ROSAT unexpectedly detected “hard” (∼1 keV) X-rays from this apparently single WD. We have obtained Chandra observations that confirm the spatial coincidence of this hard X-ray source with KPD 0005+5106. We have also obtained XMM-Newton observations of KPD 0005+5106, as well as PG 1159−035 and WD 0121−756, which are also apparently single and whose hard X-rays were detected by ROSAT at 3σ–4σ levels. The XMM-Newton spectra of the three WDs show remarkably similar shapes that can be fitted by models including a blackbody component for the stellar photospheric emission, a thermal plasma emission component, and a power-law component. Their X-ray luminosities in the 0.6–3.0 keV band range from 4 × 1029 to 4 × 1030 erg s−1. The XMM-Newton EPIC-pn soft-band (0.3–0.5 keV) light curve of KPD 0005+5106 is essentially constant, but the hard-band (0.6–3.0 keV) light curve shows periodic variations. An analysis of the generalized Lomb–Scargle periodograms for the XMM-Newton and Chandra hard-band light curves finds a convincing modulation (false-alarm probability of 0.41%) with a period of 4.7 ± 0.3 hr. Assuming that this period corresponds to a binary orbital period, the Roche radii of three viable types of companion have been calculated: M9V star, T brown dwarf, and Jupiter-like planet. Only the planet has a size larger than its Roche radius, although the M9V star and T brown dwarf may be heated by the WD and inflate past the Roche radius. Thus, all three types of companion may be donors to fuel accretion-powered hard X-ray emission.

Giant planet scatterings and collisions: hydrodynamics, merger-ejection branching ratio, and properties of the remnants

ABSTRACT Planetary systems with sufficiently small orbital spacings can experience planetary mergers and ejections. The branching ratio of mergers versus ejections depends sensitively on the treatment of planetary close encounters. Previous works have adopted a simple ‘sticky-sphere’ prescription, whose validity is questionable. We apply both smoothed particle hydrodynamics and N-body integrations to investigate the fluid effects in close encounters between gas giants and the long-term evolution of closely packed planetary systems. Focusing on parabolic encounters between Jupiter-like planets with MJ and 2MJ, we find that quick mergers occur when the impact parameter rp (the pericentre separation between the planets) is less than 2RJ, and the merger conserved at least 97 per cent of the initial mass. Strong tidal effects can affect the ‘binary-planet’ orbit when rp is between 2RJ and 4RJ. We quantify these effects using a set of fitting formulae that can be implemented in N-body codes. We run a suite of N-body simulations with and without the formulae for systems of two giant planets initially in unstable, nearly circular and coplanar orbits. The fluid (tidal) effects significantly increase the branching ratio of planetary mergers relative to ejections by doubling the effective collision radius. While the fluid effects do not change the distributions of semimajor axis and eccentricity of each type of remnant planets (mergers versus surviving planets in ejections), the overall orbital properties of planet scattering remnants are strongly affected due to the branching ratio change. We also find that the merger products have broad distributions of spin magnitudes and obliquities.

51 Pegasi b: The planet that started the revolution of exoplanet research

To celebrate its 150 anniversary, Nature collected 10 extraordinary papers published on Nature in November, 2019. One of the papers is on the discovery of the 51 Peg b by Swiss astronomers Michel Mayor and Didier Queloz from University of Geneva. 51 Peg b was the first confirmed planet around a solar-type star other than our own Sun. Mayor and Queloz later won the Nobel Physics Prize in 2019 because they have “explored our cosmic neighbourhoods on the hunt for unknown planets. Their discoveries have forever changed our conceptions of the world.” The discovery was made using the radial velocity technique. A star and a planet orbit each other, and although not much, the star still shows a noticeable wobble due to the gravitational tug of the planet. By observing this wobble motion, scientists can infer the existence of a planet around the star and calculate its mass and distance from the host star. Mayor and Queloz started their planet survey using ELODIE spectrograph in the early 1990s at Haute-Provence Observatory. Through their survey, they found a strange object orbiting the star 51 Pegasi, with a similar mass of Jupiter, but about 7 times closer to its host star than Mercury is to our sun. This object was later named as 51 Pegasi b, and confirmed by other research teams around the world, including Marcy’s research team from America. This new discovery was a big challenge to the traditional models of planet formation. How could a Jupiter-like planet form so close to its host star? Revised planet formation theory suggests 51 Peg b initially formed like a Jupiter farther away from 51 Pegasi, and later migrated inwards towards the star due to interaction with other planets or interaction with the material in the gaseous planetary disk. Since the discovery of 51 Peg b, more than 4200 exoplanets have been confirmed so far, and many more yet coming. The main detection methods of exoplanets are radial velocity technique, transiting technique, microlensing, and direct imaging methods. Most of the planets known today are detected using radial velocity technique and transiting technique. A lot of these planet systems are quite different from our Solar system, which makes people wondering, is our Solar system unique in the Universe? As more and more planets are detected, astronomers keep revising the theory of planet formation to account for the new discoveries. Eventually we will figure out the position of our own solar system in the Univerise, and how planets form. In the present paper, we will first briefly review the discovery of the first confirmed exoplanet around a solar-type star, 51 Peg b by Mayor and Queloz in 1995. Then, we introduce the properties of this extraordinary planet system, and show how this planet system single handly changed our view of planet formation. We shall also introduce the impact of this discovery on the exoplanet community and astronomy community as a whole. In the end, we point out the important implications of the discovery of 51 Peg b.

Detecting Exoplanets Using Eclipsing Binaries as Natural Starshades

Abstract We investigate directly imaging exoplanets around eclipsing binaries using the eclipse as a natural tool for dimming the binary and thus increasing the planet to star brightness contrast. At eclipse, the binary becomes pointlike, making coronagraphy possible. We select binaries where the planet–star contrast would be boosted by >10× during eclipse, making it possible to detect a planet that is ≳10× fainter or in a star system that is ∼2–3× more massive than otherwise. Our approach will yield insights into planet occurrence rates around binaries versus individual stars. We consider both self-luminous (SL) and reflected light (RL) planets. In the SL case, we select binaries whose age is young enough so that an orbiting SL planet would remain luminous; in U Cep and AC Sct, respectively, our method is sensitive to SL planets of ∼4.5 and ∼9 M J with current ground- or near-future space-based instruments and ∼1.5 and ∼6 M J with future ground-based observatories. In the RL case, there are three nearby (≲50 pc) systems—V1412 Aql, RR Cae, and RT Pic—around which a Jupiter-like planet at a planet–star separation of ≳20 mas might be imaged with future ground- and space-based coronagraphs. A Venus-like planet at the same distance might be detectable around RR Cae and RT Pic. A habitable Earth-like planet represents a challenge; while the planet–star contrast at eclipse and planet flux are accessible with a 6–8 m space telescope, the planet–star separation is 1/3–1/4 of the angular separation limit of modern coronagraphy.

Eclipse timing variation of GK Vir: evidence of a possible Jupiter-like planet in a circumbinary orbit

ABSTRACT Eclipse timing variation analysis has become a powerful method to discover planets around binary systems. We applied this technique to investigate the eclipse times of GK Vir. This system is a post-common envelope binary with an orbital period of 8.26 h. Here, we present 10 new eclipse times obtained between 2013 and 2020. We calculated the O−C diagram using a linear ephemeris and verified a clear orbital period variation (OPV) with a cyclic behaviour. We investigated if this variation could be explained by the Applegate mechanism, the apsidal motion, or the light travel time (LTT) effect. We found that the Applegate mechanism would hardly explain the OPV with its current theoretical description. We obtained using different approaches that the apsidal motion is a less likely explanation than the LTT effect. We showed that the LTT effect with one circumbinary body is the most likely cause for the OPV, which was reinforced by the orbital stability of the third body. The LTT best solution provided an orbital period of ∼24 yr for the outer body. Under the assumption of coplanarity between the external body and the inner binary, we obtained a Jupiter-like planet around the GK Vir. In this scenario, the planet has one of the longest orbital periods, with a full observational baseline, discovered so far. However, as the observational baseline of GK Vir is smaller than twice the period found in the O−C diagram, the LTT solution must be taken as preliminary.

Acoustic and inertial modes in planetary-like rotating ellipsoids.

The bounded oscillations of rotating fluid-filled ellipsoids can provide physical insight into the flow dynamics of deformed planetary interiors. The inertial modes, sustained by the Coriolis force, are ubiquitous in rapidly rotating fluids and Vantieghem (2014, Proc. R. Soc. A, 470, 20140093. doi:10.1098/rspa.2014.0093) pioneered a method to compute them in incompressible fluid ellipsoids. Yet, taking density (and pressure) variations into account is required for accurate planetary applications, which has hitherto been largely overlooked in ellipsoidal models. To go beyond the incompressible theory, we present a Galerkin method in rigid coreless ellipsoids, based on a global polynomial description. We apply the method to investigate the normal modes of fully compressible, rotating and diffusionless fluids. We consider an idealized model, which fairly reproduces the density variations in the Earth's liquid core and Jupiter-like gaseous planets. We successfully benchmark the results against standard finite-element computations. Notably, we find that the quasi-geostrophic inertial modes can be significantly modified by compressibility, even in moderately compressible interiors. Finally, we discuss the use of the normal modes to build reduced dynamical models of planetary flows.

Giant Planet Swaps during Close Stellar Encounters

Abstract The discovery of planetary systems outside of the solar system has challenged some of the tenets of planetary formation. Among the difficult-to-explain observations are systems with a giant planet orbiting a very low mass star, such as the recently discovered GJ 3512b planetary system, where a Jupiter-like planet orbits an M star in a tight and eccentric orbit. Systems such as this one are not predicted by the core accretion theory of planet formation. Here we suggest a novel mechanism, in which the giant planet is born around a more typical Sun-like star ( ), but is subsequently exchanged during a dynamical interaction with a flyby low-mass star ( ). We perform state-of-the-art N-body simulations with and to study the statistical outcomes of this interaction, and show that exchanges result in high eccentricities for the new orbit around the low-mass star, while about half of the outcomes result in tighter orbits than the planet had around its birth star. We numerically compute the cross section for planet exchange, and show that an upper limit for the probability per planetary system to have undergone such an event is Gyr−1, where a p is the planet semimajor axis around the birth star, σ the velocity dispersion of the star cluster, and M c the total mass of the star cluster. Hence these planet exchanges could be relatively common for stars born in open clusters and groups, should already be observed in the exoplanet database, and provide new avenues to create unexpected planetary architectures.