55 research outputs found
A direct N-body integrator for modelling the chaotic, tidal dynamics of multibody extrasolar systems: TIDYMESS
Tidal dissipation plays an important role in the dynamical evolution of moons, planets, stars, and compact remnants. The interesting complexity originates from the interplay between the internal structure and external tidal forcing. Recent and upcoming observing missions of exoplanets and stars in the galaxy help to provide constraints on the physics of tidal dissipation. It is timely to develop new N-body codes, which allow for experimentation with various tidal models and numerical implementations. We present the open-source N-body code TIDYMESS, which stands for âTIdal DYnamics of Multibody ExtraSolar Systemsâ. This code implements a Creep deformation law for the bodies, parametrized by their fluid Love numbers and fluid relaxation times. Due to tidal and centrifugal deformations, we approximate the general shape of a body to be an ellipsoid. We calculate the associated gravitational field to quadruple order, from which we derive the gravitational accelerations and torques. The equations of motion for the orbits, spins and deformations are integrated directly using a fourth-order integration method based on a symplectic composition. We implement a novel integration method for the deformations, which allows for a time-step solely dependent on the orbits, and not on the spin periods or fluid relaxation times. This feature greatly speeds up the calculations, while also improving the consistency when comparing different tidal regimes. We demonstrate the capabilities and performance of TIDYMESS, particularly in the niche regime of parameter space where orbits are chaotic and tides become non-linear
Detectability of shape deformation in short-period exoplanets
Context
Short-period planets are influenced by the extreme tidal forces of their parent stars. These forces deform the planets causing them to attain nonspherical shapes. The nonspherical shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light-curves and the parameters derived for these planets.
Aims
We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We also aim to show how detecting planet deformation allows us to obtain an observational estimate of the second fluid Love number from the light curve, which provides valuable information about the internal structure of the planet.
Methods
We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. We used the modified ellc to generate the transit light curve for a deformed planet. Our model is parameterized by the Love number; therefore, for a given light curve we can derive the value of the Love number that best matches the observations.
Results
We simulated the known cases of WASP-103b and WASP-121b which are expected to be highly deformed. Our analyses show that instrumental precision â€50 ppm minâ1 is required to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in âŒ40 transits using the Hubble Space Telescope and in âŒ300 transits using the forthcoming CHEOPS instrument. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST will permit the detection of shape deformation with a single transit observation. However, the effects of instrumental and astrophysical noise must be considered as they can increase the number of transits required to reach the 50 ppm minâ1 detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the shape of the planet, thereby leading us to infer sphericity for a deformed planet. Accurate determination of the limb darkening coefficients is therefore required to confirm planet deformation
Planets in Mean-Motion Resonances and the System Around HD45364
In some planetary systems, the orbital periods of two of its members present
a commensurability, usually known by mean-motion resonance. These resonances
greatly enhance the mutual gravitational influence of the planets. As a
consequence, these systems present uncommon behaviors, and their motions need
to be studied with specific methods. Some features are unique and allow us a
better understanding and characterization of these systems. Moreover,
mean-motion resonances are a result of an early migration of the orbits in an
accretion disk, so it is possible to derive constraints on their formation.
Here we review the dynamics of a pair of resonant planets and explain how their
orbits evolve in time. We apply our results to the HD 45365 planetary system.Comment: invited review, 17 pages, 6 figure
Magnetic Fields in Earth-like Exoplanets and Implications for Habitability around M-dwarfs
We present estimations of dipolar magnetic moments for terrestrial exoplanets
using the Olson & Christiansen (2006) scaling law and assuming their interior
structure is similar to Earth. We find that the dipolar moment of fast rotating
planets (where the Coriolis force dominates convection in the core), may amount
up to ~80 times the magnetic moment of Earth, M_Earth, for at least part of the
planets' lifetime. For very slow rotating planets (where the force of inertia
dominates), the dipolar magnetic moment only reaches up to ~1.5 M_Earth.
Applying our calculations to currently confirmed rocky exoplanets, we find that
CoRoT-7b, Kepler-10b and 55 Cnc e can sustain dynamos up to ~ 18, 15 and 13
M_Earth, respectively. Our results also indicate that the magnetic moment of
rocky exoplanets not only depends on their rotation rate, but also on their
formation history, thermal state, age and composition, as well as the geometry
of the field. These results apply to all rocky planets, but have important
implications for the particular case of exoplanets in the Habitable Zone of
M-dwarfs.Comment: 4 pages, 1 figure, to appear in the Origins 2011 ISSOL & IAU Meeting
Conference Proceedings, Montpellier, France, July 3-8 201
A pre-Caloris synchronous rotation for Mercury
The planet Mercury is locked in a spin-orbit resonance where it rotates three
times about its spin axis for every two orbits about the Sun. The current
explanation for this unique state assumes that the initial rotation of this
planet was prograde and rapid, and that tidal torques decelerated the planetary
spin to this resonance. When core-mantle boundary friction is accounted for,
capture into the 3/2 resonance occurs with a 26% probability, but the most
probable outcome is capture into one of the higher-order resonances. Here we
show that if the initial rotation of Mercury were retrograde, this planet would
be captured into synchronous rotation with a 68% probability. Strong spatial
variations of the impact cratering rate would have existed at this time, and
these are shown to be consistent with the distribution of pre-Calorian impact
basins observed by Mariner 10 and MESSENGER. Escape from this highly stable
resonance is made possible by the momentum imparted by large basin-forming
impact events, and capture into the 3/2 resonance occurs subsequently under
favourable conditions.Comment: Nature Geosci., 201
An extrasolar planetary system with three Neptune-mass planets
Over the past two years, the search for low-mass extrasolar planets has led
to the detection of seven so-called 'hot Neptunes' or 'super-Earths' around
Sun-like stars. These planets have masses 5-20 times larger than the Earth and
are mainly found on close-in orbits with periods of 2-15 days. Here we report a
system of three Neptune-mass planets with periods of 8.67, 31.6 and 197 days,
orbiting the nearby star HD 69830. This star was already known to show an
infrared excess possibly caused by an asteroid belt within 1 AU (the Sun-Earth
distance). Simulations show that the system is in a dynamically stable
configuration. Theoretical calculations favour a mainly rocky composition for
both inner planets, while the outer planet probably has a significant gaseous
envelope surrounding its rocky/icy core; the outer planet orbits within the
habitable zone of this star.Comment: 17 pages, 3 figures, preprint of the paper published in Nature on May
18, 200
The magnetic field and multiple planets of the young dwarf AU~Mic
In this paper we present an analysis of near-infrared spectropolarimetric and
velocimetric data of the young M dwarf AU Mic, collected with SPIRou at the
Canada-France-Hawaii telescope from 2019 to 2022, mostly within the SPIRou
Legacy Survey. With these data, we study the large- and small-scale magnetic
field of AU Mic, detected through the unpolarized and circularly-polarized
Zeeman signatures of spectral lines. We find that both are modulated with the
stellar rotation period (4.86 d), and evolve on a timescale of months under
differential rotation and intrinsic variability. The small-scale field,
estimated from the broadening of spectral lines, reaches kG. The
large-scale field, inferred with Zeeman-Doppler imaging from Least-Squares
Deconvolved profiles of circularly-polarized and unpolarized spectral lines, is
mostly poloidal and axisymmetric, with an average intensity of G. We
also find that surface differential rotation, as derived from the large-scale
field, is 30% weaker than that of the Sun. We detect the radial
velocity (RV) signatures of transiting planets b and c, although dwarfed by
activity, and put an upper limit on that of candidate planet d, putatively
causing the transit-timing variations of b and c. We also report the detection
of the RV signature of a new candidate planet (e) orbiting further out with a
period of d, i.e., near the 4:1 resonance with b. The RV
signature of e is detected at 6.5 while those of b and c show up at
4, yielding masses of and
Earth masses for b and c, and a minimum mass of
Earth masses for e.Comment: MNRAS, in press (20 pages and 12 figures + 9 pages of supplementary
material
The effects of deformation inertia (kinetic energy) in the orbital and spin evolution of close-in bodies
The purpose of this work is to evaluate the effect of deformation inertia on tide dynamics, particularly within the context of the tide response equations proposed independently by BoueÌ et al. (Celest Mech Dyn Astron 126:31â60, 2016) and Ragazzo and Ruiz (Celest Mech Dyn Astron 128(1):19â59, 2017). The singular limit as the inertia tends to zero is analyzed, and equations for the small inertia regime are proposed. The analysis of Love numbers shows that, independently of the rheology, deformation inertia can be neglected if the tide-forcing frequency is much smaller than the frequency of small oscillations of an ideal body made of a perfect (inviscid) fluid with the same inertial and gravitational properties of the original body. Finally, numerical integration of the full set of equations, which couples tide, spin and orbit, is used to evaluate the effect of inertia on the overall motion. The results are consistent with those obtained from the Love number analysis. The conclusion is that, from the point of view of orbital evolution of celestial bodies, deformation inertia can be safely neglected. (Exceptions may occur when a higher-order harmonic of the tide forcing has a high amplitude.)publishe
Populations of planets in multiple star systems
Astronomers have discovered that both planets and binaries are abundant
throughout the Galaxy. In combination, we know of over 100 planets in binary
and higher-order multi-star systems, in both circumbinary and circumstellar
configurations. In this chapter we review these findings and some of their
implications for the formation of both stars and planets. Most of the planets
found have been circumstellar, where there is seemingly a ruinous influence of
the second star if sufficiently close (<50 AU). Hosts of hot Jupiters have been
a particularly popular target for binary star studies, showing an enhanced rate
of stellar multiplicity for moderately wide binaries (>100 AU). This was
thought to be a sign of Kozai-Lidov migration, however recent studies have
shown this mechanism to be too inefficient to account for the majority of hot
Jupiters. A couple of dozen circumbinary planets have been proposed around both
main sequence and evolved binaries. Around main sequence binaries there are
preliminary indications that the frequency of gas giants is as high as those
around single stars. There is however a conspicuous absence of circumbinary
planets around the tightest main sequence binaries with periods of just a few
days, suggesting a unique, more disruptive formation history of such close
stellar pairs.Comment: Invited review chapter, accepted for publication in "Handbook of
Exoplanets", ed. H. Deeg & J. A. Belmont
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