Context. The dynamics of solar system objects, such as dwarf planets and asteroids, has become a well-established field of celestial mechanics in the past thirty years, owing to the improvements that ...have been made in observational techniques and numerical studies. In general, the ecliptic is taken as the reference plane in these studies, although there is no dynamical reason for doing so. In contrast, the invariable plane as originally defined by Laplace, seems to be a far more natural choice. In this context, the latest study of this plane dates back to Burkhardt. Aims. We define and determine the orientation of the invariable plane of the solar system with respect to both the ICRF and the equinox-ecliptic of J2000.0, and evaluate the accuracy of our determination. Methods. Using the long-term numerical ephemerides DE405, DE406, and INPOP10a over their entire available time span, we computed the total angular momentum of the solar system, as well as the individual contribution to it made by each of the planets, the dwarf planets Pluto and Ceres, and the two asteroids Pallas and Vesta. We then deduced the orientation of the invariable plane from these ephemerides. Results. We update the previous results on the determination of the orientation of the invariable plane with more accurate data, and a more complete analysis of the problem, taking into account the effect of the dwarf planet (1) Ceres as well as two of the biggest asteroids, (4) Vesta and (2) Pallas. We show that the inclusion of these last three bodies significantly improves the accuracy of determination of the invariable plane, whose orientation over a 100 y interval does not vary more than 0.1 mas in inclination, and 0.3 mas in longitude of the ascending node. Moreover, we determine the individual contributions of each body to the total angular momentum of the solar system, as well as the inclination and longitude of the node with respect to this latter plane. Conclusions. Owing to the high accuracy of its determination and its fundamental dynamical meaning, the invariable plane provides a permanent natural reference plane that should be used when studying solar system dynamics, instead of the ecliptic. Since it is fixed in an isolated solar system, whereas the ecliptic alters with time, we recommend referring to it when working on long-term dynamics.
ABSTRACT
We revisit the concept of spheres of gravitational activity, to which we give both a geometrical and a physical meaning. This study aims to refine this concept in a much broader context that ...could, for instance, be applied to exo-planetary problems (in a Galactic stellar disc–star–planets system) in order to define a first-order ‘boundary’ of a planetary system. The methods used in this paper rely on classical Celestial Mechanics and develop the equations of motion in the framework of the three-body problem (e.g. Star-Planet-Satellite System). We start with the basic definition of a planet’s sphere of activity as the region of space in which it is feasible to assume the planet as the central body and the Sun as the perturbing body when computing perturbations of the satellite’s motion. We then investigate the geometrical properties and physical meaning of the ratios of solar accelerations (central and perturbing) and planetary accelerations (central and perturbing), and the boundaries they define. Throughout the paper, we clearly distinguish amongst the sphere of activity, the Chebotarev sphere (a particular case of the sphere of activity), the Laplace sphere, and the Hill sphere. The last two are often wrongfully thought to be one and the same. Furthermore, by taking a closer look at and comparing the ratio of the star’s accelerations (central/perturbing) with that of the planetary accelerations (central/perturbing) as a function of the planeto-centric distance, we have identified different dynamical regimes, which are presented in the semi-analytical analysis.
Context.
Neptune’s incomplete ring arcs have been stable since their discovery in 1984 by stellar occultation. Although these structures should be destroyed within a few months through differential ...Keplerian motion, imaging data over the past couple of decades have shown that these structures remain stable.
Aims.
We present the first SPHERE near-infrared observations of Neptune’s ring arcs taken at 2.2 μm (broadband
Ks
) with the IRDIS camera at the Very Large Telescope (VLT) in August 2016.
Methods.
The images were aligned using the ephemerides of the satellite Proteus and were suitably co-added to enhance ring and satellite signals.
Results.
We analyse high-angular-resolution near-infrared images of Neptune’s ring arcs obtained in 2016 at the ESO VLT-UT3 with the adaptive-optics-fed camera SPHERE-IRDIS. We derive accurate mean motion values for the arcs and the nearby satellite Galatea. The trailing arcs Fraternité and Égalité have been stable since they were last observed in 2007. Furthermore, we confirm the fading away of the leading arcs Courage and Liberté. Finally, we confirm the mismatch between the arcs’ position and the 42:43 inclined and eccentric corotation resonances with Galatea, thus demonstrating that no 42:43 corotation model works to explain the azimuthal confinement of the arcs’ materiel.
ABSTRACT
Recording a stellar occultation is one powerful method that gives direct information about the physical properties of the occulting Solar system object. In order to obtain reliable and ...accurate results, simultaneous observations from different locations across-track of the projected path are of great importance. However, organizing all the observing stations, aggregating, and analysing the data is time-consuming and not that easy. We have developed a web portal named Occultation Portal (OP) to manage all those occultation observation campaigns from a central server. With this portal, the instrumental and observational information of all observers participating in a stellar occultation campaign and the concerned data are archived systematically in a standard format. The researchers can then visualize the archived data on an event basis. The investigators can also extract the light curve for each data set with the added reduction pipeline to the portal base. This paper describes in detail the portal structure and the developed features.
Astrometry covers a parameter space that cannot be reached by RV or transit methods to detect terrestrial planets on wide orbits. In addition, high accuracy astrometric measurements are necessary to ...measure the inclination of the planet's orbits. Here we investigate the principles of an artefact of the astrometric approach, namely the displacement of the photo-centre owing to inhomogeneities in a dust disc around the parent star. Indeed, theory and observations show that circumstellar discs can present strong asymmetries. We model the pseudo-astrometric signal caused by these inhomogeneities, asking whether a dust clump in a disc can mimic the astrometric signal of an Earth-like planet. We show that these inhomogeneities cannot be neglected when using astrometry to find terrestrial planets. We provide the parameter space for which these inhomogeneities can affect the astrometric signals but still not be detected by mid-IR observations. We find that a small cross section of dust corresponding to a cometary mass object is enough to mimic the astrometric signal of an Earth-like planet. Astrometric observations of protoplanetary discs to search for planets can also be affected by the presence of inhomogeneities. Some further tests are given to confirm whether an observation is a real astrometric signal from a planet or an impostor. Eventually, we also study the case where the cross-section of dust is high enough to provide a detectable IR-excess and to have a measurable photometric displacement by actual instruments such as Gaia, IRAC, or GRAVITY. We suggest a new method, which consists of using astrometry to quantify asymmetries (clumpiness) in inner debris discs that cannot be otherwise resolved.
The asteroid (31) Euphrosyne is the largest body of its namesake family, and it contains more than 99% of the family mass. Among large asteroid families, the Euphrosyne group is peculiar because of ...its quite steep size-frequency distribution (SFD), significantly depleted in large- and medium-sized asteroids (8 < D < 12 km). The current steep SFD of the Euphrosyne family has been suggested to be the result of a grazing impact in which only the farthest, smallest members failed to accrete. The Euphrosyne family is, however, also very peculiar because of its dynamics: near its center it is crossed by the nu sub(6) = g - g sub(6) linear secular resonance, and it hosts the largest population (140 bodies) of asteroids in nu sub(6) antialigned librating states (or Tina-like asteroids) in the main belt. In this work we investigated the orbital evolution of newly obtained members of the dynamical family, with an emphasis on its interaction with the nu sub(6) resonance. Because of its unique resonant configuration, large- and medium-sized asteroids tend to migrate away from the family orbital region faster than small-sized objects, which were ejected farther away from the family center. As a consequence, the SFD of the Euphrosyne family becomes steeper in time with a growing depletion in the number of the largest family members. We estimate that the current SFD could be attained from a typical, initial SFD on timescales of 500 Myr, consistent with estimates of the family age obtained with other independent methods.
It has been shown that large families are not limited to what found by hierarchical clustering methods in the domain of proper elements (a, e, sin (i)), which seems to be biased to find compact, ...relatively young clusters, but that there exists an extended population of objects with similar taxonomy and geometric albedo, which can extend to much larger regions in proper elements and frequencies domains: the family 'halo'. Numerical simulations can be used to provide estimates of the age of the family halo, which can then be compared with ages of the family obtained with other methods. Determining a good estimate of the possible orbital extension of a family halo is therefore quite important, if one is interested in determining its age and, possibly, the original ejection velocity field. Previous works have identified families' haloes by an analysis in proper elements domains, or by using Sloan Digital Sky Survey-Moving Object Catalog data, fourth release (SDSS-MOC4) multiband photometry to infer the asteroid taxonomy, or by a combination of the two methods. The limited number of asteroids for which geometric albedo was known until recently discouraged in the past the extensive use of this additional parameter, which is however of great importance in identifying an asteroid taxonomy. The new availability of geometric albedo data from the Wide-field Infrared Survey Explorer (WISE) mission for about 100 000 asteroids significantly increased the sample of objects for which such information, with some errors, is now known.
In this work, we proposed a new method to identify families' haloes in a multidomain space composed by proper elements, SDSS-MOC4 (a*, i − z) colours, and WISE geometric albedo for the whole main belt (and the Hungaria and Cybele orbital regions). Assuming that most families were created by the breakup of an undifferentiated parent body, they are expected to be homogeneous in colours and albedo. The new method is quite effective in determining objects belonging to a family halo, with low percentages of likely interlopers, and results that are quite consistent in term of taxonomy and geometric albedo of the halo members.
Context. Neptune’s incomplete ring arcs have been stable since their discovery in 1984 although these structures should be destroyed in a few months through differential Keplerian motion. Regular ...imaging data are needed to address the question of the arc stability. Aims. We present the first NACO observations of Neptune’s ring arcs taken at 2.2 μm (Ks band) with the Very Large Telescope in August 2007, and propose a model for the arc stability based on co-orbital motion. Methods. The images were aligned using the ephemerides of the satellites Proteus and Triton and were suitably co-added to enhance ring or satellite signals. Resonance theory and N-body simulations were used to model the arcs’ confinement. Results. We derive accurate mean motion values for the arcs and Galatea and confirm the mismatch between the arcs’ position and the location of the 42:43 corotation inclination resonance. We propose a new confinement mechanism where small co-orbital satellites in equilibrium trap ring arc material. We constrain the masses and locations of these hypothetical co-orbital bodies.
We were able to accurately predict the shadow path and successfully observe an occultation of a bright star by Chiron on December 15, 2022. The Kottamia Astronomical Observatory in Egypt did not ...detect the occultation by the solid body, but we found three extinction features in the light curve that had symmetrical counterparts with respect to the central time of the occultation. One of the features is broad and shallow, whereas the other two features are sharper, with a maximum extinction of ∼25% at the achieved spatial resolution of 19 km per data point. From the Wise Observatory in Israel, we detected the occultation caused by the main body and several extinction features surrounding the body. When all the secondary features are plotted in the sky plane, we find that they can be caused by a broad ∼580 km disk with concentrations at radii of 325 ± 16 km and 423 ± 11 km surrounding Chiron. At least one of these structures appears to be outside the Roche limit. The ecliptic coordinates of the pole of the disk are
λ
= 151° ±8° and
β
= 18° ±11°, in agreement with previous results. We also reveal our long-term photometry results, indicating that Chiron had suffered a brightness outburst of at least 0.6 mag between March and September 2021 and that Chiron was still somewhat brighter at the occultation date than at its nominal pre-outburst phase. The outermost extinction features might be consistent with a bound or temporarily bound structure associated with the brightness increase. However, the nature of the brightness outburst is unclear, and it is also unclear whether the dust or ice released in the outburst could be feeding a putative ring structure or whether it is emanating from it.
The asteroid (10) Hygiea is the fourth largest asteroid of the main belt, by volume and mass, and it is the largest member of its own family. Previous works investigated the long-term effects of ...close encounters with (10) Hygiea of asteroids in the orbital region of the family, and analysed the taxonomical and dynamical properties of members of this family. In this paper we apply the high-quality Sloan Digital Sky Survey-Moving Object Catalog data, fourth release (SDSS-MOC4) taxonomic scheme of DeMeo & Carry to members of the Hygiea family core and halo, we obtain an estimate of the minimum time and number of encounter necessary to obtain a 3σ (or 99.7 per cent) compatible frequency distribution function of changes in proper a caused by close encounters with (10) Hygiea, we study the behaviour of asteroids near secular resonance configurations, in the presence and absence of the Yarkovsky force, and obtain a first estimate of the age of the family based on orbital diffusion by the Yarkovsky and Yarkovsky-O'Keefe-Radzievsky-Paddack (YORP) effects with two methods.
The Hygiea family is at least 2 Byr old, with an estimated age of
Myr and a relatively large initial ejection velocity field, according to the approach of Vokrouhlický et al. Surprisingly, we found that the family age can be shortened by 25 per cent if the dynamical mobility caused by close encounters with (10) Hygiea is also accounted for, which opens interesting new research lines for the dynamical evolution of families associated with massive bodies. In our taxonomical analysis of the Hygiea asteroid family, we also identified a new V-type candidate: the asteroid (177904) (2005 SV5). If confirmed, this could be the fourth V-type object ever to be identified in the outer main belt.
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