Natural Planetary Satellites Research Articles

GaiaData Release 3

Context.The third data release by theGaiamission of the European Space Agency (DR3) is the first release to provide the community with a large sample of observations for more than 150 thousand Solar System objects, including asteroids and natural planetary satellites. The release contains astrometry (over 23 million epochs) and photometry, along with average reflectance spectra of 60518 asteroids and osculating elements.Aims.We present an overview of the procedures that have been implemented over several years of development and tests to process Solar System data at the level of accuracy thatGaiacan reach. We illustrate the data properties and potential with some practical examples.Methods.In order to allow the users ofGaiaDR3 to best exploit the data, we explain the assumptions and approaches followed in the implementation of the data processing pipeline for Solar System processing, and their effects in terms of data filtering, optimisation, and performances. We then test the data quality by analysing post-fit residuals to adjusted orbits, the capacity of detecting subtle dynamical effects (wobbling due to satellites or shape and Yarkovsky acceleration), and to reproduce known properties of asteroid photometry (phase curves and rotational light curves).Results.The DR3 astrometric accuracy is a clear improvement over the data published in DR2, which concerned a very limited sample of asteroids. The performance of the data reduction is met, and is illustrated by the capacity of detecting milliarcsecond-level wobbling of the asteroid photocentre that is due to satellite or shape effects and contributes to Yarkovsky effect measurements.Conclusions.The third data release can in terms of data completeness and accuracy be considered the first full-scale realisation of the Solar System survey byGaia.

Astrometric Results for Observations of Jupiter’s Galilean Satellites During Mutual Occultations and Eclipses in 2009 and 2014–2015

Photometric observations of satellites during their mutual occultations and eclipses are a valuable source of astrometric data for studying the motion of natural planetary satellites. Worldwide photometric observation campaigns are organized in order to observe as many phenomena as possible. All the photometric results obtained during such an observation campaign are stored in a single database, and after some time, they undergo astrometric processing. After conducting the campaign and publishing the results, some observers find unused data, which appear valuable. We have collected these photometric observations of mutual occultations and eclipses of Jupiter’s Galilean satellites and processed them to utilize these valuable astrometric data. To obtain astrometric data from the photometric observations, we have applied our original method. The observations come from eight observatories worldwide. As a result, this work presents 32 new relative astrometric positions of Jupiter’s Galilean satellites in 2009 and 23 new positions in 2014–2015. The astrometric accuracy of the new data in comparison with the most developed theory (O–C) is approximately 0.05′′. The internal accuracy, based on estimates for random photometry errors, is 0.02′′.

Natural satellites mutual phenomena observations: Achievements and future

Astrometry of Solar system objects needs to perform observations regularly since the motions are fast and the dynamical models need sample of data on long intervals of time.The goal of this paper is to show that some phenomena occurring during the equinox on the giant planets are worth to be observed. Past experience has shown the interest of such observations which should be continued in the future due to their relevant contribution to improve the dynamical models.Using the best ephemerides of the natural planetary satellites, we calculate the next phenomena to occur in order to prepare the future observational campaigns.We provide in this paper the tables of the dates of the next phenomena as their observational conditions which depends on the opposition and the declination of the planet.Past observations provided particularly accurate data, better than all the other ground based observations and we encourage observations in the next future especially for planetary systems for which no space mission is planned.

The astrometry of the natural planetary satellites applied to their dynamics before and after Gaia

The natural planetary satellites are observed since centuries in order to understand their dynamics and their evolution. A high level astrometric accuracy is necessary for this purpose. The arrival of Gaia makes necessary to perform the ground-based observations in the scope of the future data provided by Gaia. About 50 observations by Gaia of each satellite will be available, and the Gaia star catalogue will allow to reduce the astrometric observations with a high level accuracy. This is true for observations made at the present time, made in the future, and made in the past thanks to a new reduction of old observations such as photographic plates. We analyse the different status of the satellites depending on the system of which they belong. This will decide the astrometric observing programmes of the natural planetary satellites for the next years.

Astrometric results of observations of mutual occultations and eclipses of the Saturnian satellites in 2009

Context. The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events. Aims. This work focuses on processing the complete database of photometric observations of the mutual occultations and eclipses of the Uranian satellites made during the international campaign in 2007. The final goal is to derive new accurate astrometric data. Methods. We used an accurate photometric model of mutual events that explicitly depends on parameters that these accurate observations should be sensitive to, including the albedos of the satellites. Our original method is applied to derive astrometric data in relative positions from photometric observations of mutual occultations and eclipses of the Uranian satellites. Results. We process the 41 light-curves obtained during the international campaign of photometric observations of the Uranian satellites in 2007. The root-mean-square (rms) of the residuals “observations minus calculations” (O‐C) with respect to theory for the best 34 observations are equal to 10.3 and 17.7 mas in right ascension and declination, respectively. For five observations only the position angle was derived. Topocentric or heliocentric angular differences for satellites pairs were obtained from 25 central instant offsets between observation and theory during the time period from May 4, 2007 to January 4, 2008. Conclusions. The rms of the residuals is from 10 to 20 mas that corresponds in situ to 10 to 20 km. These mutual event observations appear to be the most accurate astrometric ground-based observations of the major Uranian satellites to-date and should be used for dynamical purposes.

Estimates of the physical parameters of remote planetary satellites

Since 1998, 97 new remote satellites of Jupiter, Saturn, Uranus, and Neptune have been discovered. Since their brightness is rather weak, it is difficult to perform their photometry and determine their physical parameters. For 27 satellites from this group, different authors carried out special photometric investigations. For the other 70 satellites, the magnitudes accompanying the results of astrometric observations published in Minor Planet Circulars (MPC) are the only photometric data. In the present study, the photometric model parameters for all of the 97 remote satellites have been determined. From the hypothetic values of albedo and material density of the satellites, their sizes and gravitation parameters have been estimated. The whole volume of the obtained results is available in the database of the natural planetary satellites (NSDB) (Arlot and Emelyanov, 2009) published on the Internet ( http://www.sai.msu.ru/neb/nss/index.htm ).

A new astrometric reduction of photographic plates using the DAMIAN digitizer: improving the dynamics of the Jovian system

Abstract : The astrometric monitoring of the natural planetary satellites is an important step to assess the formation and the evolution of these systems. However, in order to quantify relevant gravitational effects such as tidal forces, it is necessary to have very accurate observations over a long time interval. Unfortunately, the accuracy is decreasing as one considers older observations. To solve this issue, digitizing of old photographic plates is an attractive method, but a high accuracy in the measurement and the reduction of those plates is absolutely necessary. We have developed methods and algorithms adapted to specific plates provided by USNO, using the DAMIAN digitizer of ROB. From a set of 35 plates taken in 1974, we have been able to produce measurements with an accuracy better than 0.08 micrometers and after reduction using the UCAC2 catalogue, rms residuals of 35 mas (1.7 micrometers) for intersatellite positions (when the original reduction provided 100 mas) and of 65 mas for equatorial RA and Dec. positions (which were not possible to get with the original reduction). First results on the dynamics of the satellites and of the planet Jupiter are provided.

Frozen orbits at high eccentricity and inclination: application to Mercury orbiter

We hereby study the stability of a massless probe orbiting around an oblate central body (planet or planetary satellite) perturbed by a third body, assumed to lie in the equatorial plane (Sun or Jupiter for example) using an Hamiltonian formalism. We are able to determine, in the parameters space, the location of the frozen orbits, namely orbits whose orbital elements remain constant on average, to characterize their stability/unstability and to compute the periods of the equilibria. The proposed theory is general enough, to be applied to a wide range of probes around planet or natural planetary satellites. The BepiColombo mission is used to motivate our analysis and to provide specific numerical data to check our analytical results. Finally, we also bring to the light that the coefficient J_2 is able to protect against the increasing of the eccentricity due to the Kozai-Lidov effect.

The NSDB natural satellites astrometric database

<i>Context. <i/>Any study of the dynamics of the Natural Planetary satellites needs to gather as many astrometric observations as possible of those that have been observed for centuries. This kind of work is partially made by each astronomer starting this kind of study but has never been done for all the satellite systems.<i>Aims. <i/>The goal of our work is to build a database of all the available astrometric observations, together with all the information needed for efficient use of these data, and to avoid astronomers interested in the dynamics of Planetary satellites have to redo this data search.<i>Methods. <i/>To do this we had to find and carefully read all the publications including observational data, international journals, or internal reports to be able to add the observations in the database knowing the reference frame used by the observer, the corrections and reduction made, and the time scale needed to link all the data. We also had to contact observatories and observers to be sure to have the raw data available. We gathered the bibliographic references related to the observations put in the database.<i>Results. <i/>A new database containing about 90 percent of all the observations useful for studying the dynamics of the satellites is now available for the interested community of astronomers. NSDB is accessible on the Internet: http://www.imcce.fr/nsdc (IMCCE) and http://lnfm1.sai.msu.ru/neb/nss/nssnsdcme.htm (trilingual version of SAI).

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 1997: Astrometric results of observations

In 2006, a complete database of the international campaign on photometric observations of the Galilean satellites of Jupiter in the 1997 epoch of mutual occultations and eclipses was published. Only two thirds of the observations were considered by other authors beforehand. In this study, we have processed the whole observational database with an original technique in order to obtain the astrometric data. We determined 301 relative positions of the satellites from photometric observations performed at 50 observatories around the world. The results are put into a common database of all observations of the natural planetary satellites called the Natural Satellites Data Center (NSDC) available on the Internet site http://www.sai.msu.ru/neb/nss/index.htm. The influence of random and systematic errors on the accuracy of determining the coordinates of satellites has been analyzed. It has been shown that the largest systematic errors are caused by inaccurate elimination of the background of the photometric measurements and by the erroneous data on the albedo of satellites. The actual accuracy of astrometric results is 0.05″ and 0.07″ in right ascension and declination, respectively. New recommendations for photometric observations of satellites during the considered phenomena have been developed in order to avoid the systematic errors.

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002-2003: final astrometric results

The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events. This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data. We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites. We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms ‘O-C’ residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17.

The natural satellites ephemerides facility MULTI-SAT

Context. There is a need in some research facilities for deriving ephemerides, controlling observations, verifying various models of motion, and calculating the coordinates in space of natural planetary satellites. Aims. The goal of our work is to elaborate the ephemerides of all natural satellites based upon all observations available to date and readily accessible for any user via the Internet. Methods. For all outer planetary satellites, original numerical models of motion are used that are based on all published observations. For other satellites, the theoretical models of the motion are taken from publications that are as recent as possible. Complete collection of the theories and models of motion is realized as a software for the ephemerides of natural satellites available on the web pages of the so-called server MULTI-SAT. Results. A new facility for producing ephemerides of all natural satellites of planets (except the Moon) has been created at IMCCE and SAI. Special features of the ephemerides are realized, such as predicting the phenomena and providing configurations useful for the observers. The server MULTI-SAT is accessible through the Internet. The URL addresses are http://www.imcce.fr/sat (English and French versions at IMCCE) and http://www.sai.msu.ru/neb/nss/index.htm (English, French, and Russian versions at SAI). This paper includes a complete review of the most precise theories of motion of all natural satellites that we used and an analysis of the precision of the proposed ephemerides.

Astrometric results of observations of mutual occultations and eclipses of the Galilean satellites of Jupiter in 2003

Context. The photometry of mutual occultations and the eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by analyzing the light curves of the satellites observed during these mutual events. Aims. The final goal of observations is to refine the models of motion for the natural satellites, and to develop a very accurate photometric model of mutual occultations and eclipses of satellites. This paper is focusing on the differences of topocentric or heliocentric coordinates of satellites pairs by analyzing the photometry of mutual occultations and the eclipses of natural satellites. Methods. We propose the most accurate photometric model of mutual events to date based on all available data about the satellites, and have developed the corresponding method for extracting astrometric data. We analyze the errors of astrometric results obtained in terms of different scattering laws allowing for reflecting properties of the satellites surfaces. In addition we consider how to allow various previously neglected effects. Results. We describe the results obtained by applying our method to observations of mutual occultations and eclipses of the Galilean satellites of Jupiter made in 2002–2003. We show that the coordinate errors due to irreducible systematic errors of photometry are about the same as the errors introduced by neglecting the above effects. We find the available maps of satellites surfaces to be unsuitable for deriving photometric event models.

A Method for Reducing Photometric Observations of Mutual Occultations and Eclipses of Planetary Satellites

Photometry of mutual occultations and eclipses of natural planetary satellites allows accurate astrometric data to be obtained by reducing the derived light curves of the satellites. In contrast to commonly used techniques by which the differences between the topocentric angular coordinates of satellites are deduced, we suggest a new approach and develop a corresponding method. To simplify the use of photometric data, the differences between the planetocentric rectangular coordinates of the two satellites at one time are deduced in the new method from each light curve. The advantages of this approach are that after such an observational data reduction, it will suffice to consider only the planetocentric motion of the satellites to improve their orbital parameters.

On the chaotic rotation of planetary satellites: The Lyapunov spectra and the maximum Lyapunov exponents

The possibility of dynamic chaos in the spin motion of minor natural planetary satellites is studied numerically and analytically. A satellite is modelled as a tri-axial rigid body in a fixed elliptic orbit. The Lyapunov characteristic exponents (LCEs) are used as indicators of the degree of chaos of the motion. For a set of real satellites (i.e. satellites with actual values of inertial and orbital parameters), the full Lyapunov spectra of the chaotic rotation are computed by the HQR-method of von Bremen et al. (1997). A more traditional shadow trajectory method for the computation of maximum LCEs is also used. Numerical LCEs obtained in the spatial and planar cases of chaotic rotation are compared to analytical estimates obtained by the separatrix map theory in the model of nonlinear resonance (here: synchronous spin-orbit resonance) as a perturbed nonlinear pendulum (Shevchenko 2000a, 2002). Further evidence is given that the agreement of the numerical data with the separatrix map theory in the planar case is very good. It is shown that the theory developed for the planar case is most probably still applicable in the case of spatial rotation, if the dynamical asymmetry of the satellite is suciently small or/and the orbital eccentricity is relatively large (but, for the dynamical model to be valid, not too large). The theoretical implications are discussed, and simple statistical dependences of the components of the LCE spectrum on the parameters of the problem are derived.

Maximum Lyapunov Exponents for Chaotic Rotation of Natural Planetary Satellites

Based on the Chirikov approach [1, 2] within the context of the theory of separatrix mappings, we suggest and substantiate a simple method for estimating the maximum Lyapunov characteristic exponent (MLCE) of motion in a chaotic layer in the neighborhood of nonlinear resonance separatrix of a Hamiltonian system under an asymmetric periodic perturbation. For a number of natural planetary satellites, using this method, the estimates are made of the MLCE of chaotic rotation (relative to the center of mass) in the main chaotic layer, i.e., in the chaotic layer in the neighborhood of a synchronous resonance separatrix. The value of the MLCE is determined by an orbital eccentricity and by the parameter of the satellite's dynamic asymmetry. The quantity inverse to the MLCE gives a typical time of predictable rotational motion.

Bifurcation Regime of a Synchronous Resonance in the Translational–Rotational Motion of Nonspherical Natural Satellites of Planets

Period-doubling bifurcations of the synchronous spin-orbit resonance in the motion of a nonspherical natural planetary satellite along the elliptic orbit are studied. The satellite spin axis is assumed to coincide with the axis of its largest principal moment of inertia and is perpendicular to the orbital plane. The period-doubling bifurcations take place when the value of satellite's dynamical asymmetry parameter falls in the parametric resonance domain. Theoretical dependences of the amplitude of the bifurcation oscillations of a satellite at the pericenter of its orbit upon the eccentricity and dynamical asymmetry parameter are investigated. Three different methods of calculating the amplitude of bifurcation oscillations are presented and compared. These theoretical estimates can be used to predict the opportunity to observe the bifurcation regime. The possibility of the occurrence of the bifurcation regime in the motion of natural planetary satellites is studied. It is concluded that the bifurcation regime is possible in the motion of Deimos, Epimetheus, Helen, Pandora, and Phobos. Phobos is the most probable candidate for finding the bifurcation regime of a synchronous rotation. The identification of such a regime would allow one to impose stringent constraints on the values of the inertial parameters of the satellite observed.

The 1997 Campaign of Observations of Mutual Occultations and Eclipses in the System of Jupiter's Galilean Satellites: Final Results

This paper presents the final results of the campaign of photometric observations of the Galilean satellites of Jupiter at the time of their mutual occultations and eclipses at the epoch of 1997 at observatories of Kazakhstan, Russia, and Ukraine. These results essentially contribute to the worldwide database of this type. They will help to refine the models of motion of the Galilean satellites of Jupiter. A comparison is made of the obtained data with the results of the worldwide campaign of observations of mutual occultations and eclipses in 1997. From the results of these observations, the differences of planetocentric coordinates of two satellites are calculated for a sequence of instants of time. Processing is based on the theory and the model of mutual occultations and eclipses of natural planetary satellites, which were developed by one of the authors in previous papers (Emel'yanov, 1999, 2000). In this paper, some new elements of the technique were used. We estimated the accuracy of observations. The paper contains information on the observing conditions and describes briefly the instruments employed.

Visible Encounters of the Outermost Satellites of Jupiter

Abstracts—A special method of ground-based observations of natural planetary satellites is described. A higher accuracy of observations is reached at the periods of their visible encounters as two satellites fall within the same CCD frame. For the outermost natural satellites, such events are very rare. The circumstances of the visible encounters of the outermost satellites of Jupiter are precalculated for two years to come and are presented in this paper. The observations of these satellites are particularly important in solving the problems connected with the origin and evolution of small bodies in the Solar System.

Eclipses of natural planetary satellites

A general method is given for predicting eclipse events for natural planetary satellites suitable for use on a large scale digital computer. The precision is sufficient to process photometric eclipse observations to improve natural satellite ephemerides. Expected accuracy improvement for Saturn's satellites should be an order of magnitude or better. Predicted eclipse times of satellites by Saturn and the Rings are given for the next decade.