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The Karner blue butterfly (Lycaeides melissa samuelis) (hereafter Karner blue) is a federally listed endangered species occurring in disjunct locations within the Midwest and Eastern United States. As a hostplant specialist and an ectotherm, the Karner blue is likely to be susceptible to effects of climate change. We undertook warming experiments to explore the temperature sensitivity of various Karner blue life history stages and traits. Over a two-year period, we exposed all Karner blue life stages to temperature increases of + 2, + 4, and + 6 °C above 1952–1999 mean temperatures. We analyzed the effect of these treatments on life history parameters likely related to fitness and population size, including development time, voltinism, degree-day accumulation, body weight, and morphology. Warming treatments resulted in earlier emergence and accelerated development, leading to additional generations. Warming also increased the number of degree-days accumulated during pre-adult development (i.e., egg hatch to eclosion). Results suggest that Karner blues developed in fewer days, in part, by putting on less mass as temperatures increased. As treatment temperature increased, adult body mass, length, and area decreased and voltinism increased. Females with lower adult mass and smaller body size produced fewer eggs. These results suggest a trade-off between accelerated development and decreased body size with decrease in adult mass and abdominal area being associated with reduced fecundity. Implications for insect conservation: Changes in development timing and in voltinism can negatively affect phenological matching between the Karner blue and its obligate host plant, Wild lupine (Lupinus perennis), resulting in population decrease. Poorer phenological matching between insect and hostplant can occur across multiple generations, for example, negatively affecting overwintering population size. With increasing temperatures, smaller females will produce fewer eggs, which can also lead to poorer population outcomes across generations. [ABSTRACT FROM AUTHOR]

Context. The upcoming JUICE and Europa Clipper missions targeting Jupiter's Galilean satellites will provide radio science tracking measurements of both spacecraft. Such data are expected to significantly help estimating the moons' ephemerides and related dynamical parameters (e.g. tidal dissipation parameters). However, the two missions will yield an imbalanced dataset, with no flybys planned at Io, condensed over less than six years. Current ephemerides' solutions for the Galilean moons, on the other hand, rely on ground-based astrometry collected over more than a century which, while being less accurate, bring very valuable constraints on the long-term dynamics of the system. Aims. An improved solution for the Galilean satellites' complex dynamics could however be achieved by exploiting the existing synergies between these different observation sets. Methods. To quantify this, we merged simulated radio science data from both JUICE and Europa Clipper spacecraft with existing ground-based astrometric and radar observations, and performed the inversion in different configurations: either adding all available ground observations or individually assessing the contribution of different data subsets. Our discussion specifically focusses on the resulting formal uncertainties in the moons' states, as well as Io's and Jupiter's tidal dissipation parameters. Results. Adding astrometry stabilises the moons' state solution, especially beyond the missions' timelines. It furthermore reduces the uncertainties in 1/Q (inverse of the tidal quality factor) by a factor two to four for Jupiter, and about 30–35% for Io. Among all data types, classical astrometry data prior to 1960 proved particularly beneficial. Overall, we also show that ground observations of Io add the most to the solution, confirming that ground observations can fill the lack of radio science data for this specific moon. Conclusions. We obtained a noticeable solution improvement when making use of the complementarity between all different observation sets. The promising results obtained with simulations thus motivate future efforts to achieve a global solution from actual JUICE and Clipper radio science measurements. [ABSTRACT FROM AUTHOR]

Moons potentially harbouring a global ocean are tending to become relatively common objects in the Solar System1. The presence of these long-lived global oceans is generally betrayed by surface modification owing to internal dynamics2. Hence, Mimas would be the most unlikely place to look for the presence of a global ocean3. Here, from detailed analysis of Mimas’s orbital motion based on Cassini data, with a particular focus on Mimas’s periapsis drift, we show that its heavily cratered icy shell hides a global ocean, at a depth of 20–30 kilometres. Eccentricity damping implies that the ocean is likely to be less than 25 million years old and still evolving. Our simulations show that the ocean–ice interface reached a depth of less than 30 kilometres only recently (less than 2–3 million years ago), a time span too short for signs of activity at Mimas’s surface to have appeared.An analysis of the orbital motion of Saturn’s moon Mimas shows that a recently formed global subsurface ocean lies beneath its cratered icy shell and that this ocean is probably still evolving. [ABSTRACT FROM AUTHOR]

Ephemerides of planetary satellites require regular updates to take into account new observations of the satellites. Such revision has been all the more necessary in the case of outer planetary satellites, since a number of new moons have been discovered recently. Thus, we present updated versions of the ephemerides of the outer planetary satellites. The problem and the methodology for estimating ephemeris accuracy are discussed. Comparison with the Jet Propulsion Laboratory (JPL) ephemerides proves that the accuracy depends largely on the distribution of the observations. We give examples where, for a few satellites, the O−C residuals increase sharply at time intervals lying significantly beyond the time interval of observations used to generate the ephemerides. This fact alone indicates that there is an urgent need for new observations. Besides the ephemerides of moons, which can be accessed online via the MULTI-SAT server, we provide orbital parameters for the recently discovered faint satellites of Jupiter and Saturn. The problems discussed in this work are important for planning space observations of the outer satellites by future space missions like the European Space Agency (ESA) JUpiter ICy moons Explorer (JUICE) and National Aeronautics and Space Administration (NASA) Europa Clipper missions. [ABSTRACT FROM AUTHOR]

In the caviar software package, a standard tool for astrometry of images from the Cassini imaging science subsystem (ISS), Gaussian fitting is used to measure the centre of point-like objects, achieving a typical precision of about 0.2 pixels. In this work, we consider how alternative methods may improve on this. We compare three traditional centroiding methods: two-dimensional Gaussian fitting, median, and modified moment. Results using 56 selected images show that the centroiding precision of the modified moment method is significantly better than the other two methods, with standard deviations for all residuals in sample and line of 0.065 and 0.063 pixels, respectively, representing a factor of over 2 improvement compared to Gaussian fitting. Secondly, a comparison of observations using Cassini ISS images of Anthe is performed. Anthe results show a similar improvement. The modified moment method is then used to reduce all ISS images of Anthe during the period 2008–2017. The observed-minus-calculated residuals relative to the JPL SAT393 ephemeris are calculated. In terms of α × cos(δ) and δ in the Cassini-centred international celestial reference frame, mean values of all residuals are close to 0 km, and their standard deviations are less than 1 km for narrow angle camera images, and about 4 km for wide angle camera images. [ABSTRACT FROM AUTHOR]

The resource concentration hypothesis predicts that herbivorous insect density scales positively with plant density because insects are better able to identify, and remain longer in, patches with denser plant resources. While some studies support this hypothesis, others do not. Different explanations have been proposed for this discrepancy, including variation in insect dispersal ability and diet breadth. We test the resource concentration hypothesis using the Karner blue butterfly (Lycaeides melissa samuelis), a specialist that relies on wild blue lupine (Lupinus perennis) as its sole host plant. We extended this hypothesis to test whether Karner blue density also scales positively with nectar plant resources. Our findings did not support the resource concentration hypothesis and demonstrate that the spatial segregation of nectar and host plant resources relative to each other can influence the location and abundance of Karner blues on the landscape. This is because the location of resources relative to each other influences the energy and time butterflies expend for flight activity, and thereby influences resource acquisition. During early summer when first brood Karner blues emerge, nectar and host plants were spatially segregated, and Karner blue density peaked at intermediate densities of nectar and host plants occurring at ratios approximately equal to 1:1. During late summer, we found no significant relationships between second brood Karner blues and nectar plants or host plants when there was no correlation between nectar and host plants. Conservation practitioners of specialist insects with low vagility can strategically manage the distribution of plant resources to minimize insect time and energy expenditure and promote resource acquisition for all of an insect's life stages. [ABSTRACT FROM AUTHOR]

This study is a companion paper to Baillié et al. in which we showed that a past episode of inward migration of Mimas could have created the Cassini Division. We here investigate the possible causes of this inward migration. We suggest two scenarios: one based on a past intense heating of Mimas, and another one on a past intense heating of Enceladus, which would have itself driven an inward migration of Mimas due to a mean-motion resonance. These two scenarios are challenged with numerical modelling of the orbital motion of the satellites, and energy budget, which are confronted to our present knowledge of the interior of Mimas and Enceladus. We show that a past hot Mimas requires an eccentricity of 0.22, while a past hot Enceladus would have needed an eccentricity of 0.25. While the scenario of a past hot Mimas preserves the stability of the mid-sized satellites of Saturn, it threatens Janus and Epimetheus and is inconsistent with the observations of impact basins at the surface of Mimas. However, a past hot Enceladus which would have almost fully melted could be consistent with its differentiated interior, but would probably not have preserved the stability of Tethys, given the high eccentricity required. Both of these scenarios would have challenged the stability of Aegaeon, Methone, Pallene, and Anthe, and implied that the Cassini Division would be younger than 10 Myr. [ABSTRACT FROM AUTHOR]

Context. Bright stellar positions are now known with an uncertainty below 1 mas thanks to Gaia DR2. Between 2019–2020, the Galactic plane will be the background of Jupiter. The dense stellar background will lead to an increase in the number of occultations, while the Gaia DR2 catalogue will reduce the prediction uncertainties for the shadow path. Aims. We observed a stellar occultation by the Galilean moon Europa (J2) and propose a campaign for observing stellar occultations for all Galilean moons. Methods. During a predicted period of time, we measured the light flux of the occulted star and the object to determine the time when the flux dropped with respect to one or more reference stars, and the time that it rose again for each observational station. The chords obtained from these observations allowed us to determine apparent sizes, oblatness, and positions with kilometre accuracy. Results. We present results obtained from the first stellar occultation by the Galilean moon Europa observed on 2017 March 31. The apparent fitted ellipse presents an equivalent radius of 1561.2 ± 3.6 km and oblatenesses 0.0010 ± 0.0028. A very precise Europa position was determined with an uncertainty of 0.8 mas. We also present prospects for a campaign to observe the future events that will occur between 2019 and 2021 for all Galilean moons. Conclusions. Stellar occultation is a suitable technique for obtaining physical parameters and highly accurate positions of bright satellites close to their primary. A number of successful events can render the 3D shapes of the Galilean moons with high accuracy. We encourage the observational community (amateurs included) to observe the future predicted events. [ABSTRACT FROM AUTHOR]

The technique of mutual approximations accurately gives the central instant of the maximum apparent approximation of two moving natural satellites in the plane of the sky. This can be used in ephemeris fitting to infer the relative positions of satellites with high precision. Only mutual phenomena – occultations and eclipses – can achieve better results. However, mutual phenomena only occur every six years in the case of Jupiter. Mutual approximations do not have this restriction and can be observed at any time in the year as long as the satellites are visible. In this work, we present 104 central instants determined from the observations of 66 mutual approximations between the Galilean moons carried out at different sites in Brazil and France during the period 2016–2018. For 28 events, we have at least two independent observations. All telescopes were equipped with a narrow-band filter centred at 889 nm with a width of 15 nm to eliminate the scattered light from Jupiter. The telescope apertures ranged between 25 and 120 cm. For comparison, the precision of the positions obtained with classical CCD astrometry is about 100 mas, for mutual phenomena it can be 10 mas or less, and the average internal precision obtained with mutual approximations is 11.3 mas. This new type of simple, yet accurate, observations can significantly improve the orbits and ephemeris of Galilean satellites and thus it can be very useful for the planning of future space missions to the Jovian system. [ABSTRACT FROM AUTHOR]

We provide new astrometric observations of Enceladus from images taken using the Cassini Imaging Science Subsystem (ISS) Narrow-Angle Camera. Astrometric reduction was performed using a new fully automatic camera repointing technique built within the Caviar software package. The new automatic procedure is based on the k-d tree technique and has been developed as an alternative to the manual technique currently available in Caviar. We describe the new procedure and demonstrate its effectiveness compared with manual processing. Repointing corrections were computed using reference stars from the UCAC4 and Gaia DR1 star catalogues. We compare the observed-minus-computed (O−C) residuals of Enceladus based on UCAC4 with those based on Gaia DR1, relative to the JPL SAT375 ephemeris and the IMCCE NOE ephemeris, respectively. We reduced all available Cassini ISS images of Enceladus during the period 2013–2017, producing a total of 1109 Cassini -centred astrometric observations. These are provided in right ascension (α) and declination (δ) in the International Celestial Reference Frame (ICRF). Estimated mean O−C residuals relative to JPL's SAT375 ephemeris were 0.7 km in α  × cos(δ) and 1.8 km in δ, with standard deviations of 2.4 and 3.2 km, respectively. No improvement in the precision of the observations was obtained when using the GAIA DR1 star catalogue compared with UCAC4. [ABSTRACT FROM AUTHOR]

Aims. Caviar is a software package designed for the astrometric measurement of natural satellite positions in images taken using the Imaging Science Subsystem (ISS) of the Cassini spacecraft. Aspects of the structure, functionality, and use of the software are described, and examples are provided. The integrity of the software is demonstrated by generating new measurements of the positions of selected major satellites of Saturn, 2013–2016, along with their observed minus computed (O−C) residuals relative to published ephemerides. Methods. Satellite positions were estimated by fitting a model to the imaged limbs of the target satellites. Corrections to the nominal spacecraft pointing were computed using background star positions based on the UCAC5 and Tycho2 star catalogues. UCAC5 is currently used in preference to Gaia-DR1 because of the availability of proper motion information in UCAC5. Results. The Caviar package is available for free download. A total of 256 new astrometric observations of the Saturnian moons Mimas (44), Tethys (58), Dione (55), Rhea (33), Iapetus (63), and Hyperion (3) have been made, in addition to opportunistic detections of Pandora (20), Enceladus (4), Janus (2), and Helene (5), giving an overall total of 287 new detections. Mean observed-minus-computed residuals for the main moons relative to the JPL SAT375 ephemeris were − 0.66 ± 1.30 pixels in the line direction and 0.05 ± 1.47 pixels in the sample direction. Mean residuals relative to the IMCCE NOE-6-2015-MAIN-coorb2 ephemeris were −0.34 ± 0.91 pixels in the line direction and 0.15 ± 1.65 pixels in the sample direction. The reduced astrometric data are provided in the form of satellite positions for each image. The reference star positions are included in order to allow reprocessing at some later date using improved star catalogues, such as later releases of Gaia, without the need to re-estimate the imaged star positions. [ABSTRACT FROM AUTHOR]

Context. The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency’s Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet–satellite systems. Aims. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. Methods. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. Results. We achieved, on average, mHz precision (30 µm/s at a 10 s integration time) for radial three-way Doppler estimates and sub-nanoradian precision for lateral position measurements, which in a linear measure (at a distance of 1.4 AU) corresponds to ∼50 m. [ABSTRACT FROM AUTHOR]

Context. The irregular satellites of the giant planets are believed to have been captured during the evolution of the solar system. Knowing their physical parameters, such as size, density, and albedo is important for constraining where they came from and how they were captured. The best way to obtain these parameters are observations in situ by spacecrafts or from stellar occultations by the objects. Both techniques demand that the orbits are well known. Aims. We aimed to obtain good astrometric positions of irregular satellites to improve their orbits and ephemeris. Methods. We identified and reduced observations of several irregular satellites from three databases containing more than 8000 images obtained between 1992 and 2014 at three sites (Observatório do Pico dos Dias, Observatoire de Haute-Provence, and European Southern Observatory - La Silla). We used the software Platform for Reduction of Astronomical Images Automatically (PRAIA) to make the astrometric reduction of the CCD frames. The UCAC4 catalog represented the International Celestial Reference System in the reductions. Identification of the satellites in the frames was done through their ephemerides as determined from the SPICE/NAIF kernels. Some procedures were followed to overcome missing or incomplete information (coordinates, date), mostly for the older images. Results. We managed to obtain more than 6000 positions for 18 irregular satellites: 12 of Jupiter, 4 of Saturn, 1 of Uranus (Sycorax), and 1 of Neptune (Nereid). For some satellites the number of obtained positions is more than 50% of what was used in earlier orbital numerical integrations. Conclusions. Comparison of our positions with recent JPL ephemeris suggests there are systematic errors in the orbits for some of the irregular satellites. The most evident case was an error in the inclination of Carme. [ABSTRACT FROM AUTHOR]

Context. The Cassini spacecraft has been orbiting Saturn since 2004 and has returned images of satellites with an astrometric resolution as high as a few hundred meters per pixel. Aims. We used the images taken by the Narrow Angle Camera (NAC) of the Image Science Subsystem (ISS) instrument on board Cassini, for the purpose of astrometry. Methods. We applied the same method that was previously developed to reduce Cassini NAC images of Mimas and Enceladus. Results. We provide 5463 astrometric positions in right ascension and declination (α, δ) of the satellites: Tethys, Dione, Rhea, Iapetus, and Phoebe, using images that were taken by Cassini NAC between 2004 and 2012. the mean residuals compared to the JPL ephemeris SAT365 are of the order of hundreds of meters with standard deviations of the order of a few kilometers. The frequency analysis of the residuals shows the remaining unmodelled effects of satellites on the dynamics of other satellites. [ABSTRACT FROM AUTHOR]

Context. Accurate positional measurements of planets and satellites are used to improve our knowledge of their dynamics and to infer the accuracy of planet and satellite ephemerides. Aims. In the framework of the FP7 ESPaCE project, we provide the positions of Mars, Phobos, and Deimos taken with the U.S. Naval Observatory 26-inch refractor during the 1971 opposition of the planet. Methods. These plates were measured with the digitizer of the Royal Observatory of Belgium and reduced through an optimal process that includes image, instrumental, and spherical corrections to provide the most accurate data. Results. We compared the observed positions of the planet Mars and its satellites with the theoretical positions from INPOP10 and DE430 planetary ephemerides, and from NOE and MAR097 satellite ephemerides. The rms residuals in RA and Dec of one position is less than 60 mas, or about 20 km at Mars. This accuracy is comparable to the most recent CCD observations. Moreover, it shows that astrometric data derived from photographic plates can compete with those of old spacecraft (Mariner 9, Viking 1 and 2). [ABSTRACT FROM AUTHOR]

Aims. We provide astrometric observations of two of Saturn's main satellites, Mimas and Enceladus, using high resolution Cassini ISS Narrow Angle Camera images. Methods. We developed a simplified astrometric reduction model for Cassini ISS images as an alternative to the one proposed by the Jet Propulsion Laboratory (JPL). The particular advantage of the new model is that it is easily invertible, with only marginal loss in accuracy. We also describe our new limb detection and fitting technique. Results. We provide a total of 1790 Cassini-centred astrometric observations of Mimas and Enceladus, in right ascension (α) and declination (δ) in the International Celestial Reference Frame (ICRF). Mean residuals compared to JPL ephemerides SAT317 and SAT351 of about one kilometre for Mimas and few hundreds of metres for Enceladus were obtained, in α cos δ and δ, with a standard deviation of a few kilometres for both satellites. A frequency analysis of the residuals revealed some periodic variability in the right ascension for Mimas. An additional analysis of Mimas' mean longitude suggests that some short-period terms are missing in the TASS orbital model. [ABSTRACT FROM AUTHOR]

This paper deals with tests of general relativity (GR) in the Solar System using tracking observables from planetary spacecraft. We present a new software that simulates the Range and Doppler signals resulting from a given spacetime metric. This flexible approach allows one to perform simulations in GR as well as in alternative metric theories of gravity. The outputs of this software provide templates of anomalous residuals that should show up in real data if the underlying theory of gravity is not GR. Those templates can be used to give a rough estimation of constraints on additional parameters entering alternative theory of gravity and also signatures that can be searched for in data from past or future space missions aiming at testing gravitational laws in the Solar System. As an application of the potentiality of this software, we present some simulations performed for Cassini-like mission in post-Einsteinian gravity and in the context of MOND external field effect. We derive signatures arising from these alternative theories of gravity and estimate expected amplitudes of the anomalous residuals. [ABSTRACT FROM AUTHOR]

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 Saturnian satellites made during the international campaign in 2009. The final goal is to derive new accurate astrometric data. Methods. We develop an accurate photometric model of mutual event observations of sufficiently high accuracy. Our original method is applied to derive astrometric data from photometric observations of the mutual occultations and eclipses of the Saturnian satellites. Results. We process the 26 light curves obtained during the international campaign of photometric observations of the Saturnian satellites in 2009. Compared with the theory TASS 1.7 by Vienne and Duriez, we find that the root mean square of the “O–C” residuals for the 23 highest quality observations are equal to 48.5 and 21.7 mas in right ascension and declination, respectively, we obtain 16.4 and 20.7 mas with the new theory by Lainey and collaborators and 17.3 and 21.6 mas with JPL SAT351 ephemerides. Topocentric or heliocentric angular differences for satellites pairs are obtained for 16 time instants during the time period from December 19, 2008 to July 16, 2009. [ABSTRACT FROM AUTHOR]

Context. Earth-like planets have viscoelastic mantles, whereas giant planets may have viscoelastic cores. The tidal dissipation of these solid regions, which are gravitationally perturbed by a companion body, strongly depends on their rheology and the tidal frequency. Therefore, modeling tidal interactions provides constraints on planets' properties and helps us to understand their history and evolution, in either our solar system or exoplanetary systems. Aims. We examine the equilibrium tide in the anelastic parts of a planet for every rheology, and by taking into account the presence of a fluid envelope of constant density. We show how to obtain the different Love numbers describing its tidal deformation, and discuss how the tidal dissipation in the solid parts depends on the planet's internal structure and rheology. Finally, we show how our results may be implemented to describe the dynamical evolution of planetary systems. Methods. We expand in Fourier series the tidal potential exerted by a point mass companion, and express the dynamical equations in the orbital reference frame. The results are cast in the form of a complex disturbing function, which may be implemented directly in the equations governing the dynamical evolution of the system. Results. The first manifestation of the tide is to distort the shape of the planet adiabatically along the line of centers. The response potential of the body to the tidal potential then defines the complex Love numbers, whose real part corresponds to the purely adiabatic elastic deformation and the imaginary part accounts for dissipation. The tidal kinetic energy is dissipated into heat by means of anelastic friction, which is modeled here by the imaginary part of the complex shear modulus. This dissipation is responsible for the imaginary part of the disturbing function, which is implemented in the dynamical evolution equations, from which we derive the characteristic evolution times. Conclusions. The rate at which the system evolves depends on the physical properties of the tidal dissipation, and specifically on (1) how the shear modulus varies with tidal frequency, (2) the radius, and (3) the rheological properties of the solid core. The quantification of the tidal dissipation in the solid core of giant planets reveals a possible high dissipation that may compete with dissipation in fluid layers. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we present 526 precise CCD positions of Galilean satellite-pairs of Jupiter, which have been extracted from 441 CCD frames captured by a 1-m telescope at the Yunnan Observatory from 2002 to 2010. The four Galilean satellites (Io, Europa, Ganymede and Callisto) are used to calibrate the CCD field of view by comparing their pixel positions with their theoretical positions computed from two modern ephemerides of the Galilean satellites, L2 and JUP230, which have been developed by the Institut de Méchanique Céleste et de Calcul des Éphémérides and the Jet Propulsion Laboratory, respectively. In this paper, we focus on the relative position of a pair of satellites with short separation (less than 85 arcsec) for good internal precision. The mean (O − C) (observed minus computed) values of all these satellite-pairs in right ascension and declination are found to be no larger than 6 mas and 2 mas, respectively, for each ephemeris. The estimated precision for one single observation is better than 30 mas in each direction. [ABSTRACT FROM AUTHOR]

BSTRACT [ABSTRACT FROM AUTHOR]

Evolutionary scenarios for the major satellites of Jupiter, Saturn, Neptune, and Pluto-Charon are discussed. In the Jovian system the challenge is to understand how the present Laplace resonance of Io, Europa, and Ganymede was established and to determine whether the heat being radiated by Io is in balance with the present tidal dissipation in the moon. In the Saturnian system, Enceladus and Titan are the centers of attention. Tidal heating is the likely source of activity at the south pole of Enceladus, although the details of how the heating occurs are not understood. An evolutionary scenario based on accretion and internal differentiation is presented for Titan, whose present substantial orbital eccentricity is not associated with any dynamical resonance. The source and maintenance of methane in Titan's present atmosphere remain uncertain. Though most attention on the Saturnian moons focuses on Titan and Enceladus, the mid-size satellites Iapetus, Rhea, Tethys, and the irregular satellite Phoebe also draw our interest. An evolutionary scenario for Iapetus is presented in which spin down from an early rapidly rotating state is called upon to explain the satellite's present oblate shape. The prominent equatorial ridge on Iapetus is unexplained by the spin down scenario. A buckling instability provides another possible explanation for the oblateness and equatorial ridge of Iapetus. Rhea is the only medium-size Saturnian satellite for which there are gravity data at present. The interpretation of these data are uncertain, however, since it is not known if Rhea is in hydrostatic equilibrium. Pluto and Charon are representative of the icy dwarf planets of the Kuiper belt. Did they differentiate as they evolved, and do either of them have a subsurface liquid water ocean? New Horizons might provide some answers when it arrives at these bodies. [ABSTRACT FROM AUTHOR]

When astrometric data can be extracted from archives, this generally allows us to get very strong constraints for the orbital modeling of Solar System objects. This is particularly important for Near-Earth Asteroids. We have developed tools in the Virtual Observatory framework in order to carry out such a task. We have applied them to the DENIS survey. This survey has been performed from 1995 to 2001 in the I, J, K' spectral bands with a 1m telescope at ESO La Silla. Many sources associated to Solar System Objects have been identified and we present our preliminary results. [ABSTRACT FROM PUBLISHER]

We studied small perturbations acting on Galilean satellites. Most of them are still not computed in the analytical theories and could probably improve the ephemeris of these satellites which are outside the precision of the observations. We used a numerical method to test the effect of such perturbations. Here are reporting the main results we obtained. [ABSTRACT FROM AUTHOR]

The Gaia DR1 catalogue stars are taken as reference ones to reduce the Cassini ISS images of Enceladus in 2015, and a total of 494 Cassini-centered astrometric observation are obtained in right ascension(α) and declination (δ) in the international Celestial Reference Frame(ICRF). Compared with JPL ephemerides SAT367, we derive that their mean residuals are a few tens meters in α*cos(δ) and a few kilometers in δ, and their standard deviation is not over 2 kilometers. Compared with the results from UCAC4 catalogue stars, The Gaia DR1 has the equivalent precision of reduction. [ABSTRACT FROM PUBLISHER]

The optical ground-based astrometry of solar system objects may have its accuracy strongly improved by using new methods for making observations and reductions of them. New photometric methods of observating the mutual phenomena occurring in the solar system, may provide astrometric data with a higher precision than the classical direct imaging. In order to help preparing observers for the future campaigns of observations (2008–2010) and to promote this kind of high-accuracy astrometry, we plan to organize a spring school in 2008 in Beijing, China, for PhD and post-doctoral students, and for interested young astronomers. [ABSTRACT FROM PUBLISHER]