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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.

Context. The accuracy of predicted orbital positions depends on the quality of the theorical model and of the observations used to fit the model. During the period of observations, this accuracy can be estimated through comparison with observations. Outside this period, the estimation remains difficult. Many methods have been developed for asteroid ephemerides in order to evaluate this accuracy.

We present new ephemerides of Phobos and Deimos that are fit to observations from 1877 to 2005 and include recent spacecraft observations by Mars Global Surveyor and Mars Express. In contrast to earlier models, this is the first completely numerical one. In particular, the tidal effects have been modeled by the tidal bulge raised by each moon on the planet, instead of fitting secular accelerations in the satellite longitudes. This partly avoids absorbing the Deimos observational errors in its related tidal acceleration. Moreover, applying this model to other systems will be easier. Our estimate of the Martian dissipation is Q= 79.91±0.69 (1σ-formal error) when assuming $k_2 = 0.152$for the Martian Love number and $G{m}_{\rm Ph}$= 0.68$\times$106m3/s2for the Phobos mass. We also report the possibility of fitting the Phobos oblateness gravity field. We suspect a non-uniform density for Phobos or a bias in either the observations or the Martian gravity field. A FORTRAN subroutine that computes the Martian moons' ephemerides is available on request.

Aims.We aim to provide a synthetic representation of the orbital motion of Io, Europa, Ganymede, and Callisto. It corresponds to a quasi-periodic Fourier series whose arguments are integer combinations of the fundamental arguments of the dynamical system, which are also given.

Context.Every 42 years, the Earth and the Sun pass through the equatorial plane of Uranus allowing observations of mutual occultations and eclipses of the main satellites of Uranus. The next opportunity will occur in 2006–2009.

We present a new model of the four Galilean satellites Io, Europa, Ganymede and Callisto, able to deliver accurate ephemerides over a very long time span (several centuries). In the first paper (Lainey et al. [CITE], A&A, 420, 1171) we gave the equations of the dynamical model. Here we present the fit of this model to the observations, covering more than one century starting from 1891. Our ephemerides, based on this first fit called L1, are available on the web page of the IMCCE at the URL http://www.imcce.fr/ephemeride_eng.html.

We present a new theory of the four Galilean satellites Io, Europa, Ganymede and Callisto. This theory aims to deliver highly accurate ephemerides able to represent the Galilean satellites' motion over several centuries. It is based on the numerical integration of elaborated equations of motion. This first paper describes and tests many usually neglected perturbations. We are then able to retain some of them in the dynamical model for the Galilean system. A numerical method developed to adjust the model to the observations is given. We used a general formalism so it can be extended to systems other than the Galilean one. As an example of this method, we compare our model to the current E5 ephemerides of the four Galileans.

Astrometric results of observations of the mutual events of the Galilean satellites of Jupiter of the PHEMU97 campaign by the Institut de Mécanique Céleste et de Calcul des Éphémérides are presented. These astrometric positions can be directly utilized in the construction of future ephemerides. We attempt here to compare the residuals of the relative astrometric positions of satellites with respect to the E3, G5, E5 and L1 ephemerides. The model to fit the observed light curves includes the intensity variations on the surface of satellites using the mosaics constructed by the teams at the US Geological Survey from Voyager and Galileo imagery.

Context. In 2003, the Sun and the Earth passed through both the equatorial plane of Jupiter and therefore the orbital planes of its main satellites. Aims. During this period, mutual eclipses and occultations were observed and we present the data collected.Methods. Light curves of mutual eclipses and occultations were recorded by the observers of the international campaign PHEMU03 organized by the Institut de m?canique c?leste, Paris, France. Results. We completed 377?observations of 118?mutual events from 42?sites and the corresponding data are presented in this paper. For each observation, information about the telescope, receptor, site, and observational conditions are provided.Conclusions. This paper gathers all data and indicates a first estimate of its precision. This catalogue of these rare events should constitute an improved basis for accurate astrometric data useful in the development of dynamical models.

Observations of the predicted occultation between the satellites Miranda and Oberon were performed on 2007 July 30. Data analysis reveals that the predicted magnitude drop for this phenomenon was overestimated and we establish an upper limit of 0m. 05 for the phenomenon, perhaps due to a nonlambertian limb scattering. The new astrometry obtained from this run is in good agreement with the LA06 numerical model and these new data will improve the dynamical models of the Uranus system. The paper concludes with an uncertainty analysis on the parameters for the event, determined by the uncertainty of the magnitude drop of about 0.04 mag, and the difficulty to observe mutual phenomena between satellites in the Uranian system. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim

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.

Context. The EUROpean Near Earth Asteroid Research (EURONEAR) is a network which envisions to bring some European contributions into the general context traced by the Spaceguard Foundation which was carried out during the last 15 years mainly by the US with some modest European and amateur contributions. Aims. The number of known near Earth asteroids (NEAs) and potentially hazardous asteroids (PHAs) has increased tremendously, mainly thanks to five major surveys all focused on the discovery of new bodies. But also other facilities are required to follow-up and improvement the orbital parameters and to study the physical properties of the known bodies. These goals are better achieved by a co-ordinated network such as EURONEAR. Methods. Astrometry is mandatory in order to acquire the positional information necessary to define and improve orbits of NEAs and PHAs and to study their trajectories through the solar system, especially in the vicinity of Earth. Photometry is required to derive some physical information about NEAs and PHAs. In order to achieve these objectives, the main method of research of the EURONEAR is the follow-up programme of objects selected by a few criteria, carried out mostly at 1 m-class telescopes endowed with medium and large field cameras. Results. 162 NEAs summing more than 1500 individual positions were observed for a total time of 55 nights in both visiting mode and regular runs using nine telescopes located in four countries. The observations were reduced promptly and reported to the Minor Planet Centre (MPC) which validated and included them in the MPC and NEODyS databases following the improvement of their orbital elements. For one binary NEA we acquired photometry and were able to determine its orbital and rotational periods. Complementary to the follow-up work, as many as 500 unknown moving objects consistent with new Main Belt asteroids and one possible NEA were discovered in the analyzed fields. Conclusions. Our positions present 1$\arcsec$precision with an accuracy of 0.2–0.4$\arcsec$, sufficient for achieving our immediate main goals. The observations and data reduction were conducted by our network members, which included some students and amateurs supervised by professional astronomers. In most cases, we increased the observational arcs decreasing the uncertainties in the orbits, while in some cases the new positions allowed us to recover some bodies endangered to be lost, defining their orbits.

Context. The EUROpean Near Earth Asteroid Research (EURONEAR) is a network which envisions to bring some European contributions into the general context traced by the Spaceguard Foundation which was carried out during the last 15 years mainly by the US with some modest European and amateur contributions.