Showing papers by "Nicolas Rambaux published in 2009"

Rotational Dynamics of Europa

Abstract: The rotational state of Europa is only rather poorly constrained at present. It is known to rotate about an axis that is nearly perpendicular to the orbit plane, at a rate that is nearly constant and approximates the mean orbital rate. Small departures from a constant rotation rate and oscillations of the rotation axis both lead to stresses that may influence the location and orientation of surface tectonic features. However, at present geological evidence for either of these processes is disputed. We describe a variety of issues that future geodetic observations will likely resolve, including variations in the rate and direction of rotation, on a wide range of timescales. Since the external perturbations causing these changes are generally well known, observations of the amplitude and phase of the responses will provide important information about the internal structure of Europa. We focus on three aspects of the rotational dynamics: obliquity, forced librations, and possible small departures from a synchronous rotation rate. Europa’s obliquity should be nonzero, while the rotation rate is likely to be synchronous unless lateral shell thickness variations occur. The tectonic consequences of a nonzero obliquity and true polar wander have yet to be thoroughly investigated.

The PHEMU03 catalogue of observations of the mutual phenomena of the Galilean satellites of Jupiter

Abstract: 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 mecanique celeste, 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.

Dynamically active Moon

Abstract: The lunar motion has been measured accurately for 39 years with Lunar Laser Ranging [1,2,3]. Today, the time-span of several decades and the accuracy of a few centimeters allow one to identify and characterize some geophysical mechanisms that influence the rotational motion.