185 research outputs found
supplementary data for Knibbe and Van Hoolst (2021)
No full textThis is supplementary data, and matlab code, for:
Knibbe J. S. and T. Van Hoolst (2021), Modelling of thermal stratification at the top of a planetary core: Application to the cores of Earth and Mercury and the thermal coupling with their mantles, Physics of the Earth and Planetary interiors, 106804
Updated Europa gravity field and interior structure from a reanalysis of Galileo tracking data
No full textThe Galileo radio tracking data were reanalysed exploiting the new knowledge of Jupiter obtained by the Juno mission, together with modern orbit determination techniques developed for the Cassini data analysis. Using Doppler data acquired during six encounters of Europa an updated gravity field of the moon was obtained, resulting in a value of C22 statistically different from the available literature. The new value suggests a thinner ice-water shell and a less dense interior
Influence of the internal structure of Europa on the Doppler signal of an orbiter
No full textEuropa, the second Galilean satellite starting from Jupiter, probably has a liquid ocean beneath the icy shell but the thickness of these layers is poorly known. From the values of the gravitational coefficients C20 and C22 of Europa determined by the Galileo mission, the to- tal thickness of the ice and water layer is evaluated to 80 - 170 km [1]. However, the thickness of the indi- vidual ice and water layers could not be determined, since their densities are similar. An important goal of the Europa Jupiter System Mission under study by NASA and ESA is to better constrain the ice shell and subsurface ocean of Eu- ropa. Important information on the interior structure is thought to result from observation of the tides, li- brations and obliquity of Europa. Here we assess the possibility to measure those quantities with a Radio Science instrument, which is part of the scientific core payload of the Europa orbiter of EJSM Together with the static gravity field of Europa, tides and rotation determine the orbital motion of a spacecraft around Europa. The quantities we take into account are C20, C22, the libration amplitude, the obliq- uity, the Love number k2 and its quality factor Q. For their dependence on the internal structure, see e.g. [2], [3], [4], [5], [6], [7] and [8]. ll these quantities induce perturbations (secular, long term and short period) of the orbital elements of the orbiter, thereby changing the spacecraft position and the relative radial velocity between the orbiter and a terrestrial observer (or Doppler signal). We calculate these perturbations by integration of Lagrange’s equa- tions in order to obtain an analytical expression for the Doppler signal (see [9] for a similar study for Mars). The effect of each parameter on the Doppler signal is determined for different initial orbital elements of the orbiter. To test the measurability, the effects are compared with the expected accuracy of the Doppler signal. [1] Anderson, J. D. et al. (1999) Science , 281, 2019– 2022. [2] Van Hoolst, T. et al. (2008) Icarus , 195, 386–399. [3] Van Hoolst, T. et al. (2009) Icarus , 200, 256–264. [4] Peale, S. J. et al. (1988) Mercury, University of Arizona Press , 461–493. [5] Bills, B. G. and Nimmo F. (2008) Icarus , 196, 293–297. [6] Wu, X. et al. (2001) Geophysical Research Let- ters , 28, 2245–2248. [7] Wahr, J. M. et al. (2006) JGR , 111, 12005–. [8] Lainey, V. (2005) PhD Thesis, Observatoire de Paris [9] Yseboodt, M. (2003) PhD Thesis, UC
On the coupling between magnetic field and nutation in a numerical integration approach,J.Geophys.Res.
No full textDe aardbeving en tsoenami van 26 december 2004 in de Indische Oceaan: 1. De aardbeving van 26 december 2004
No full textDe aardbeving en tsoenami van 26 december 2004 in de Indische Oceaan: 2. De tsoenami van 26 december 2004
No full textInfluence of triaxiality and second-order terms in flattenings on the rotation of terrestrial planets
No full textUnlike for the Earth, the equatorial flattening of Mars is important and almost of the same magnitude as the polar flattening. The classical semi-analytical model for the rotation of an ellipsoidal rotating planet with an elastic mantle and incompressible fluid core is therefore extended to incorporate the effects of the planet’s triaxiality. As triaxiality effects are nevertheless small, other second-order effects in the small parameters not related to triaxiality have also been taken into account. The absolute values of the frequencies of two rotational normal modes: (1) the free core nutation (FCN); and (2) the Chandler wobble (CW), are found to be smaller than the corresponding frequencies for a biaxial planet. The period change is larger for the CW than for the FCN, for which the triaxiality effect is comparable to the effect associated with the other second-order terms, and amounts to about 1 day for the CW of Mars
Slichter modes of large icy satellites
No full textBecause of the presence of an ocean below the ice shell of icy satellites such as Europa, Callisto, Ganymede and Titan the solid interior of these satellites can be displaced with respect to the ice shell, similarly to the translational oscillation of the inner core of the Earth called the Slichter modes of the Earth. We construct a set of interior structure models of Europa, Callisto, Ganymede and Titan satisfying the observed mass, radius and moment of inertia and study the properties of the Slichter mode for these models. The periods obtained range from a few hours to a few tens of hours depending mainly on the ocean thickness. Ganymede has two Slichter modes since it is thought to have a liquid outer core besides a global subsurface ocean. The second Slichter mode describes essentially the oscillation of the solid inner core inside the liquid outer core and its period is determined principally by the thickness of the outer core. We study the possible observation of these modes with a lander on the surface or a spacecraft in orbit about Europa, Callisto, Ganymede or Titan. We show that an impactor with a radius of at least a few kilometers to a few tens of kilometers could excite the Slichter modes to a level observable by a lander. Such impacts occur on average once in >30. My for Europa, once in >70. My for Callisto, once in >40. My for Ganymede and once in >0.4. Gy for Titan. Observation of the Slichter mode would allow constraining the thickness of the ocean. © 2013 Elsevier Inc
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