10 research outputs found
Use of MESSENGER radioscience data to improve planetary ephemeris and to test general relativity
The current knowledge of Mercury orbit has mainly been gained by direct radar
ranging obtained from the 60s to 1998 and by five Mercury flybys made by
Mariner 10 in the 70s, and MESSENGER made in 2008 and 2009. On March 18, 2011,
MESSENGER became the first spacecraft to orbit Mercury. The radioscience
observations acquired during the orbital phase of MESSENGER drastically
improved our knowledge of the orbit of Mercury. An accurate MESSENGER orbit is
obtained by fitting one-and-half years of tracking data using GINS orbit
determination software. The systematic error in the Earth-Mercury geometric
positions, also called range bias, obtained from GINS are then used to fit the
INPOP dynamical modeling of the planet motions. An improved ephemeris of the
planets is then obtained, INPOP13a, and used to perform general relativity
tests of PPN-formalism. Our estimations of PPN parameters (beta and gamma?) are
more stringent than previous results.Comment: Accepted by A&
Viscosity contrasts in the Venus mantle from tidal deformations
The tidal deformations of a planet are often considered as markers of its
inner structure. In this work, we use the tide excitations induced by the Sun
on Venus for deciphering the nature of its internal layers. In using a Monte
Carlo Random Exploration of the space of parameters describing the thickness,
density and viscosity of 4 or 5 layer profiles, we were able to select models
that can reproduce the observed mass, total moment of inertia, Love
number and expected quality factor . Each model is assumed to have
homogeneous layers with constant density, viscosity and rigidity. These models
show significant contrasts in the viscosity between the upper mantle and the
lower mantle. They also rather favor a S-free core and a slightly hotter lower
mantle consistent with previous expectations.Comment: Accepted for publication in Planetary and Space Science
Short Report of IVS Working Group 5 (WG5) on Space Science Applications - An IVS Perspective
No abstract availabl
Observational constraint on the radius and oblateness of the lunar core-mantle boundary
International audienceLunar laser ranging (LLR) data and Apollo seismic data analyses, revealed independent evidence for the presence of a fluid lunar core. However, the size of the lunar fluid core remained uncertain by km (encompassing two contrasting 2011 Apollo seismic data analyses). Here we show that a new description of the lunar interior's dynamical model provides a determination of the radius and geometry of the lunar core-mantle boundary (CMB) from the LLR observations. We compare the present-day lunar core oblateness obtained from LLR analysis with the expected hydrostatic model values, over a range of previously expected CMB radii. The findings suggest a core oblateness () that satisfies the assumption of hydrostatic equilibrium over a tight range of lunar CMB radii ( km). Our estimates of a presently-relaxed lunar CMB translates to a core mass fraction in the range of with a present-day Free Core Nutation (FCN) within years
New constraints on the Kuiper belt mass and P9 location from INPOP19a planetary ephemerides
HISTORICAL REFLECTIONS ON THE WORK OF COMMISSION 4
International audienceCommission 4 was among the first set of commissions formed within the IAU at its founding in 1919. (Commissions were originally called ``Standing Committees.'') During its 96 years of service to the IAU and astronomical community in general, the commission has been fortunate to have been led by many distinguished scientists - see the list of presidents below