A ring as a model of the main belt in planetary ephemerides

We assess the ability of a solid ring to model a global perturbation induced by several thousands of main-belt asteroids. The ring is first studied in an analytical framework that provides an estimate of all the ring's parameters excepting mass. In the second part, numerically estimated perturbations on the Earth-Mars, Earth-Venus, and Earth-Mercury distances induced by various subsets of the main-belt population are compared with perturbations induced by a ring. To account for large uncertainties in the asteroid masses, we obtain results from Monte Carlo experiments based on asteroid masses randomly generated according to available data and the statistical asteroid model. The radius of the ring is analytically estimated at 2.8 AU. A systematic comparison of the ring with subsets of the main belt shows that, after removing the 300 most perturbing asteroids, the total main-belt perturbation of the Earth-Mars distance reaches on average 246 m on the 1969-2010 time interval. A ring with appropriate mass is able to reduce this effect to 38 m. We show that, by removing from the main belt ~240 asteroids that are not necessarily the most perturbing ones, the corresponding total perturbation reaches on average 472 m, but the ring is able to reduce it down to a few meters, thus accounting for more than 99% of the total effect.Comment: 18 pages, accepted in A&

Gravity tests with INPOP planetary ephemerides

In this paper, we present several gravity tests made in using the last INPOP08 planetary ephemerides. We first propose two methods to estimate the PPN parameter $\beta$ and its correlated value, the Sun J2 and we discuss the correlation between the Sun J2 and the mass of the asteroid ring. We estimate possible advance in the planet perihelia. In the end we show that no constant acceleration larger than 1/4 the Pioneer anomaly can affect the planets of our solar system.Comment: 11 pages. submitted to proceedings of IAU symposium 264 "Relativity in Fundamental Astronomy: Dynamics, Reference Frames and Data analysis

Constraints on the location of a possible 9th planet derived from the Cassini data

To explain the unusual distribution of Kuiper Belt objects, several authors have advocated the existence of a super-Earth planet in the outer solar system. It has recently been proposed that a 10 M$_{\oplus}$ object with an orbit of 700 AU semi major axis and 0.6 eccentricity can explain the observed distribution of Kuiper Belt objects around Sedna. Here we use the INPOP planetary ephemerides model as a sensor for testing for an additional body in the solar system. We test the possibility of adding the proposed planet without increasing the residuals of the planetary ephemerides, fitted over the whole INPOP planetary data sample. We demonstrate that the presence of such an object is not compatible with the most sensitive data set, the Cassini radio ranging data, if its true anomaly is in the intervals $[-130^\circ:-100^\circ]$ or $[-65^\circ : 85^\circ]$. Moreover, we find that the addition of this object can reduce the Cassini residuals, with a most probable position given by a true anomaly $v = {117.8^\circ}^{ + 11^\circ}_{ - 10^\circ}$.Comment: Accepted for publication in A&A; 4 pages, 6 figure

Tests of General relativity with planetary orbits and Monte Carlo simulations

Based on the new developped planetary ephemerides INPOP13c, determinations of acceptable intervals of General Relativity violation in considering simultaneously the PPN parameters $\beta$, PPN $\gamma$, the flattening of the sun $J_{2}^\odot$ and time variation of the gravitational mass of the sun $\mu$ are obtained in using Monte Carlo simulation coupled with basic genetic algorithm. Possible time variations of the gravitational constant G are also deduced. Discussions are lead about the better choice of indicators for the goodness-of-fit for each run and limits consistent with general relativity are obtained simultaneously.Comment: submitte

INPOP new release: INPOP13b

Based on the use of MESSENGER radiotracking data in the construction of new Mercury ephemerides (Verma et al. 2014) a new planetary ephemerides INPOP13b was built including Mercury improvements but also improvements on the Mars orbit and on the tie of INPOP planetary ephemerides to ICRF in general.Comment: INPOP sources available http://www.imcce.fr/inpo

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&

Electron density distribution and solar plasma correction of radio signals using MGS, MEX and VEX spacecraft navigation data and its application to planetary ephemerides

The Mars Global Surveyor (MGS), Mars Express (MEX), and Venus Express (VEX) experienced several superior solar conjunctions. These conjunctions cause severe degradations of radio signals when the line of sight between the Earth and the spacecraft passes near to the solar corona region. The primary objective of this work is to deduce a solar corona model from the spacecraft navigation data acquired at the time of solar conjunctions and to estimate its average electron density. The corrected or improved data are then used to fit the dynamical modeling of the planet motions, called planetary ephemerides. We analyzed the radio science raw data of the MGS spacecraft using the orbit determination software GINS. The range bias, obtained from GINS and provided by ESA for MEX and VEX, are then used to derive the electron density profile. These profiles are obtained for different intervals of solar distances: from 12Rs to 215Rs for MGS, 6Rs to 152Rs for MEX, and form 12Rs to 154Rs for VEX. They are acquired for each spacecraft individually, for ingress and egress phases separately and both phases together, for different types of solar winds (fast, slow), and for solar activity phases (minimum, maximum). We compared our results with the previous estimations that were based on in situ measurements, and on solar type III radio and radio science studies made at different phases of solar activity and at different solar wind states. Our results are consistent with estimations obtained by these different methods. Moreover, fitting the planetary ephemerides including complementary data that were corrected for the solar corona perturbations, noticeably improves the extrapolation capability of the planetary ephemerides and the estimation of the asteroids masses.Comment: Accepted for publication in A&