5.1.1. Contribution of VEX data
The impact of VEX observations on the INPOP08 adjust-
ment is very important. As one can see in Figure 3 and
table 1, INPOP08 provides a much more accurate Venus
orbit thanks to the VEX input data. This improvement is
mainly induced by the fit of planet initial conditions and
also by the improvement of the modelisation of the aster-
oid perturbations on the inner planets. A mean dispersion by ESA before the MEX launch.

[Figure: Fig. 3. VEX 1-way residuals with the new INPOP08 fitted to VEX and MEX data (dark curve) and INPOP06 not fitted on VEX observations (light curve). The solar conjonction is clearly identified with the peak of residuals in october 2006.]

Even if a great improvement can be noticed on Figure 4, signals still remain in INPOP08 residuals due to a still possible lack in asteroid mass determinations but also to systematics induced by solar conjunction gaps in the data sets.
masses obtained after radar imaging (Michalak 2000) and masses fitted during the global adjustments of planetary ephemerides marked as black crosses. The close-encounter method was used a lot in the 90s but due to the difficulty of the method (accurate observations of the perturbed objects to obtain very accurate estimation of its orbit and to survey the orbit during the close-encounters), the effort was not maintained during the last decade. On the other hand, the evolution of planetary ephemerides gives very stable estimations for the largest asteroids with uncertainties smaller than the close-encounters determinations. In 2008, (Baer and Chesley) published values established on the basis of several encounters and obtained values of masses for Ceres, Pallas and Vesta very close to the ones obtained by the planetary ephemerides. For Ceres and Vesta, the uncertainties of the close-ecounters determinations are at the same level of accuracy as planetary ephemerides ones. INPOP08 gives original values offset from the previous estimations but at the limit of the error bars. In table 3, are given the masses of the 28 asteroid, other than the 5 bigs given in table 2, fitted individually in INPOP08. The estimated mass values are put in the table as their mean impact on the Earth-Mars distances (estimated over 20 years) decreases. For some of them, the INPOP08 masses agree in the limit of 30 % with values estimated previously either by close-encounters methods (as for (16) Psyche, (52) Europa, (88) Thisbe, (8) Flora, (15) Eunomia, (18) Melpomene (19) Fortuna, and (21) Lutecia) or by adjustment of planetary ephemerides (as for (41) Daphne, (29) Amphitrite, (409) Aspasia, (704)
In Table 2 and 3, asteroid masses fitted in INPOP08 are compared to other published masses as well as values for taxonomic densities and physical characteristics of the asteroid ring. In the case of INPOP08, the ring mass and distance were not fitted during the global adjustment but during the construction of the ring (see section 3). Due to the direct correlation between the mass of the ring and its distance to the Sun, we decided to fix arbitrarily the distance at 3.14 AU. If this distance is chosen at 2.8 AU, the mass of the ring is estimated to be Mring = 0.3 ± 0.1 × 10−10M�which is comparable with the GM estimated by DE414 and very close to the one given by INPOP06. In table 2, the taxonomic densities estimated by INPOP08 stay of the same order as those estimated by DE414 or DE421 and the values of masses estimated for the 5 biggest asteroids are also in good agreement with those published previously. Figure 5 depicts the same conclusion. Indeed, on figure 5, the values estimated since 1991 (Baer and Chesley 2008) of GMs of Ceres, Pallas and Vesta are plotted as well as the values provided by INPOP06, DE414, DE421 and INPOP08 which correspond to the four last points dated in 2008 and 2009. On this graph, are represented (using darked circles) asteroid masses estimated by close-encounters (see for instance Baer and Chesley 2008, Hilton 1999), asteroid and try to estimate its mass only on that arc.