± 0.010 0.142[4] 78.3 ± 1.5 C 3.6 ± 0.10 10]

[Figure: Fig. 6. Residuals obtained by comparisons between INPOP08 and MEX tracking data (left hand side) and VEX (right hand side) observations. The small dark points represent residuals of observations which were used in the fit of INPOP08 and the big dark points represent residuals of observations not used in the fit. The large slope of MEX residuals may possibily be improved in the future with better determination of asteroid masses.]

6.2. Uncertainties by comparisons with other ephemerides
However, for all the other users, the comparison to observations is interesting only if they correspond to their specific use. In general, users prefer to have a more theoretical estimation such as the uncertainties in the barycentric positions and velocities of the Earth. To answer this question, we use comparisons between different ephemerides to estimate the level of variations induced by an improvement of modeling or adjustment (section 6.2).
Another way to estimate the uncertainties of planet orbit is to compare several ephemerides. By such comparisons, one estimates first the impact of the differences in dynamical modeling of each ephemeris and in adjustment to observations: the ephemerides could have been fitted over different sets of observations with different sets of weight and with different sets of parameters. Table 5 presents the maximum differences in barycentric positions and velocities between INPOP08 and INPOP06. Table 6 presents the corresponding maximum differences between INPOP08 and DE421. Two intervals of time are considered to estimate these differences: interval A from 1990 to 2010 and interval B from 1900 to 2050. Furthermore, plots of heliocentric differences in ecliptic longitudes obtained by comparisons between the same ephemerides are presented in figure 7. The use of Cassini normal points in DE421 and INPOP08 make the differences between the two ephemerides decrease significantly for the longitude of Saturn, as well as for the other outer planets.
6.1. Extrapolation tests
Two sets of observations of MEX and VEX were kept out from the fit procedure as test sample of INPOP08. These sets were obtained from April 2008 to September 2008. Differences in meters obtained by comparisons between the observed and INPOP08 distances can be found in figure 6. For Mars, the linear drift observed is in the order of error expected (about 20 meters over half a year) and is mainly due to asteroid modeling and adjustment.
For Venus, the distribution is noisier, but in good continuity with the postfit residuals obtained after the INPOP08 fit and presented in Figure 6. The biggest noticeable effect on these residuals is induced by the VEX solar conjunction that occured on June 9th 2008. This solar conjunction has introduced unmodeled noise into the doppler and ranging data of VEX during a period of few days (between the 06 to 11 June inclusive) during when the spacecraft tracking was stopped. The peak that can be noticed on Figure 6 is then mainly induced by this conjunction.
If one consider that these differences give a good estimation of their actual accuracies, then thanks to the Cassini data, we can see the improvement of the orbit at the epoch of these observations.
Limited improvements of the outer planet orbits will be possible by the addition of more accurate data in the fit, mainly tracking data of spacecraft orbiting or cruising one of these systems, such as the New Millenium mission. Important improvements will be obtained after having significant portion of orbit covered by accurate observations New sets of observations were used for the construction of INPOP08:

[Table: Table 5. Maximum differences between INPOP06 and INPOP08 estimated on interval A from 1990 to 2010 and on interval B from 1900 to 2050.
Barycentric Barycentric Positions (m) Velocities (m/d) Interval A B A B Mercury 3500 4600 260 280 Venus 1700 2500 37 41 EMB 760 4000 11 48 Mars 980 14000 9 140 Jupiter 240000 1300000 350 1900 Saturn 320000 560000 161 320 Uranus 1800000 1800000 290 410 Neptune 2400000 7500000 320 620 Pluto 7500000 140000000 1700 7200]