Abstract
Aims: Several scientific landers and rovers have reached the Martian surface since the 1970s. Communication between the asset (i.e., lander or rover) and Mars orbiters or Earth antennas uses radio signals in UHF to X-band frequencies passing through the Mars’ ionosphere. It is consequently necessary to take into account electron density variation in the Mars’ ionosphere to correct the refraction of the signal transmitted. Methods: We developed a new empirical model of the Mars’ ionosphere called MoMo. It is based on the large database of Total Electron Content (TEC) derived from the subsurface mode of the Mars Express MARSIS radar. The model provides vertical TEC as a function of solar zenith angle, solar activity, solar longitude and location. For validation, the model is compared with Mars Express radio occultation data as well as with the numerical model IPIM (IRAP Plasmasphere-Ionosphere Model). Results: We discussed the output of the model in terms of climatology behaviour of the Mars’ ionosphere. The output of MoMo is then uses to quantify the impact of the Martian ionosphere for radio-science experiments. From our results, the effect is of the order of 10−3 mm s−1 in Doppler observables especially around sunrise and sunset. Consequently, this new model could be used to support the data analysis of any radio-science experiment and especially for present InSight RISE and futur ExoMars LARA instruments aiming at better understand the deep-interior of Mars.
Highlights
Radio-science experiments are used to obtain motions of spacecraft or asset around or on planets or moons in space
Where ch(Xp, Solar Zenith Angle (SZA)) is the function given in equation (2), a1 and a2 coefficients are parameters estimated to fit the observations by minimizing the squared differences between the modelled and observed vertical TEC (vTEC) from MARSIS data in a least-square sense
The mean of the differences in the North is 0.00 ± 0.04 TECu, while the differences in the South are 0.03 ± 0.06 TECu. This could be due to more intense ionospheric variability in the South not well represented in model of Mars’ ionosphere (MoMo) which aims at representing the climatology of the vTEC
Summary
Radio-science experiments are used to obtain motions of spacecraft or asset (e.g., lander and rover) around or on planets or moons in space. The impact of a liquid core on Martian Orientation Parameters is lower than 0.004 mm sÀ1 in X-band (Yseboodt et al, 2017) and could be detected from data time-series To reach this accuracy, the ionospheres of Mars and Earth as well as the interplanetary plasma contributions need to be corrected for along the line of sight. Landers have usually only one frequency disabling the correction for these effects This is the case for the radio-science experiments RISE and Lara which use only one S-band frequency. The aim of the present paper is to provide a new model of the Mars’ ionosphere with few coefficients, simple to use but taking into account for areophysical considerations (i.e., absorption of the solar EUV in a terrestrial atmosphere, seasons, hemispheric dichotomies) and adapted to correct data for any experiment using radio signals. The second section describes the climatology behaviour of the Mars’ ionosphere using our model, and provides some applications to radio-science experiments
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