The gravity fields of celestial bodies that possess an atmosphere are periodically perturbed by the redistribution of fluid mass associated with atmospheric dynamics. A component of this perturbation is due to the gravitational response of the body to the deformation of its surface induced by the atmospheric pressure loading. The magnitude of this effect depends on the relation between the loading and the response in terms of geopotential variations measured by the load Love numbers. In this work, we simulate and analyze the gravity field generated by the atmospheres of Venus and Mars by accounting for different models of their internal structure. By precisely characterizing the phenomena that drive the mass transportation in the atmosphere through general circulation models, we determine the effect of the interior structure on the response to the atmospheric loading. An accurate estimation of the time-varying gravity field, which measures the atmospheric contribution, may provide significant constraints on the interior structure through the measurement of the load Love numbers. A combined determination of tidal and load Love numbers would enhance our knowledge of the interior of planetary bodies, providing further geophysical constraints in the inversion of internal structure models.
Space robotic systems have been playing a crucial role in planetary exploration missions, expanding our access to harsh and hostile environments in the Solar System. Rovers' activities are still mainly controlled through ground operations, and our goal is to develop autonomous systems for navigation and path planning. The position estimates obtained by processing Wheel Odometry (WO) data induce significant errors because of wheels' loss of traction that is caused by, for example, high-slippage terrains (e.g., sandy-loose soils, steep slopes). Our work is focused on the implementation of a localization software based on Visual Odometry (VO). This is a technique developed for the estimation of rovers' position and attitude by using stereo images captured during the vehicle's motion. To determine the attainable accuracy of our software, we carried out a set of numerical simulations through a digitally-reproduced Martian-like environment. The results show that the algorithm allows reconstructing the rover's trajectory with higher accuracies compared to the localization system requirements of the NASA Mars Exploration Rovers (i.e., 10% error over a 100-m traverse [1]).
A radio occultation experiment consists in the analysis of the perturbations induced by the atmosphere on an electromagnetic signal propagating through it. The most relevant phenomena that affect a radio signal passing through a medium are refraction and absorption. The bending effects on the signal associated with refraction are related to the refractive index of the atmosphere (i.e., its real part), which in turn is linked to the atmospheric mass density, pressure, and temperature. Refraction causes a Doppler frequency shift of the signal traversing the atmosphere. A time series of frequency Doppler shifts is processed to identify the bending effects and, therefore, the atmospheric thermodynamic profiles, that is, a series of values obtained as a function of the radial distance from the center of the planet.Several methodologies have been developed to process radio occultation data. An approach is based on ray-tracing algorithms, and it is well suited for oblate refractive environments, such as Jupiter (Lindal et al., 1981), Saturn (Schinder et al., 2015), and Neptune (Lindal, 1992). Radio occultations of terrestrial planets and icy moons of the Solar System have been processed under the assumption of spherical symmetry of their atmospheres. Fjeldbo et al. (1971) proposed this method to obtain a simplified geometry of the Abstract Among the techniques for atmospheric sounding, radio occultation enables an in depth investigation of vertical profiles from the ionosphere to the troposphere by measuring the radio frequency signal associated to the propagation medium. A precise characterization of the atmospheric layers requires a thorough processing of the raw radio tracking data to estimate the thermodynamic properties of the atmosphere and their related uncertainties. In this work, we present a method to retrieve refractivity, density, pressure, and temperature profiles with the associated uncertainties by analyzing a set of raw radio tracking data occulted by the atmosphere. This technique is also well suited to process two-way Doppler measurements that are not acquired during dedicated occultation campaigns. The NASA mission Mars Reconnaissance Orbiter (MRO) provided a significant amount of radio occultation data that were not planned for atmospheric sounding, but were caused by the spacecraft orbit geometry. Our analysis of one of these occultation profiles with the proposed method allows indicating that MRO occultation datasets provide crucial information regarding Mars' troposphere that can be used as input of general circulation models.Plain Language Summary A solid technique to investigate the structure of a celestial body atmosphere is based on the analysis of the signals induced by the properties of this medium on the spacecraft radio links that pass through the atmosphere during communications with the Earth. A thorough study of these measurements, that is, radio occultation, allows estimating the vertical profiles of atmospheric density, pressure, and temperature. We present here a method to retrieve t...
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