Normal fault earthquakes or graviquakes

Earthquakes are dissipation of energy throughout elastic waves. Canonically is the elastic energy accumulated during the interseismic period. However, in crustal extensional settings, gravity is the main energy source for hangingwall fault collapsing. Gravitational potential is about 100 times larger than the observed magnitude, far more than enough to explain the earthquake. Therefore, normal faults have a different mechanism of energy accumulation and dissipation (graviquakes) with respect to other tectonic settings (strike-slip and contractional), where elastic energy allows motion even against gravity. The bigger the involved volume, the larger is their magnitude. The steeper the normal fault, the larger is the vertical displacement and the larger is the seismic energy released. Normal faults activate preferentially at about 60° but they can be shallower in low friction rocks. In low static friction rocks, the fault may partly creep dissipating gravitational energy without releasing great amount of seismic energy. The maximum volume involved by graviquakes is smaller than the other tectonic settings, being the activated fault at most about three times the hypocentre depth, explaining their higher b-value and the lower magnitude of the largest recorded events. Having different phenomenology, graviquakes show peculiar precursor

Precise pose estimation of the NASA Mars 2020 Perseverance rover through a stereo-vision-based approach

Visual Odometry (VO) is a fundamental technique to enhance the navigation capabilities of planetary exploration rovers. By processing the images acquired during the motion, VO methods provide estimates of the relative position and attitude between navigation steps with the detection and tracking of two-dimensional (2D) image keypoints. This method allows one to mitigate trajectory inconsistencies associated with slippage conditions resulting from dead-reckoning techniques. We present here an independent analysis of the high-resolution stereo images of the NASA Mars 2020 Perseverance rover to retrieve its accurate localization on sols 65, 66, 72, and 120. The stereo pairs are processed by using a 3D-to-3D stereo-VO approach that is based on consolidated techniques and accounts for the main nonlinear optical effects characterizing real cameras. The algorithm is first validated through the analysis of rectified stereo images acquired by the NASA Mars Exploration Rover Opportunity, and then applied to the determination of Perseverance's path. The results suggest that our reconstructed path is consistent with the telemetered trajectory, which was directly retrieved onboard the rover's system. The estimated pose is in full agreement with the archived rover's position and attitude after short navigation steps. Significant differences (~10–30 cm) between our reconstructed and telemetered trajectories are observed when Perseverance traveled distances larger than 1 m between the acquisition of stereo pairs

The ν\nu-cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering

We discuss a small-scale experiment, called $\nu$-cleus, for the first detection of coherent neutrino-nucleus scattering by probing nuclear-recoil energies down to the 10 eV-regime. The detector consists of low-threshold CaWO$_4$ and Al$_2$O$_3$ calorimeter arrays with a total mass of about 10 g and several cryogenic veto detectors operated at millikelvin temperatures. Realizing a fiducial volume and a multi-element target, the detector enables active discrimination of $\gamma$, neutron and surface backgrounds. A first prototype Al$_2$O$_3$ device, operated above ground in a setup without shielding, has achieved an energy threshold of ${\sim20}$ eV and further improvements are in reach. A sensitivity study for the detection of coherent neutrino scattering at nuclear power plants shows a unique discovery potential (5$\sigma$) within a measuring time of ${\lesssim2}$ weeks. Furthermore, a site at a thermal research reactor and the use of a radioactive neutrino source are investigated. With this technology, real-time monitoring of nuclear power plants is feasible.Comment: 14 pages, 19 figure

Lunar Surface exploration based on LCNS orbiters and Onboard Sensor observables

Lunar exploration is a strategic priority to develop and experiment technologies that will pave the way for the future missions to Mars and to other celestial bodies of the Solar System. Robots are expected to prepare the return of humans to the Moon by surveying landing sites, demonstrating in situ resource utilization (ISRU), and expanding our access capabilities to difficult areas, i.e., craters and caves. Succeeding in these challenging tasks requires reliable and efficient navigation and communication capabilities. Therefore, space agencies are encouraging the development of a Lunar Communication and Navigation Service (LCNS) to efficiently support lunar assets. A dedicated LCNS infrastructure would lead to unprecedent advantages in future missions by enabling a constant contact with Earth, even in case of Direct To Earth (DTE) link unavailability, e.g., on the far side of the Moon. To fulfil critical tasks, such as obstacle avoidance, instrument manoeuvring and reaching a precise location on the map, rover near real time positioning is a key requirement. Thus, in our work we investigate a method based on the Extended Kalman Filter (EKF) that implements a multi modal sensor fusion approach to estimate the rover's position and velocity by using observables collected by onboard sensors or provided by a LCNS constellation. We focus on a realistic mission scenario in the Moon's south polar region that includes a robotic vehicle hosting onboard sensors to estimate the travelled distances (Wheel Odometry, WO) and the heading variation (Inertial Measurement Unit, IMU). Furthermore, the LCNS orbiters are supposed to broadcast one-way radio signals that the rover user terminal can detect and exploit, providing GNSS-like functionalities. The rover's localization is accomplished through dead-reckoning during LCNS visibility gaps, by using IMU and WO data and accurate Digital Elevation Models (DEMs) of the lunar surface. Whenever pseudorange and pseudorange rate data are acquired by the rover LCNS terminal, these measurements are processed by the navigation filter in combination with IMU and WO datasets, while optimizing the position, velocity and timing (PVT) computation in terms of integrity, accuracy, and convergence time. The proposed method copes with highly varying LCNS visibility conditions and would significantly improve rover's navigation on the Moon's surface in regions where DTE is not achievable. Moreover, our results confirm that the LCNS would be a valuable source of information to be exploited in combination with onboard sensors to improve the accuracy of the reconstructed rover's traverse