Solar system

Abstract:

Barotropic instability represents a class of instabilities, usually of parallel shear flows, for which gravity and buoyancy play a negligible role, at least in their energetics. It is not restricted to purely barotropic fluids (for which ρ = ρ(p), where ρ is density and p is pressure) but can also apply to flows which are stratified and exhibit vertical shear, often leading to instabilities with mixed barotropic and baroclinic characteristics. The primary attribute of barotropic instability is usually taken to be the dominance of energy exchanges in which the kinetic energy of a perturbation grows principally at the expense of the kinetic energy of the basic state. Here we present an introduction to the basic mechanisms involved and the factors that determine the necessary and/or sufficient conditions for instability. Several examples are presented and the occurrence and subsequent nonlinear evolution of the instability is illustrated with reference to both laboratory experiments and observations in the atmospheres and oceans of the Earth and other planets in the Solar System.

Abstract:

The Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has detected as many as 1,125 plasma depletion events (PDEs) in the Martian ionosphere from October 2014 to May 2021. PDEs, characterized by significantly reduced plasma density, elevated electron temperatures, and increased electrostatic fluctuations, remain poorly understood in terms of their formation and spatiotemporal characteristics. This study combines MAVEN data with concurrent observations from Mars Express (MEX) to investigate these aspects. The analysis of PDE recurrence rates across subsequent MAVEN orbits reveals 80 recurring events. These events are formed at the same locations within 18–30 hr. Additionally, we identified two conjugate PDEs observed by both MAVEN and MEX. These observations suggest that PDEs can extend spatially up to 750 km and last for a couple of hours. Our findings suggest that PDEs are large-scale and possibly recurring phenomena, potentially important for ion loss, and that understanding them is important for accurately characterizing the Martian ionosphere.

Abstract:

We needed to evaluate available orbital data of NASA’s Volatiles Investigating Polar Exploration Rover (VIPER) mission area in order to derive a variety of maps to help the science team identify scientifically interesting places for the rover to visit and to provide scientific context for our mission. Some of these maps also fulfilled engineering and mission design needs to enable safe and efficient landing and roving. We incorporated data from the Lunar Reconnaissance Orbiter Camera, the Lunar Orbital Laser Altimeter, the Mini-RF instrument, the Chandrayaan-2 Orbital High Resolution Camera, the Korean Pathfinder Lunar Orbiter’s Shadowcam, the Kaguya Spectral Profiler and Multiband Imager, and the Chandrayaan-1 Moon Mineralogy Mapper. We used a variety of techniques to build these maps, including stereogrammetry, shape-from-shading, ice stability depth and surface temperature calculations, and the horizon method for solar illumination and direct-to-Earth communications maps. Altogether, these maps allowed us to survey for boulders, evaluate features in permanently shadowed regions that VIPER might explore, provide mineralogic context for what VIPER’s instruments may learn, estimate the ages and radar properties of craters in the VIPER mission area, and evaluate the potential for gravity traverses with the rover. These data and techniques provided a rich set of information from which both the VIPER science team and engineering teams were able to draw in order to plan a safe landing and to plan a VIPER surface mission that will be both scientifically valuable and robust from an operational perspective.

Abstract:

Plain Language Summary: Earth absorbs energy emitted by the Sun, radiating some of that as heat back into space. The energy exchange between Earth and space drives weather and climate. Scientists measure and track this energy using satellite instruments that can identify which parts of Earth's surface and atmosphere emit specific portions of the overall heat radiated into space. But these instruments are complicated and expensive, and until now, no one has built a sensor that can look at and separate all of Earth's heat emissions in a systematic way. The Polar Radiant Energy in the Far‐InfraRed Experiment (PREFIRE) has developed a novel instrument that combines simple, miniaturized heat sensors with specially shaped optics and microelectronics to provide such measurements to further our understanding of the planet's weather and climate. Furthermore, implementation of the sensors has been done within a cost‐capped mission profile that encourages development of a sustainable sensor system for Earth monitoring. This manuscript describes the instrument design, including its components and their characteristics, the system and its functionality, its trade‐offs, cost limitations, and testing and performance information. PREFIRE began operating two of these instruments in space in 2024, in order to start quantifying the heat exchange processes in Earth's polar regions.

Abstract:

We present a new method, based on a joint application of a principal component analysis (PCA) and Gaussian mixture models (GMM), to automatically find similar groups of spectra in a collection. We applied the method (condensed in the public code chopper.py ) to archival Jupiter spectral data in the 2–5 µm range collected by NASA Juno/JIRAM in its first perijove passage (August 2016) and to mosaics of the great red spot (GRS) acquired by JWST/NIRSpec (July 2022). Using JIRAM data analyzed in previous work, we show that using a PCA+GMM clustering can increase the efficiency of the retrieval stage without any loss of accuracy in terms of the retrieved parameters. We show that a PCA+GMM approach is able to automatically identify spectra of known regions of interest (e.g., belts, zones, GRS) belonging to different clusters. The application of the method to the NIRSpec data leads to detection of substructures inside the GRS, which appears to be composed of an outer halo characterized by low reflectivity and an inner brighter main oval. By applying these techniques to JIRAM data, we were able to identify the same substructure. We remark that these new structures have not been seen before at visible wavelengths. In both cases, the spectra belonging to the inner oval have solar and thermal signals comparable to those belonging to the halo, but they present broadened 2.73 µm solar-reflected peaks. Performing forward simulations with the NEMESIS radiative transfer suite, we propose that the broadening may be caused by differences in the vertical extension of the main cloud layer. This finding is consistent with recent 3D fluid dynamics simulations.