Solar system

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.

Abstract:

A planet's interior is a time capsule, preserving clues to its early history. We report the discovery of kilometer-scale heterogeneities throughout Mars' mantle, detected seismically through pronounced wavefront distortion of energy arriving from deeply probing marsquakes. These heterogeneities, likely remnants of the planet's formation, imply a mantle that has undergone limited mixing driven by sluggish convection. Their size and survival constrain Mars' poorly known mantle rheology, indicating a high viscosity of 10^21.3 to 10^21.9 pascal-seconds and low temperature dependence, with an effective activation energy of 70 to 90 kilojoules per mole, suggesting a mantle deforming by dislocation creep. The limited mixing, coupled with ubiquitous, scale-invariant heterogeneities, reflects a highly disordered mantle, characteristic of the more primitive interior evolution of a single-plate planet, contrasting sharply with the tectonically active Earth.

Abstract:

The presence of cryovolcanic activity in the form of geyser-like plumes at Jupiter’s moon Europa is a much-debated topic. As an active plume could allow direct sampling by a passing spacecraft of a potentially habitable interior environment, the detection and analysis of ongoing plume activity would be of the highest scientific value. In the past decade, several studies have interpreted different remote and in situ observations as providing evidence for large gaseous plumes at different locations on Europa. However, definitive proof is elusive, and visible imaging data taken during spacecraft flybys do not reveal clear indications of ongoing activity. After arrival at Jupiter in 2030, the NASA Europa Clipper spacecraft will systematically search for and constrain plume activity at Europa utilizing a variety of investigations and methods during, before, and after close flybys. Given the lack of a confirmed plume detection to date, the Europa Clipper science team has adopted a global plume search strategy, not focusing on any specific geographical area or any specific type of observation. This global search strategy assigns enhanced value to data obtained early in the mission, which allows time for further observations and characterization of any observed plume at later times. Here we describe the current state of knowledge on plume activity, the Europa Clipper search strategy, and the role of various instruments on the Europa Clipper payload in this search.

Abstract:

Activity in small bodies, defined here as the episodic or continuous release of material, was long thought to be exclusively a behavior of comets, but it has since been discovered in some centaurs, main-belt asteroids, and near-Earth asteroids. To date, however, no activity has been discovered on Jovian trojan asteroids, the target of NASA’s Lucy Discovery Program mission. Although Lucy was originally conceived without studies of or searches for trojan activity, it was realized in 2016–2017 that the spacecraft and scientific payload aboard Lucy could provide unique and meaningful constraints or detections on activity in these trojans. Here we describe how the Lucy mission will search for such activity using (i) its terminal tracking navigation camera to search for wide-field coma scattered light, (ii) its Lucy Long Range Reconnaissance Imager narrow-angle camera to also search for scattered light from any coma or jets, and (iii) its Multispectral Visible Imaging Camera imager to search for CN emission (a common activity tracer species in comets). Sensitivity estimates for each of those measurements are discussed below.

Abstract:

Research into compositions of small bodies and planetary surfaces, such as asteroids, is key to understanding the origin of water and organics on Earth [1], as well as placing constraints on planetary dynamics and migration models [2] that can help understand how planetary systems around other stars may form and evolve. Compositional estimates can be found with thermal infrared (TIR; 5-25μm) spectroscopy, as the TIR region is rich in diagnostic information and can be used in remote sensing observations and laboratory measurements. However, TIR spectra of the same material may appear differently depending on several factors, such as particle size, surface roughness, porosity etc. This work quantifies the changes in spectral morphology (i.e., shapes and depths of spectral features) as particle size transitions from fine (90%), at several size fractions, aimed to be