Sazuna/UAT_keywords huggingface dataset:
Lucy Mission to the Trojan Asteroids: Science Goals. The Lucy Mission is a NASA Discovery-class mission to send a highly capable and robust spacecraft to investigate seven primitive bodies near both the L4 and L5 Lagrange points with Jupiter: the Jupiter Trojan asteroids. These planetesimals from the outer planetary system have been preserved since early in solar system history. The Lucy mission will fly by and extensively study a diverse selection of Trojan asteroids, including all the recognized taxonomic classes, a collisional family member, and a near equal-mass binary. It will visit objects with diameters ranging from roughly 1 km to 100 km. The payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. Additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras will supplement imaging during closest approach and the telecommunication subsystem will be used to measure the mass of the Trojans. The science goals are derived from the 2013 Planetary Decadal Survey and include determining the surface composition, assessing the geology, determining the bulk properties, and searching for satellites and rings.

Keywords: Flyby missions, Jupiter trojans
Lucy Mission to the Trojan Asteroids: Instrumentation and Encounter Concept of Operations. The Lucy Mission accomplishes its science during a series of five flyby encounters with seven Trojan asteroid targets. This mission architecture drives a concept of operations design that maximizes science return, provides redundancy in observations where possible, features autonomous fault protection, and utilizes onboard target tracking near closest approach. These design considerations reduce risk during the relatively short time-critical periods when science data is collected. The payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. The mission design allows for concurrent observations of all instruments. Additionally, two spacecraft subsystems will also contribute to the science investigations: the Terminal Tracking Cameras will obtain wide field-of-view imaging near closest approach to determine the shape of each of the Trojan targets and the telecommunication subsystem will carry out Doppler tracking of the spacecraft to determine the mass of each of the Trojan targets.

Keywords: Space vehicles, Flyby missions, Jupiter trojans
The Double Asteroid Redirection Test (DART): Planetary Defense Investigations and Requirements. The Double Asteroid Redirection Test (DART) is a Planetary Defense mission, designed to demonstrate the kinetic impactor technique on (65803) Didymos I Dimorphos, the secondary of the (65803) Didymos system. DART has four level 1 requirements to meet in order to declare mission success: (1) impact Dimorphos between 2022 September 25 and October 2, (2) cause at least a 73 s change in its binary orbit period via the impact, (3) measure the change in binary period to an uncertainty of 7.3 s or less, and (4) measure the momentum transfer efficiency (β) of the impact and characterize the resulting effects of the impact. The data necessary to achieve these requirements will be obtained and analyzed by the DART Investigation Team. We discuss the rationales for the data to be gathered, the analyses to be undertaken, and how mission success will be achieved.

Keywords: Impact phenomena, Asteroid satellites, Near-Earth objects, Asteroids
UMaMI: A New Frontiers-style Mission Concept to Explore the Uranian System. With the public and scientific community's growing interest in ocean worlds, the icy moons of Uranus offer an ideal opportunity to explore a native ice giant satellite system. Although it is uncertain whether any of the Uranian moons currently host subsurface oceans, there is tantalizing evidence-including geologically young surface features and volatiles that are not stable-that this could be the case, making these objects possible ocean worlds in their own right. Determining whether subsurface oceans are present in the interiors of these moons would increase our understanding of the conditions under which subsurface oceans are formed and maintained over the history of the solar system. The presence and stability of a subsurface ocean in the interiors of any icy body is key to identifying its potential as a habitable environment. In this work, we describe a midsize (New Frontiers class) mission concept: the Uranian Magnetosphere and Moons Investigator. The magnetosphere and moons are tightly coupled parts of the Uranian system, complementary to study, and best analyzed together in order to investigate the Uranian moons as potential ocean worlds. Additionally, this mission concept includes study of Uranus's unique rings and magnetosphere-solar wind interaction. With a future, more detailed trade study, there also could be opportunities for studies of Uranus itself.

Keywords: Uranus, Planetary science, Uranian satellites
Detection of Large Exospheric Enhancements at Mercury due to Meteoroid Impacts. The Ultraviolet and Visible Spectrometer (UVVS) on the MESSENGER spacecraft observed three large transient events in Mercury's nightside "tail" in which the exospheric brightness increased by an order of magnitude. Meteoroid impacts are the best explanation given that the events are brief, can be simulated with instantaneous injections of vapor, and were not associated with unusual solar wind conditions. Data-model comparisons suggest that the impactors are 10-20 cm in diameter and produce vapor temperatures of ~104 K, much warmer than usually assumed for impact vapor. We estimate the impact frequency to be on the order of once per Earth day for meteoroids 10 cm diameter and larger, consistent with a pre-MESSENGER prediction. UVVS observed three atomic species during one event: sodium, magnesium, and calcium. Na and Mg brightened simultaneously, and their modeled ejection ratio roughly matches Mercury's surface abundance. Ca showed no sign of an enhancement, consistent with earlier predictions that Ca in impact vapor is bound in a molecule that is undetectable to UVVS. This event provides an unprecedented opportunity to see three species respond (or not) to a single source and has implications for our understanding of Mercury's exosphere.

Keywords: Impact phenomena, Meteoroids, Exosphere, Space weather, Solar-planetary interactions, Mercury (planet)
Nondetection of Water-ice Grains in the Coma of Comet 46P/Wirtanen and Implications for Hyperactivity. Hyperactive comets have high water production rates, with inferred sublimation areas of order the surface area of the nucleus. Comets 46P/Wirtanen and 103P/Hartley 2 are two examples of this cometary class. Based on observations of comet Hartley 2 by the Deep Impact spacecraft, hyperactivity appears to be caused by the ejection of water-ice grains and/or water-ice-rich chunks of nucleus into the coma. These materials increase the sublimating surface area and yield high water production rates. The historic close approach of comet Wirtanen to Earth in 2018 afforded an opportunity to test Hartley 2-style hyperactivity in a second Jupiter-family comet. We present high spatial resolution, near-infrared spectroscopy of the inner coma of Wirtanen. No evidence for the 1.5 or 2.0 μm water-ice absorption bands is found in six 0.8-2.5 μm spectra taken around perihelion and closest approach to Earth. In addition, the strong 3.0 μm water-ice absorption band is absent in a 2.0-5.3 μm spectrum taken near perihelion. Using spectroscopic and sublimation lifetime models, we set constraints on the physical properties of the ice grains in the coma, assuming they are responsible for the comet's hyperactivity. We rule out pure water-ice grains of any size, given their long lifetime. Instead, the hyperactivity of the nucleus and lack of water-ice absorption features in our spectra can be explained either by icy grains on the order of 1 μm in size with a small amount of low-albedo dust (greater than 0.5% by volume) or by large chunks containing significant amounts of water ice.

Keywords: Comae, Short period comets, Coma dust, Spectroscopy, Near infrared astronomy
Opposition Observations of 162173 Ryugu: Normal Albedo Map Highlights Variations in Regolith Characteristics. On 2019 January 8, the Telescopic Optical Navigation Camera (ONC-T) on board the Hayabusa2 spacecraft observed the Cb-type asteroid 162173 Ryugu under near-opposition illumination and viewing conditions from approximately 20 km in distance. Although opposition observations have never been used for mapping purposes of a planetary body, we found three advantages for mapping under these conditions: (1) images are free of topographic shadows, (2) the reflectance is nearly independent of the orientation of the surface, and (3) spurious color artifacts that may appear near shadowed terrain are avoided. We present normal albedo maps, one for each of the seven filters (0.40-0.95 μm), using an empirical photometric correction. Global coverage of Ryugu is 99.4%. The 0.55 μm band average normal albedo is 4.06% ± 0.10%. Various spectral variations are derived from these maps. Spectral features of regions and boulders are quantified by examining the normal albedo-derived spectral slope and UV index (spectral slope from visible to ultraviolet wavelength) value. In terms of space weathering, three spectral characteristics are observed over the majority of Ryugu: (1) reddening, (2) increases in reflectance at ultraviolet wavelengths compared to visible, and (3) darkening. By contrast, the bright boulders ("type 3") show a different trend, with wide variations in the 0.95 μm albedo and UV index. Finally, principal component analysis (PCA) comparisons with other asteroids strongly suggest that the main components of Ryugu belong to the B-Cb-type populations. The PCA feature of the fresh material on Ryugu is close to the Eulalia family.

Keywords: Near-Earth objects, Multi-color photometry, Small Solar System bodies, Asteroids, Surface photometry, Photometry
Spectrophotometric Properties of 162173 Ryugu's Surface from the NIRS3 Opposition Observations. Examination of the opposition geometry properties show that Ryugu's surface regolith is commensurate with laboratory studies of the photometric behavior of powdered carbonaceous chondrites. The regolith is consistent with a broad grain size distribution that contains a fine-grained component.

Keywords: Surface photometry, Asteroids, Spectroscopy
Morphological Evolution of Ordinary Chondrite Microstructure during Heating: Implications for Atmospheric Entry. Meteoroid entry physics remain poorly understood, owing to the extreme conditions experienced by the meteoroid during hypervelocity atmospheric passage, which are not reproducible in ground-test facilities. Therefore, much of our knowledge of fundamental processes is based on bolide lightcurve inference and a posteriori analysis of recovered meteorites. Here, novel in situ microtomography experiments at entry-relevant temperatures were performed on samples of two ordinary chondrites: Tamdakht (H5) and Tenham (L6). The two meteorites were imaged while undergoing a temperature ramp from room temperature to 1200°C. A machine-learning mediated analysis of the microstructural evolution reveals incongruent melting of the meteorite, initiated by the meteoritic iron and iron sulfide grains, and subsequent flow through microcracks that leads to the evolution of large voids. This behavior is correlated to a broad, high-temperature endotherm, noted from differential scanning calorimetry analysis, indicative of the heat of fusion of the melting grains. Correspondingly, a surface elemental analysis indicates that the sulfur species in iron sulfide are highly mobile, which can result in the formation of nonstoichiometric iron-sulfur compounds with melting points that span the temperature range of the observed endotherm. The implications for entry phenomena, in particular meteoroid ablation, are discussed.

Keywords: Meteorites, Chondrites, Meteoroids, Impact phenomena
Tracking Short-term Variations in the Haze Distribution of Titan's Atmosphere with SINFONI VLT. While it has long been known that Titan's haze and atmosphere are dynamic on seasonal timescales, recent results have revealed that they also exhibit significant subseasonal variations. Here, we report on observations of Titan acquired over an eight-month period between 2014 April and 2015 March with the Spectrograph for Integral Field Observations in the Near Infrared instrument on the Very Large Telescope using adaptive optics. These observations have an average five-day cadence, permitting interrogation of the short-period variability of Titan's atmosphere. Disk-resolved spectra in the H and K bands (1.4-2.4 μm) were analyzed with the PyDISORT radiative transfer model to determine the spatial distribution and variation of stratospheric haze opacity over subseasonal timescales. We observed a uniform decrease in haze opacity at 20°N and an increase in haze opacity at 250-300°E and ~40°N over the span of our observations. Globally, we found variations on the order of 5%-10% on timescales of weeks, as well as a steady, global increase in the amount of haze over timescales of months. The observed variations in haze opacity over the short timescales of our observations were of similar magnitude to long-period variations attributed to seasonal variation, suggesting rapid dynamical processes that may take part in the distribution of hazes in Titan's atmosphere.

Keywords: Saturnian satellites, Ground-based astronomy, Atmospheric variability
No Evidence for Time Variation in Saturn's Internal Magnetic Field. The time variation of a planetary magnetic field can reveal important aspects of a planet's interior structure. Searching for time variation in planetary magnetic fields other than Earth has proved challenging owing to the small number of spacecraft missions flown to date, but such a detection may be possible given a sufficiently long baseline for comparison. Here we leverage 38 years of spacecraft magnetometer measurements to search for time variation in Saturn's internal magnetic field. To isolate the possible signal of time variation, we remove a contemporary high-resolution internal field model, derived from Cassini data, as well as a best-fitting external magnetodisk field model from each of four past mission data sets: Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1981), and Cassini Saturn Orbit Insertion (2004). We then attempt to fit the resulting signal with an axisymmetric internal field model. Overall, we find no evidence of time variation on a multidecadal timescale. Our results lend support to the existence of a stably stratified layer in Saturn and have comparative planetology implications for Jupiter's interior structure and dynamics.

Keywords: Magnetic anomalies, Geomagnetic fields, Saturn, Jupiter, Magnetic fields, Planetary science, Planetary magnetospheres, Planetary interior
Exploring Ceres's Unusual Regolith Porosity and Its Implications for Volatile Retention. Asteroid Ceres, the only dwarf planet located in the inner solar system, shows unique surface mineralogy and geomorphology as observed by the Dawn mission. Of particular interest is understanding the role that upper regolith porosity plays in retaining volatiles and shaping Ceres' surface. Unfortunately, Ceres' near-surface porosity remains largely uncharacterized, compromising the ability to quantify volatile occurrence and identify the mechanisms for volatile retention at shallow depths, a topic of ongoing debate. Herein, we estimate Ceres' shallow-subsurface porosity by reinterpreting existing S- and X-band Earth-based radar observations combined with dielectric laboratory measurements of analog materials that have been recently suggested by spectral observations from the Dawn VIR spectrometer and in the far-ultraviolet from the Hubble telescope. Contrary to previous assumptions, our results suggest that Ceres' surface is more porous than the lunar regolith, with a bulk porosity ranging from ~53% to 72% or even higher in the top meter of the regolith, as opposed to ~39% to 50% for both bodies. The above suggests that Ceres' regolith is on average 15% more porous than the Moon, hence explaining its higher potential for volatile retention. We propose that lofting and gradual redeposition of fine particles by avalanches, continuous micrometeorite bombardment, and localized volatile outgassing are possible mechanisms for generating a globally high-porosity regolith. In addition to Ceres' proximity to the snowline of the early solar system, such a highly porous regolith may explain its efficiency at retaining volatiles at shallow depths into the present, as revealed by Dawn's GRaND observations.

Keywords: Planetary surfaces, Small Solar System bodies, Asteroids, Experimental techniques, Radar astronomy, Ceres, Dwarf planets
A Comprehensive Revisit of Select Galileo/NIMS Observations of Europa. The Galileo Near Infrared Mapping Spectrometer (NIMS) collected spectra of Europa in the 0.7-5.2 μm wavelength region, which have been critical to improving our understanding of the surface composition of this moon. However, most of the work done to get constraints on abundances of species like water ice, hydrated sulfuric acid, hydrated salts, and oxides has used proxy methods, such as absorption strength of spectral features or fitting a linear mixture of laboratory-generated spectra. Such techniques neglect the effect of parameters degenerate with the abundances, such as the average grain size of particles, or the porosity of the regolith. In this work we revisit three Galileo NIMS spectra, collected from observations of the trailing hemisphere of Europa, and use a Bayesian inference framework, with the Hapke reflectance model, to reassess Europa's surface composition. Our framework has several quantitative improvements relative to prior analyses: (1) simultaneous inclusion of amorphous and crystalline water ice, sulfuric-acid-octahydrate (SAO), CO2, and SO2; (2) physical parameters like regolith porosity and radiation-induced band-center shift; and (3) tools to quantify confidence in the presence of each species included in the model, constrain their parameters, and explore solution degeneracies. We find that SAO strongly dominates the composition in the spectra considered in this study, while both forms of water ice are detected at varying confidence levels. We find no evidence of either CO2 or SO2 in any of the spectra; we further show through a theoretical analysis that it is highly unlikely that these species are detectable in any 1-2.5 μm Galileo NIMS data.

Keywords: Planetary surfaces, Bayesian statistics, Chemical abundances, Europa, Surface ices, Spectroscopy, Radiative transfer simulations, Jovian satellites, Near infrared astronomy
Collisional Evolution of the Inner Zodiacal Cloud. The zodiacal cloud is one of the largest structures in the solar system and strongly governed by meteoroid collisions near the Sun. Collisional erosion occurs throughout the zodiacal cloud, yet it is historically difficult to directly measure and has never been observed for discrete meteoroid streams. After six orbits with Parker Solar Probe (PSP), its dust impact rates are consistent with at least three distinct populations: bound zodiacal dust grains on elliptic orbits (α-meteoroids), unbound β-meteoroids on hyperbolic orbits, and a third population of impactors that may be either direct observations of discrete meteoroid streams or their collisional by-products ("β-streams"). The β-stream from the Geminids meteoroid stream is a favorable candidate for the third impactor population. β-streams of varying intensities are expected to be produced by all meteoroid streams, particularly in the inner solar system, and are a universal phenomenon in all exozodiacal disks. We find the majority of collisional erosion of the zodiacal cloud occurs in the range of 10-20 solar radii and expect this region to also produce the majority of pickup ions due to dust in the inner solar system. A zodiacal erosion rate of at least ~100 kg s-1 and flux of β-meteoroids at 1 au of (0.4-0.8) × 10-4 m-2 s-1 are found to be consistent with the observed impact rates. The β-meteoroids investigated here are not found to be primarily responsible for the inner source of pickup ions, suggesting nanograins susceptible to electromagnetic forces with radii below ~50 nm are the inner source of pickup ions. We expect the peak deposited energy flux to PSP due to dust to increase in subsequent orbits, up to 7 times that experienced during its sixth orbit.

Keywords: Meteoroids, Interplanetary dust, Meteor streams, Circumstellar dust, Debris disks
Dust Directionality and an Anomalous Interplanetary Dust Population Detected by the Parker Solar Probe. Theory and previous space missions indicate there are several populations of zodiacal dust. The most prominent populations are grains on bound elliptic orbits (α-meteoroids), and β-meteoroids on hyperbolic escape trajectories governed largely by their size and composition. Yet, there may be other populations not yet confirmed by observation. The Parker Solar Probe (PSP) spacecraft is able to observe in situ dust populations in the densest part of the zodiacal cloud. Over the first seven orbits, dust count rates are well organized by orbital groups based on orbital parameters of PSP's shrinking orbit. In particular, the first three orbits and the sixth orbit have a single, preperihelion peak in count rate with a gradual drop off postperihelion, while Orbits 4, 5, and 7 have two distinct count rate peaks on either side of perihelion. The secondary peaks in Orbits 4, 5, and 7 are inconsistent with current zodiacal dust models that account for only two dust populations: α- and β-meteoroids. In examining the directionality of dust impacts on the PSP spacecraft, the presence of an anti-ram impactor anomaly postperihelion during Orbit 4 is evident. This anomaly may indicate another dust population beyond the nominal α- and β-meteoroids, and its origin may be related to the Geminids meteoroid stream associated with the asteroid 3200 Phaethon.

Keywords: Zodiacal cloud, Micrometeoroids
Exploring Tidal Obliquity Variations with SMERCURY-T. We introduce our new code, SMERCURY-T, which is based on existing codes SMERCURY and Mercury-T. The result is a mixed-variable symplectic N-body integrator that can compute the orbital and spin evolution of a planet within a multiplanet system under the influence of tidal spin torques from its star. We validate our implementation by comparing our experimental results to that of a secular model. As we demonstrate in a series of experiments, SMERCURY-T allows for the study of secular spin-orbit resonance crossings and captures for planets within complex multiplanet systems. These processes can drive a planet's spin state to evolve along vastly different pathways on its road toward tidal equilibrium, as tidal spin torques dampen the planet's spin rate and evolve its obliquity. Additionally, we show the results of a scenario that exemplifies the crossing of a chaotic region that exists as the overlap of two spin-orbit resonances. The test planet experiences violent and chaotic swings in its obliquity until its eventual escape from resonance as it tidally evolves. All of these processes are and have been important over the obliquity evolution of many bodies within the solar system and beyond and have implications for planetary climate and habitability. SMERCURY-T is a powerful and versatile tool that allows for further study of these phenomena.

Keywords: Exoplanet dynamics, Computational astronomy, Astronomy software, Computational methods, Astrobiology, Exoplanet tides, Habitable planets