Sazuna/UAT_keywords huggingface dataset:
Fractionation of Solar Wind Minor Ion Precipitation by the Lunar Paleomagnetosphere. The analysis of solar wind material implanted within lunar soil has provided significant insight into the makeup and evolutionary history of the solar wind and, by extension, the Sun and protosolar nebula. These analyses often rely on the tacit assumption that the Moon has served as an unbiased recorder of solar wind composition over its 4.5 billion yr lifetime. Recent work, however, has shown that for a majority of its lifetime, the Moon has possessed a dynamo that generates a global magnetic field with surface field strengths of at least 5 μT. In turn, the presence of such a field has been shown to significantly alter the lunar-solar wind interaction via the formation of a lunar "paleomagnetosphere." This paleomagnetosphere has implications for the flux of solar wind minor ions to the lunar surface and their subsequent implantation in lunar soil grains. Here we use a three-dimensional hybrid plasma model to investigate the effects of the lunar paleomagnetosphere on the dynamics and precipitation of solar wind minor ions to the lunar surface. The model results show that the lunar paleomagnetosphere can suppress minor ion fluxes to the lunar surface by more than an order of magnitude and strongly fractionates the precipitating solar wind in a complex, nonlinear fashion with respect to both the minor ion charge-to-mass ratio and the surface paleomagnetic field strength. We discuss the implications of these results with respect to both the analysis of trapped material in lunar grains and the semiquantitative 40Ar/36Ar antiquity indicator for lunar soils.

Keywords: Lunar magnetic fields, Planetary magnetospheres, Solar wind, The Moon
Terminator Double Layer Explorer (TerDLE): Examining the Near-Moon Lunar Wake. As the solar wind flows by the Moon, an antisunward-directed low-density wake forms as the plasma expands to fill in the trailing void in the plasma flow. Analytical modeling and modern plasma simulations suggest that plasma quasi-neutrality could possibly be broken close to the terminator obstruction as solar wind electrons expand into the wake ahead of the ions, leading to the formation of a standing (time-stationary) double layer. The objective of the Terminator Double Layer Explorer is to extend the fundamental understanding of the plasma expansion into the trailing near-vacuum wake region by (1) identifying any plasma expansion density anomalies at low altitudes near the terminator wake initiation region, (2) assessing the highly variable solar wind's effect on the low-altitude wake region, and (3) determining if plasma neutrality is maintained or lost during passages through the low-altitude expansion region. The mission concept uses a propulsion-driven CubeSat with ion spectrometer and plasma wave system in elliptical orbit about the Moon with periselene near the terminator. Over the course of the mission, the periselene decreases, placing the CubeSat ever closer to the terminator wake initiation location and the possible nonneutral region.

Keywords: Space plasmas, Plasma physics, Lunar science
The Reactivation of Main-belt Comet 259P/Garradd (P/2008 R1). We present observations of main-belt comet (MBC) 259P/Garradd from 4 months prior to its 2017 perihelion passage to 5 months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of ${\dot{M}}_{d}=(4.6\pm 0.2)$ kg s-1 (assuming grain densities of ρ = 2500 kg m-3 and a mean effective particle size of ${\bar{a}}_{d}=2$ mm) and a best-fit start date of detectable activity of 2017 April 22 ± 1, when the object was at a heliocentric distance of rh = 1.96 ∓ 0.03 au and a true anomaly of ν = 313°9 ± 0°4. We estimate the effective active fraction of 259P's surface area to be from fact ∼ 7 × 10-3 to fact ∼ 6 × 10-2 (corresponding to effective active areas of Aact ∼ 8 × 103 m2 to Aact ∼ 7 × 104 m2) at the start of its 2017 active period. A comparison of estimated total dust masses measured for 259P in 2008 and 2017 shows no evidence of changes in activity strength between the two active apparitions. The heliocentric distance of 259P's activity onset point is much smaller than those of other MBCs, suggesting that its ice reservoirs may be located at greater depths than on MBCs farther from the Sun, increasing the time needed for a solar-irradiation-driven thermal wave to reach subsurface ice. We suggest that deeper ice on 259P could be a result of more rapid ice depletion caused by the object's closer proximity to the Sun compared to other MBCs.

Keywords: Main belt asteroids, Comets, Main-belt comets
Solving the Alhazen-Ptolemy Problem: Determining Specular Points on Spherical Surfaces for Radiative Transfer of Titan's Seas. Given a light source, a spherical reflector, and an observer, where on the surface of the sphere will the light be directly reflected to the observer, i.e., where is the specular point? This is known as the Alhazen-Ptolemy problem and finding this specular point for spherical reflectors is useful in applications ranging from computer rendering to atmospheric modeling to GPS communications. Existing solutions rely upon finding the roots of a quartic equation and evaluating numerically which root provides the real specular point. We offer a formulation, and two solutions thereof, for which the correct root is predeterminable, thereby allowing the construction of the fully analytical solutions we present. Being faster to compute, our solutions should prove useful in cases that require repeated calculation of the specular point, such as Monte Carlo radiative transfer, including reflections off of Titan's hydrocarbon seas.

Keywords: Radiative transfer simulations, Titan, Natural satellite atmospheres, Natural satellite surfaces
Thermodynamically Governed Interior Models of Uranus and Neptune. Interior models of Uranus and Neptune often assume discrete layers, but sharp interfaces are expected only if major constituents are immiscible. Diffuse interfaces could arise if accretion favored a central concentration of the least volatile constituents (also, incidentally, the most dense); compositional gradients arising in such a structure would likely inhibit convection. Currently, two lines of evidence suggest possible hydrogen-water immiscibility in ice giant interiors. The first arises from crude extrapolation of the experimental H2-H2O critical curve to ∼3 GPa. The data are obtained for an impure system containing silicates, though Uranus and Neptune could also be "dirty." Current ab initio models disagree (Soubiran &amp; Militzer 2015), though hydrogen and water are difficult to model from first-principles quantum mechanics with the necessary precision. The second argument for H2-H2O immiscibility in ice giants, outlined herein, invokes reasoning about the gravitational and magnetic fields. While consensus remains lacking, here we examine the immiscible case. Applying the resulting thermodynamic constraints, we find that Neptune models with envelopes containing a substantial water mole fraction, as much as ${\chi }_{\mathrm{env}}^{{\prime} }\gtrsim 0.1$ relative to hydrogen, can satisfy observations. In contrast, Uranus models appear to require ${\chi }_{\mathrm{env}}^{{\prime} }\lesssim 0.01$ , potentially suggestive of fully demixed hydrogen and water. Enough gravitational potential energy would be available from gradual hydrogen-water demixing to supply Neptune's present-day heat flow for roughly 10 solar system lifetimes. Hydrogen-water demixing could slow Neptune's cooling rate by an order of magnitude; different hydrogen-water demixing states could account for the different heat flows of Uranus and Neptune.

Keywords: Neptune, Planetary interior, Planetary structure, Uranus
Voluminous Silica Precipitated from Martian Waters during Late-stage Aqueous Alteration. Mars' transition from an early "warm and wet" to a "cold and dry" environment left fingerprints on the geological record of fluvial activity on Mars. The morphological and mineralogical observations of aqueous activity provided varying constraints on the condition and duration of liquid water on the Martian surface. In this study, we surveyed the mineralogy of Martian alluvial fans and deltas and investigated the hydrated silica-bearing deposits associated with some of these landforms. Using CRISM data, we identified 35 locations across Mars with hydrated silica in proximity to fans/deltas, where the spectral characteristics are consistent with immature or dehydrated opal-A. In a few stepped fans/deltas, we find hydrated silica occurs within the bulk fan deposits and form sedimentary layers correlated with elevation. Meanwhile, in the older fans/deltas, silica mostly occurs at distal locations, and the relation to primary sedimentary deposits is more complex. We propose that the hydrated silica-bearing deposits in stepped fans/deltas likely formed authigenically from Martian surface waters, mainly during the Late Hesperian and Early Amazonian. These silica-bearing deposits could be a tracer for the temperature or duration of water involved in the formation of these deposits, given more precise and detailed observations of the sedimentary context, accessory minerals, the concentration of hydrated silica, and sediment-to-water ratio. Therefore, we consider that silica-bearing deposits should be among the most critical samples to investigate for future Mars missions, which are accessible in the landing sites of Mars 2020 and ExoMars 2022 missions.

Keywords: Planetary surfaces, Hydrosphere, Mars, Surface composition, Planetary structure
Ina Lunar Irregular Mare Patch Mission Concepts: Distinguishing between Ancient and Modern Volcanism Models. The Ina irregular mare patch, an ∼2 × 3 km summit depression on an ancient ∼22 km diameter shield volcano, displays two very enigmatic units: (1) dozens of dark convex-upward mounds and (2) a very rough, optically immature floor unit with very sharp morphologic contacts between the two. Controversy surrounds the age interpretation of Ina; superposed impact crater size-frequency distributions (CSFDs) suggest an age of ∼33 Ma, consistent with the presence of sharp contacts between the units and indicating that mare volcanism continues to today. Models of the terminal stages of volcano summit pit crater activity suggest an age coincident with the building of the shield, ∼3.5 Ga; these models interpret the CSFD age and sharp contacts to be due to an extremely porous lava lake floor and extrusion and solidification of magmatic foams. We present robotic-human exploration mission concepts designed to resolve this critical issue for lunar thermal evolution.

Keywords: Lunar maria, Lunar features, Lunar surface, Volcanoes, Lunar evolution, Planetary structure
Formation of the Lunar Dust Ejecta Cloud. The Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission orbited the Moon from 2014 September to 2015 April and observed a dynamic, permanently present dust cloud produced by continual meteoroid bombardment. For the latitudes observed by LDEX, the sporadic background contribution to the impacting dust flux is dominated by helion (HE), apex (AP), and antihelion (AH) sources oscillating with lunar phase. Using improved impact ejecta distributions, a three-dimensional model was implemented to estimate the inner and outer ejecta cone angles from LDEX plume measurements. Expanding upon this single-plume model and the derived ejecta cone angles, we implemented a global lunar model fitted to LDEX measurements of the sporadic background to constrain the product of meteoroid impactor fluxes and ejecta mass yield per source. We use the observed asymmetry between sunward and antisunward impactor fluxes to discuss the possible contributions of β-meteoroids, in addition to the HE and AH sporadic meteoroid sources. We find that if β-meteoroids are responsible for the day/night asymmetry, they must have an impact ejecta yield of at least 103.

Keywords: The Moon, Meteoroids
The Role of Hydrated Minerals and Space Weathering Products in the Bluing of Carbonaceous Asteroids. The surfaces of airless bodies such as lunar and S-type asteroids typically become spectrally redder in visible to near-infrared reflectance with longer exposures to space weathering. However, some carbonaceous asteroids instead become spectrally bluer. Space weathering experiments on carbonaceous meteorites have provided some clues as to the space weathering products that could produce spectral bluing. We applied these experimental results to our Hapke radiative transfer model, with which we modeled spectral data from the OSIRIS-REx mission in order to determine whether these space weathering products—specifically, nanophase and microphase metallic iron, troilite, and magnetite—could explain the globally blue spectrum of the carbonaceous asteroid (101955) Bennu. The model suggests that the surface of Bennu has microphase iron, nanophase magnetite, and nanophase and microphase troilite. Considering previous space weathering experiments together with our spectral modeling of Bennu, we posit that the presence of nanophase magnetite is what causes a carbonaceous asteroid to become spectrally bluer with exposure time. Nanophase magnetite can form on asteroids that have Fe-bearing hydrated minerals (phyllosilicates). On anhydrous carbonaceous asteroids, nanophase iron forms instead of magnetite, leading to spectral reddening. We therefore predict that samples returned by the OSIRIS-REx mission from Bennu will have more nanophase magnetite than nanophase iron with nanophase and microphase sulfides, whereas samples returned by the Hayabusa2 mission from the carbonaceous asteroid (162173) Ryugu, which is spectrally red, will contain nanophase and microphase sulfides as well as more nanophase iron than nanophase magnetite.

Keywords: Near-Earth objects, Planetary surfaces, Spectroscopy
Dynamical Tides in Jupiter as Revealed by Juno. The Juno orbiter has continued to collect data on Jupiter's gravity field with unprecedented precision since 2016, recently reporting a nonhydrostatic component in the tidal response of the planet. At the mid-mission perijove 17, Juno registered a Love number k2 = 0.565 ± 0.006 that is -4% ± 1% (1σ) from the theoretical hydrostatic ${k}_{2}^{(\mathrm{hs})}=0.590$ . Here we assess whether the aforementioned departure of tides from hydrostatic equilibrium represents the neglected gravitational contribution of dynamical tides. We employ perturbation theory and simple tidal models to calculate a fractional dynamical correction Δk2 to the well-known hydrostatic k2. Exploiting the analytical simplicity of a toy uniform-density model, we show how the Coriolis acceleration motivates the negative sign in the Δk2 observed by Juno. By simplifying Jupiter's interior into a coreless, fully convective, and chemically homogeneous body, we calculate Δk2 in a model following an n = 1 polytrope equation of state. Our numerical results for the n = 1 polytrope qualitatively follow the behavior of the uniform-density model, mostly because the main component of the tidal flow is similar in each case. Our results indicate that the gravitational effect of the Io-induced dynamical tide leads to Δk2 = - 4% ± 1%, in agreement with the nonhydrostatic component reported by Juno. Consequently, our results suggest that Juno obtained the first unambiguous detection of the gravitational effect of dynamical tides in a gas giant planet. These results facilitate a future interpretation of Juno tidal gravity data with the purpose of elucidating the existence of a dilute core in Jupiter.

Keywords: Gravitational fields, Jupiter, Tides, Galilean satellites, Planetary interior
On the Tidal History and Future of the Earth-Moon Orbital System. Earth's rotation rate and the evolution of the Earth-Moon system have been controlled by tidal dissipation in Earth's ocean. Attempts to model the tidal history have shown incomplete compatibility with observations and unclear isolation of the most important controlling factors. Here it is shown that a relatively simple model with no explicit description of the continents (their effects are instead parameterized) can accurately reproduce the available observations (lunar distance and month, Earth's rotation and deceleration rates) describing the tidal evolution over the past 2.5 billion yr and also evade the paradox of an early Moon falling within the Roche limit. Notably, the model reproduces an observed dissipation peak 400 million yr ago. The model involves fitting two input parameters (the effective ocean depth h and the nondimensional dissipation timescale $\tilde{T}$ , the latter of which can be related to the more typically used quality factor Q). The best-fit values (h = 2.3 km and $\tilde{T}=40$ , corresponding to Q ≈ 20-28) derived empirically from the model correspond well with the plausibly expected values (h ≈ 2.5 km and Q ≈ 20) derived using independent reasoning and observations. The model shows very clearly that the tidal evolution has been primarily controlled by the rate of resonance in the ocean response, not the evolving amplitude of the tidal forces or forcing frequency. More closely, it also shows that the effect of Earth's rotation on the Lamb parameter (or nondimensional wave speed) has driven the evolution, and that changes in frequency or other parameters have been much less important.

Keywords: Ocean planets, Natural satellite dynamics, Orbital evolution, Lunar evolution, Ocean tides, Earth-moon system
Venus Observations at 40 and 90 GHz with CLASS. Using the Cosmology Large Angular Scale Surveyor, we measure the disk-averaged absolute Venus brightness temperature to be 432.3 ± 2.8 K and 355.6 ± 1.3 K in the Q and W frequency bands centered at 38.8 and 93.7 GHz, respectively. At both frequency bands, these are the most precise measurements to date. Furthermore, we observe no phase dependence of the measured temperature in either band. Our measurements are consistent with a CO2-dominant atmospheric model that includes trace amounts of additional absorbers like SO2 and H2SO4.

Keywords: Atmospheric composition, Brightness temperature, Venus
Cold Traps of Hypervolatiles in the Protosolar Nebula at the Origin of the Peculiar Composition of Comet C/2016 R2 (PanSTARRS). Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N2/CO abundance ratio, typically larger than ∼0.05, and at least 2-3 times higher than the one measured in 67P/Churyumov-Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O (H2O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed low water abundance. We then alternatively investigate the possibility that the building blocks of R2 agglomerated from grains and pebbles made of pure condensates via the use of a disk model describing the radial transport of volatiles. We show that N2/CO ratios reproducing the value estimated in this comet can be found in grains condensed in the vicinity of the CO and N2 ice lines. Moreover, high CO/H2O ratios (&gt;100 times the initial gas-phase value) can be found in grains condensed in the vicinity of the CO ice line. If the building blocks of a comet assembled from such grains, they should present N2/CO and CO/H2O ratios consistent with the measurements made in R2's coma. Our scenario indicates that R2 formed in a colder environment than the other comets that share more usual compositions. Our model also explains the unusual composition of the interstellar comet 2l/Borisov.

Keywords: Solar system formation, Solar system, Planetary system formation, Protoplanetary disks, Comet origins, Comet volatiles
Optical Constants of a Solar System Organic Analog and the Allende Meteorite in the Near- and Mid-infrared (1.5-13 μm). Measurements of visible and near-infrared reflection (0.38-5 μm) and mid-to-far-infrared emission (5-200 μm) from telescope and satellite remote-sensing instruments make it possible to investigate the composition of planetary surfaces via electronic transitions and vibrational modes of chemical bonds. Red spectral slopes at visible and near-infrared wavelengths and absorption features at 3.3 and 3.4 μm observed in circumstellar disks, in the interstellar medium (ISM), and on the surfaces of solar system bodies are interpreted to be due to the presence of organic material and other carbon compounds. Identifying the origin of these features requires measurements of the optical properties of a variety of relevant analog and planetary materials. Spectroscopic models of dust within circumstellar disks and the ISM, as well as planetary regoliths, often incorporate just one such laboratory measurement despite the wide variation in absorption and extinction properties of organic and other carbon-bearing materials. Here we present laboratory measurements of transmission spectra in the 1.5-13 μm region and use these to derive real and imaginary indices of refraction for two samples: (1) an analog to meteoritic insoluble organic matter and (2) a powdered Allende meteorite sample. We also test our refractive index retrieval method on a previously published transmission spectrum of an Mg-rich olivine. We compare optical measurements of the insoluble organic matter analog to those of other solar system and extrasolar organic analogs, such as amorphous carbon and tholins, and find that the indices of refraction of the newly characterized material differ significantly from other carbonaceous samples.

Keywords: Circumstellar dust, Interplanetary dust, Meteorite composition, Transmission spectroscopy
Modeling Saturn's D68 Clumps as a Co-orbital Satellite System. The D68 ringlet is the innermost feature in Saturn's rings. Four clumps that appeared in D68 around 2014 remained evenly spaced about 30° apart and moved very slowly relative to each other from 2014 up until the last measurements were taken in 2017. D68's narrowness and the distribution of clumps could either indicate that we have a collection of source bodies in a co-orbital configuration or imply that an outside force confines the observed dust and any source bodies. In this paper we explore the possibility that these four clumps arose from four source bodies in a co-orbital configuration. We find that there are no solutions with four masses that produce the observed spacings. We therefore consider whether an unseen fifth co-orbital object could account for the discrepancies in the angular separations and approach a stable stationary configuration. We find a range of solutions for five co-orbital objects where their mass ratios depend on the assumed location of the fifth mass. Numerical simulations of five co-orbitals are highly sensitive to initial conditions, especially for the range of masses we would expect the D68 clumps to have. The fragility of our D68 co-orbital system model implies that there is probably some outside force confining the material in this ringlet.

Keywords: Orbits, Planetary rings, Dynamical evolution