On 2022 September 29 the Juno spacecraft passed Europa at 355 km, the first close pass since the Galileo flyby in 2000. Juno's visible-light imager, JunoCam, collected four images, enabling cartographic, topographic, and surface geology analysis. The topography along the terminator is consistent with previously reported features that may indicate true polar wander. A bright band was discovered, and indicates global symmetry in the stress field that forms bright bands on Europa. The named feature Gwern is shown not to be an impact crater. Surface change detection shows no changes in 22 yr, although this is a difficult task considering differences between the JunoCam and Galileo imagers and very different viewing geometries. No active eruptions were detected.
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C. J. Hansen et al 2024 Planet. Sci. J. 5 76
Angelo Zinzi et al 2024 Planet. Sci. J. 5 103
The ASI cubesat LICIACube has been part of the first planetary defense mission DART, having among its scopes to complement the DRACO images to better constrain the Dimorphos shape. LICIACube had two different cameras, LEIA and LUKE, and to accomplish its goal, it exploited the unique possibility of acquiring images of the Dimorphos hemisphere not seen by DART from a vantage point of view, in both time and space. This work is indeed aimed at constraining the tridimensional shape of Dimorphos, starting from both LUKE images of the nonimpacted hemisphere of Dimorphos and the results obtained by DART looking at the impacted hemisphere. To this aim, we developed a semiautomatic Computer Vision algorithm, named VADER, able to identify objects of interest on the basis of physical characteristics, subsequently used as input to retrieve the shape of the ellipse projected in the LUKE images analyzed. Thanks to this shape, we then extracted information about the Dimorphos ellipsoid by applying a series of quantitative geometric considerations. Although the solution space coming from this analysis includes the triaxial ellipsoid found by using DART images, we cannot discard the possibility that Dimorphos has a more elongated shape, more similar to what is expected from previous theories and observations. The result of our work seems therefore to emphasize the unique value of the LICIACube mission and its images, making even clearer the need of having different points of view to accurately define the shape of an asteroid.
Norbert Schorghofer et al 2024 Planet. Sci. J. 5 99
Permanently shadowed regions (PSRs) in the north polar region of Ceres have been previously mapped by the Dawn spacecraft. Putative ice deposits are found in some of these PSRs, whereas most PSRs host no bright deposits, which is thought to be due to oscillations of the axis tilt with a ∼25 ka period. We use stereophotoclinometry to construct refined topographic models of PSR-hosting craters. Ray-tracing calculations reveal that no PSRs remain at the maximum axis tilt, which implies that the ice deposits are remarkably young. The bright ice deposits do not extend beyond PSRs at an axis tilt of 10°, which last occurred about 6 ka ago. This suggests that water is delivered to the polar regions or exposed within the craters by frequent and short-lived events. Surface temperatures are calculated with a terrain irradiance model to delineate cold traps. Based on maximum equilibrium temperatures, Cerean PSRs are too warm to trap supervolatiles.
Alexis Bouquet et al 2024 Planet. Sci. J. 5 102
We performed experiments of implantation of energetic sulfur ions (105 keV) into 2:1 water:propane ices at 80 K and analyzed the resulting refractory organic matter with ultrahigh-resolution mass spectrometry. Our goal was to characterize the organic matter processed in the surface conditions of Europa, where it would receive a heavy flux of energetic particles, including sulfur ions, and determine whether organosulfurs could be formed in these conditions, using the simplest alkane that can exist in solid form on Europa's surface. We find that the produced organic matter contains a large variety of both aliphatic and aromatic compounds (several thousand unique formulae), including polycyclic aromatic hydrocarbons (PAHs), with masses up to 900 amu. A large number of aromatic hydrocarbons is found along with oxygenated, mostly aliphatic, compounds. Organosulfurs are found in both CHS and CHOS form, demonstrating they can be formed from any organic compound through sulfur implantation. These organosulfurs' properties (aromaticity, mass) appear similar to the rest of the organic matter, albeit their low quantity does not allow for a thorough comparison. Our results have implications for the type of refractory organic matter that could be observed by the JUICE and Europa Clipper space missions and how the surface of Europa could generate complex organics, including PAHs and organosulfurs, that could then enrich the subsurface ocean. In particular, they indicate that a large diversity of organic matter, including organosulfurs, can be formed from simple precursors in a geologically short time frame under the ion flux that reaches Europa.
Francois-Xavier Schmider et al 2024 Planet. Sci. J. 5 100
We present three-dimensional (3D) maps of Jupiter's atmospheric circulation at cloud-top level from Doppler-imaging data obtained in the visible domain with JIVE, the second node of the JOVIAL network, which is mounted on the Dunn Solar Telescope at Sunspot, New Mexico. We report on 12 nights of observations between 2018 May 4 and May 30, representing a total of about 80 hr. First, the average zonal wind profile derived from our data is compatible with that derived from cloud-tracking measurements performed on Hubble Space Telescope images obtained in 2018 April from the Outer Planet Atmospheres Legacy program. Second, we present the first ever 2D maps of Jupiter's atmospheric circulation from Doppler measurements. The zonal velocity map highlights well-known atmospheric features, such as the equatorial hot spots and the Great Red Spot (GRS). In addition to zonal winds, we derive meridional and vertical velocity fields from the Doppler data. The motions attributed to vertical flows are mainly located at the boundary between the equatorial belts and tropical zones, which could indicate active motion in theses regions. Qualitatively, these results compare well to recent Juno data that have unveiled the 3D structure of Jupiter's wind field. To the contrary, the motions attributed to meridional circulation are very different from what is obtained by cloud tracking, except at the GRS. Because of limitations with data resolution and processing techniques, we acknowledge that our measurements of the vertical or meridional flows of Jupiter are still to be confirmed.
T. R. Watters et al 2024 Planet. Sci. J. 5 22
The lunar south pole regions are subjected to global stresses that result in contractional deformation and associated seismicity. This deformation is mainly expressed by lobate thrust fault scarps; examples are globally distributed, including polar regions. One small cluster of lobate scarps falls within the de Gerlache Rim 2 Artemis III candidate landing region. The formation of the largest de Gerlache scarp, less than 60 km from the pole, may have been the source of one of the strongest shallow moonquakes recorded by the Apollo Passive Seismic Network. The scarp is within a probabilistic space of relocated epicenters for this event determined in a previous study. Modeling suggests that a shallow moonquake with an Mw of ∼5.3 may have formed the lobate thrust fault scarp. We modeled the peak ground acceleration generated by such an event and found that strong to moderate ground shaking is predicted at a distance from the source of at least ∼40 km, while moderate to light shaking may extend beyond ∼50 km. Models of the slope stability in the south polar region predict that most of the steep slopes in Shackleton crater are susceptible to regolith landslides. Light seismic shaking may be all that is necessary to trigger regolith landslides, particularly if the regolith has low cohesion (on the order of ∼0.1 kPa). The potential of strong seismic events from active thrust faults should be considered when preparing and locating permanent outposts and pose a possible hazard to future robotic and human exploration of the south polar region.
M. J. Way et al 2022 Planet. Sci. J. 3 92
Large-scale volcanism has played a critical role in the long-term habitability of Earth. Contrary to widely held belief, volcanism, rather than impactors, has had the greatest influence on and bears most of the responsibility for large-scale mass extinction events throughout Earth's history. We examine the timing of large igneous provinces (LIPs) throughout Earth's history to estimate the likelihood of nearly simultaneous events that could drive a planet into an extreme moist or runaway greenhouse, leading to the end of volatile cycling and causing the heat death of formerly temperate terrestrial worlds. In one approach, we make a conservative estimate of the rate at which sets of near-simultaneous LIPs (pairs, triplets, and quartets) occur in a random history statistically the same as Earth's. We find that LIPs closer in time than 0.1–1 million yr are likely; significantly, this is less than the time over which terrestrial LIP environmental effects are known to persist. In another approach, we assess the cumulative effects with simulated time series consisting of randomly occurring LIP events with realistic time profiles. Both approaches support the conjecture that environmental impacts of LIPs, while narrowly avoiding grave effects on the climate history of Earth, could have been responsible for the heat death of our sister world Venus.
William F. Bottke et al 2024 Planet. Sci. J. 5 88
The origins of the giant planet satellites are debated, with scenarios including formation from a protoplanetary disk, sequential assembly from massive rings, and recent accretion after major satellite–satellite collisions. Here, we test their predictions by simulating outer solar system bombardment and calculating the oldest surface ages on each moon. Our crater production model assumes the projectiles originated from a massive primordial Kuiper Belt (PKB) that experienced substantial changes from collisional evolution, which transformed its size frequency distribution into a wavy shape, and Neptune's outward migration, which ejected most PKB objects onto destabilized orbits. The latter event also triggered an instability among the giant planets some tens of Myr after the solar nebula dispersed. We find all giant planet satellites are missing their earliest crater histories, with the likely source being impact resetting events. Iapetus, Hyperion, Phoebe, and Oberon have surface ages that are a few Myr to a few tens of Myr younger than when Neptune entered the PKB (i.e., they are 4.52–4.53 Gyr old). The remaining midsized satellites of Saturn and Uranus, as well as the small satellites located between Saturn's rings and Dione, have surfaces that are younger still by many tens to many hundreds of Myr (4.1–4.5 Gyr old). A much wider range of surface ages are found for the large moons Callisto, Ganymede, Titan, and Europa (4.1, 3.4, 1.8, and 0.18 Gyr old, respectively). At present, we favor the midsized and larger moons forming within protoplanetary disks, with the other scenarios having several challenges to overcome.
Shantanu P. Naidu et al 2024 Planet. Sci. J. 5 74
The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos, on 2022 September 26 UTC. We estimate the changes in the orbital and physical properties of the system due to the impact using ground-based photometric and radar observations, as well as DART camera observations. Under the assumption that Didymos is an oblate spheroid, we estimate that its equatorial and polar radii are 394 ± 11 m and 290 ± 16 m, respectively. We estimate that the DART impact instantaneously changed the along-track velocity of Dimorphos by −2.63 ± 0.06 mm s−1. Initially, after the impact, Dimorphos's orbital period had changed by −32.7 minutes ± 16 s to 11.377 ± 0.004 hr. We find that over the subsequent several weeks the orbital period changed by an additional 34 ± 15 s, eventually stabilizing at 11.3674 ± 0.0004 hr. The total change in the orbital period was −33.25 minutes ±1.5 s. The postimpact orbit exhibits an apsidal precession rate of 6.7 ± 02 day−1. Under our model, this rate is driven by the oblateness parameter of Didymos, J2, as well as the spherical harmonics coefficients, C20 and C22, of Dimorphos's gravity. Under the assumption that Dimorphos is a triaxial ellipsoid with a uniform density, its C20 and C22 estimates imply axial ratios, a/b and a/c, of about 1.3 and 1.6, respectively. Preimpact images from DART indicate Dimorphos's shape was close to that of an oblate spheroid, and thus our results indicate that the DART impact significantly altered the shape of Dimorphos.
Anicia Arredondo et al 2024 Planet. Sci. J. 5 37
We used the FORCAST instrument on SOFIA to obtain mid-infrared spectra (4.9–13.7 μm) of four S-type asteroids: (7) Iris, (11) Parthenope, (18) Melpomene, and (20) Massalia. Three of these four silicate-rich asteroids (Iris, Melpomene, and Massalia) were observed to have 3 μm features indicative of hydration by McAdam et al. We report a detection of a 6 μm feature that is unambiguously attributed to molecular water on two asteroids, Iris and Massalia, with peak heights of 4.532% ± 0.011% and 4.476% ± 0.012%, respectively. We estimate the abundance of molecular water based on these peak heights to be 454 ± 202 μg g−1 and 448 ± 209 μg g−1, consistent with values found on the sunlit Moon by SOFIA+FORCAST.
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Marzia Parisi et al 2024 Planet. Sci. J. 5 116
The most recent Planetary Science and Astrobiology Decadal Survey has proposed Uranus as the target for NASA's next large-scale mission. The interior structure and atmosphere of the planet are currently poorly understood, and objectives for investigating Uranus's deeper regions and composition are highly ranked. Traditionally, gravity science has served as one of the primary means for probing the depths of planetary bodies and inferring their internal density distributions. In this work, we present precise numerical simulations of an onboard radio science experiment designed to determine Uranus's gravity field and tidal deformations, which would offer a rare view into the planet's interior. We focus on the mission's orbital planning, discussing crucial parameters such as the number of pericenter passes, orbital inclination, and periapsis altitude necessary to meet the gravity measurement requirements for a Uranus orbiter. Our findings suggest that eight close encounters may be sufficient to determine the zonal gravity field up to J8 with a relative accuracy of 10%, if the trajectory is optimized. This would allow for the decoupling of the gravity field components due to interior structure and zonal winds. Additionally, we find that the expected end-of-mission uncertainty on Uranus's Love number k22 is of order ∼0.01 (3σ). This level of accuracy may offer crucial information about Uranus's inner state and allow for discriminating between a liquid and solid core, thus shedding light on crucial aspects of the planet's formation and evolution.
Tetyana Bila et al 2024 Planet. Sci. J. 5 115
We recently flew a new setup on parabolic flights for the first time to study particle motion on Martian slopes under Martian gravity. Here, we describe the initial experiments. We used dust/sand beds at varying ambient pressure of a few hundred pascals. The inclination of the particle bed was varied from 0° to 45° and parts of the surface were illuminated under varying conditions. We could observe downhill motion of material related to the insolation at the lowest light flux used of 591 ± 11 W m−2 for JSC Martian simulant. Motion occurred at significantly lower inclinations under illumination than without illumination, i.e., down to about 10° compared to about 20°–30°, respectively. We attribute this reduction in slope to thermal creep gas flow in the subsoil. This induces a Knudsen compressor, which supports grains against gravity and leads to smaller angles of repose. This is applicable to recurring slope lineae and slopes on Mars in general.
Trevor Austin et al 2024 Planet. Sci. J. 5 114
Impact-derived ejecta covers most of the lunar surface, originating from recent impacts through to the beginning of the geologic record. Despite how common ejecta is, accurate measurements of ejecta thickness are difficult to obtain, and existing estimates of ejecta thickness vary widely. This study uses excavation by meter-scale impacts on the fresh ejecta blankets of larger, kilometer-scale impacts to make point measurements of ejecta thickness. We estimate ejecta thickness at the rims of 73 lunar craters (0.1–4.8 km diameter) and create isopach maps of ejecta thickness for three craters. We derive an equation for ejecta thickness, , where r is the horizontal distance from the center of the crater, R is the center-to-rim crater radius, and B describes the rate at which ejecta thickness decays with radial distance. Our average value for B (2.8 ± 0.1) is similar to previous work, though we observe that B can vary significantly within an ejecta blanket.
Joseph R. Masiero et al 2024 Planet. Sci. J. 5 113
Asteroids with low orbital perihelion distances experience extreme heating from the Sun that can modify their surfaces and trigger nontypical activity mechanisms. These objects are generally difficult to observe from ground-based telescopes due to their frequent proximity to the Sun. The Near-Earth Object (NEO) Surveyor mission, however, will regularly survey down to solar elongations of 45° and is well suited for the detection and characterization of low-perihelion asteroids. Here, we use the survey simulation software tools developed for mission verification to explore the expected sensitivity of NEO Surveyor to these objects. We find that NEO Surveyor is expected to be >90% complete for near-Sun objects larger than D ∼ 300 m. Additionally, if the asteroid (3200) Phaethon underwent a disruption event in the past to form the Geminid meteor stream, Surveyor will be >90% complete to any fragments larger than D ∼ 200 m. For probable disruption models, NEO Surveyor would be expected to detect dozens of objects on Phaethon-like orbits, compared to a predicted background population of only a handful of asteroids, setting strong constraints on the likelihood of this scenario.
Michael T. Bland et al 2024 Planet. Sci. J. 5 112
Much of what we know about Neptune's moon Triton was inferred from the analysis of images returned by the Voyager 2 mission, the only spacecraft to have visited that putative ocean world. Unfortunately, the highest-resolution images (scales < 2 km pixel−1) are difficult to use because they are only available in nonstandard formats, and the locations of the images on Triton's surface are incorrect by up to 200 km. Although image mosaics of Triton are publicly available, these do not include the highest-resolution data. Here we describe our effort to improve the usability and accessibility of Voyager 2 images of Triton. We used the USGS's ISIS software to process 41 Triton images, including geometric calibration, radiometric calibration, and reseau removal. We improved the image locations using a photogrammetric control network with 958 points and 3910 image measurements. Least-squares bundle adjustment of the network yielded rms uncertainty of 0.50, 0.52, and 0.51 pixels in latitude, longitude, and radius, respectively, and maximum residuals of −4.21 and +3.20 pixels, respectively. Image-to-image alignment is therefore vastly improved. We have released these processed images as cloud-optimized GeoTIFFs in orthographic projection at the original pixel scale of each image. Associated mosaics have also been created and released to provide geologic context for the individual images. These products provide the science community with analysis-ready data that enable new investigations of Triton, increase accessibility to this unique data set, and continue to enhance the scientific return from the Voyager 2 mission.