Kilometers In Diameter Research Articles

Formation of the Naxos nested domes and crustal differentiation by convection and diapirism

The Naxos dome, in the middle of the Aegean domain, exposes the former root of the Alpine orogenic belt and represents a key natural example to investigate the development of gravitational instabilities during orogenic evolution and their impact on crustal differentiation. The Naxos dome is cored by migmatites with structures depicting second order domes with a diameter of 1–2 km nested in the first order deca-kilometer scale dome that formed at the onset of orogenic collapse. Zircon grains from the migmatites record a succession of crystallization-dissolution cycles with a period of 1–2 Myr. These features have been attributed to the development of convective and diapiric gravitational instabilities, related to thermally induced and compositional buoyancy. In this paper, we test the pertinence of this model with a thermal-mechanical numerical experiment performed with a volume of fluid method (VOF) known to preserve material phase interfaces during large deformation of viscous layers. Partial melting of the crust is modeled by strain-rate and temperature dependent viscosity and temperature dependent density. Moreover, horizontal layers with density, viscosity and heat production variations mimic more felsic or more mafic lithologies in a crust of intermediate composition. With basal heating, gravitational instabilities initiate with local segregation of the buoyant versus heavier layers, followed by diapiric upwelling of buoyant pockets of aggregated less dense material. Convection starts after 5 Myr, approximately when half of the crust has a viscosity lower than 1019 Pa s. The size of the convection cells increases as the temperature rises in the crust and reaches ∼25 km in diameter after ca. 20 Myr, which defines the size of first order domes. Some of the heterogeneous material is entrained in the convection cells with a revolution period of 1 to 3 Myr. However, most of the denser material accumulates in the lower crust, while the buoyant material segregates at the top of the convection cells and forms diapirs that correspond to second order domes, of several kilometers in diameter and nested within the first order domes. This model, which reproduces the first order characteristic dimensions of the Naxos nested domes and the periodicity of their zircon geochronological record, demonstrates the efficiency of gravitational instabilities in the formation of migmatite domes and, more generally, in the multi-scale dynamics of crustal differentiation leading to a felsic upper crust, an intermediate middle crust and a mafic lower crust.

Kinetic impact of a space vehicle with asteroid on collision course with earth

NEO (Near Earth Objects) are near-Earth space objects (asteroids and comets), whose orbit approaches the planet at one third of the average Earth-Sun distance. NEO are potentially capable of hitting Earth in the next century, with the exception of comets that can do so by the gravitational effect of Jupiter, pushing them into the Solar System. Current estimates1 indicate about 940 near-Earth objects larger than 1 kilometer in diameter. The US Congress has set targets for NASA's search for NEO, with 90% of them with a diameter of up to 1 km or greater in 10 years. This was motivated by a recent discovery in 2009 of a NEO approximately 2 to 3 km in diameter. These objects could cause global devastation if they hit Earth. In this research the NEO-Earth collision dynamics is studied and a statistic of physical and technological parameters is established as a mitigation strategy.

A quasi-objective single-buoy approach for understanding Lagrangian coherent structures and sea ice dynamics

Abstract. Sea ice drift and deformation, namely sea ice dynamics, play a significant role in atmosphere–ice–ocean coupling. Deformation patterns in sea ice can be observed over a wide range of spatial and temporal scales, though high-resolution objective quantification of these features remains difficult. In an effort to better understand local deformation of sea ice, we adapt the trajectory-stretching exponents (TSEs), quasi-objective measures of Lagrangian stretching in continuous media, to sea ice buoy data and develop a temporal analysis of TSE time series. Our work expands on previous ocean current studies that have shown TSEs provide an approximation of Lagrangian coherent structure diagnostics when only sparse trajectory data are available. As TSEs do not require multiple buoys, we find they have an expanded range of use when compared with traditional Eulerian buoy-array deformation metrics and provide local-stretching information below the length scales possible when averaging over buoy arrays. We verify the ability of TSEs to temporally and spatially identify dynamic features for three different sea ice datasets. The ability of TSEs to quantify trajectory stretching is verified by concurrent ice fracture in buoy neighborhoods ranging from tens to hundreds of kilometers in diameter, as well as the temporal concurrence of significant storm events.

Rubble pile asteroids are forever

Rubble piles asteroids consist of reassembled fragments from shattered monolithic asteroids and are much more abundant than previously thought in the solar system. Although monolithic asteroids that are a kilometer in diameter have been predicted to have a lifespan of few 100 million years, it is currently not known how durable rubble pile asteroids are. Here, we show that rubble pile asteroids can survive ambient solar system bombardment processes for extremely long periods and potentially 10times longer than their monolith counterparts. We studied three regolith dust particles recovered by the Hayabusa space probe from the rubble pile asteroid 25143 Itokawa using electron backscatter diffraction, time-of-flight secondary ion mass spectrometry, atom probe tomography, and 40Ar/39Ar dating techniques. Our results show that the particles have only been affected by shock pressure of ca. 5 to 15 GPa. Two particles have 40Ar/39Ar ages of 4,219 ± 35 and 4,149 ± 41 My and when combined with thermal and diffusion models; these results constrain the formation age of the rubble pile structure to ≥4.2 billion years ago. Such a long survival time for an asteroid is attributed to the shock-absorbent nature of rubble pile material and suggests that rubble piles are hard to destroy once they are created. Our results suggest that rubble piles are probably more abundant in the asteroid belt than previously thought and provide constrain to help develop mitigation strategies to prevent asteroid collisions with Earth.

Atmospheric Gamma-ray Observations at the Telescope Array Detector

Previously in AtmoHead-2018, we reported joint observations by Telescope Array Surface Detector (TASD), Lightning Mapping Array (LMA), sferic sensor and broadband interferometer of particle showers coincident with lightning. These consisted of energetic showers of approximately less than 10 microsecond duration with footprints on the ground of 3-6 kilometers in diameter, originating in the first one to two milliseconds of downward lightning leaders and coincident with high-current processes within the leaders. Scintillator waveform and simulation studies confirmed that these showers must consist primarily of gamma radiation.On September 11, 2021, atmospheric discharges emitting gamma rays were, for the first time, recorded by a high-speed camera and by lightning detectors on the ground simultaneously. The events were detected by the Telescope Array located in the Utah desert and were filmed by the Phantom v2012 camera, set at an acquisition rate of 40,000 frames per second (fps) in conjunction with the Lightning Mapping Array (LMA), an interferometer, a fast antenna, and the National Lightning Detection Network (NLDN). Results from this study reported the new observation of several events of significantly longer duration and higher uence, bridging the gap between the TASD and satellite-based detections. These events further demonstrate the similarity between the upward and downward TGF varieties and the likelihood of a common origin for their production.

Constraining the formation and transport of lunar impact glasses using the ages and chemical compositions of Chang'e-5 glass beads.

Impact glasses found in lunar soils provide a possible window into the impact history of the inner solar system. However, their use for precise reconstruction of this history is limited by an incomplete understanding of the physical mechanisms responsible for their origin and distribution and possible relationships to local and regional geology. Here, we report U-Pb isotopic dates and chemical compositions of impact glasses from the Chang’e-5 soil and quantitative models of impact melt formation and ejection that account for the compositions of these glasses. The predominantly local provenance indicated by their compositions, which constrains transport distances to <~150 kilometers, and the age-frequency distribution are consistent with formation mainly in impact craters 1 to 5 kilometers in diameter. Based on geological mapping and impact cratering theory, we tentatively identify specific craters on the basaltic unit sampled by Chang’e-5 that may have produced these glasses and compare their ages with the impact record of the asteroid belt.

Impact Structure Hidden Under Arctic Ice Dates to the Paleocene

Greenland’s Hiawatha impact structure, more than 30 kilometers in diameter, is much older than previously thought, new results suggest.

Characterizing ancient and modern hydrothermal venting systems

Ancient hydrothermal vent complexes have released large volumes of greenhouse gases in the past causing global warming, and similar modern vent structures are potential geohazards. In the NE Atlantic, thousands of hydrothermal vent complexes were formed during the Paleocene-Eocene Thermal Maximum. In Java, Indonesia, the erupting Lusi sediment-hosted geothermal system caused the displacement of 40,000 people. In order to determine how ancient and modern hydrothermal venting systems are related, we map a well-defined buried hydrothermal vent complex offshore mid-Norway using 3D seismic reflection data and then compare it to the active Lusi eruption (since 2006) and the neighboring inactive Porong Structure. These are characterized using 2D seismic reflection data, borehole data and field observations. The venting structures are subcircular in plan-view and a few kilometers in diameter. They are funnel-shaped in profiles, with inward-dipping beds surrounding the conduits. The hydrothermal vent complex offshore mid-Norway reveals five seismically-distinct vent fill facies units. Importantly, two of the facies units are separated by an angular unconformity, clearly indicating that the depositional events within the vent fill were distinct. Hydrothermal fluids are interpreted to have led to the fluidization of mud-rich sediments which were erupted and deposited in and around the vent complex. Interpretation of a seismically transparent body along the conduit of the Norwegian venting structure, and the abrupt widening of the conduit at the Porong Structure, are interpreted to be caused by changes in fluid-flow dynamics as the fluids rise and get released from the host-rock. The hydrothermal venting systems in Java and offshore mid-Norway are found to be morphologically similar and are interpreted to form as the result of the transport and eruption of fluidized sediments.

Tectono-magmatogenering structures in zones of increased geodynamic instability as priority objects for exploration of hydrogen fields

Based on comparison of the migration activity of hydrocarbons, helium and hydrogen, the paper substantiates the types of cap rocks for hydrogen accumulations (pools), which most of all contributes to its partial shieldingat steady feed. Such cap rocks are represented by predominantly smectite clay, pure (without inclusions) salt at depths over 1—2 km, non-fractured quartz sandstone at depths over 4 km, effusive and hypabissal intrusive rocks, as well as basement rocks undisturbed by metamorphic decomposition processes. Endogenous hydrogen isconsidered as the main factor of dissipative structures formation. Occurrence of hydrogen, hydrocarbon and ore macro accumulations is a kind of energy, information-geochemical fluctuations, which are intermediate states of dissipative structures subordinated to the planetary heat and mass transfer processes caused by the deep Earth degassing. In this context, the nature of geodynamic instability (activation of vertical movements, shifts, tensile and compressive stresses) can be considered as a growing sequence of dissipative processes associated with the energy percolation role of endogenous hydrogen. In the hierarchy of ring structures (RS) (from minor depressions to large structures of dozens kilometres in diameter) special attention should be paid to Sribne RS within the Dnieper-Donets Basin and Kaluga RS within the SW part of the Voronezh anteclisepericline. These ring structuresare genetically related to explosion or volcanic calderas, and characterized by ancient origin (Proterozoic) and long-term development, including neo- and actuotectonic stages. Intensity of hydrogen degassing in the Sribne RSis confirmed by micro- and nano-inclusions in the black-shale domanicoid rocks of the productive horizons in the form of particles of native metals(including oxyphile elements Al, Zn, W and others), natural alloys and intermetallids, which are tracers of ascending flows of deep reduced fluids. It is reasonable to assume the occurrence of a large hydrogen or helium-hydrogen field (group of fields) within the Sribne RS in the Lower Visean, Lower Bashkirian and Lower Permian aged rocks, which are shielded by the Lower Permian salt deposits.

An Improved Global Catalog of Lunar Impact Craters (≥1 km) With 3D Morphometric Information and Updates on Global Crater Analysis

AbstractImpact craters are common surface features on planetary surfaces. Their distribution offers important clues regarding geological and temporal processes on the Moon. Numerous endeavors have generated global catalogs of lunar craters; however, most of the existing catalogs only contain large craters (larger than several kilometers in diameter), and none of them offer three‐dimensional (3D) morphometric information. In this study, we first present a machine‐learning approach for automatic crater detection from digital elevation models (DEMs). Our crater detection approach can achieve a detection rate of about 85%. We also present an approach for extracting 3D morphometric information of craters based on the topography. These approaches were applied to producing a global crater data set covering the entire lunar surface that includes approximately 1.32 million craters (≥1 km). Verification was performed against previously published catalogs (Head et al., 2010, https://doi.org/10.1126/science.1195050; Robbins, 2019, https://doi.org/10.1029/2018je005592), with about 23% of our craters transferred from the previous catalogs after a rim‐fitting process. The crater catalog includes 3D morphometric data on the craters such as depths. Global analyses of craters based on this improved catalog indicate that the lunar mare and highlands have distinctive crater density differences of small craters (1–5 km). Craters of 2.5–5 km have reached saturation in several local regions in the highlands. Small craters (1–5 km) on the lunar mare are deeper than those on the highlands. The data in our comprehensive crater catalog can support various other lunar scientific studies.

Disintegration of Long-period Comet C/2019 Y4 (ATLAS). I. Hubble Space Telescope Observations

Abstract The near-Sun comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a three-day Hubble Space Telescope campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/2019 Y4-B and showed signs of significant mass loss and changes in size distribution throughout the three-day campaign. The cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of subsurface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before its disintegration. Gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of q = 0.25 au. We speculate that Comet ATLAS is derived from the ice-rich interior of a nonuniform, kilometer-wide progenitor that split during its previous perihelion. This suggests that comets down to a few kilometers in diameter can still possess complex, nonuniform interiors that can protect ices against intense solar heating.

Predicting Orbital Resonance of 2867 Šteins Using the Yarkovsky Effect

While gravitational forces have the largest impact on asteroid orbit determination, thermal forces such as the Yarkovsky and YORP effects also perturb asteroid orbits. We analyzed the impact of these thermal effects on the orbit of asteroid 2867 Šteins, an E-type asteroid measuring five kilometers in diameter. The orbit of Šteins lies within the range of a Kirkwood Gap, a region devoid of asteroids because of Jupiter’s gravitational pull. Given that thermal effects can perturb asteroids of similar properties, we sought to determine whether the Yarkovsky effect would push Šteins into a Kirkwood Gap within 50,000 years. Based on Šteins’ location and size, we hypothesized that the Yarkovsky effect will push Šteins into a Kirkwood gap. We computationally generated a thermal map of Šteins to approximate the Yarkovsky force and YORP torque. Analysis of the thermal map yielded an average Yarkovsky force parallel to velocity of -0.714 N and acceleration of -5.22 x 10-15 m/s2. The torque parallel to the angular velocity due to the YORP effect was 4.680 N m, with an angular acceleration of 1.217 x 10-20 rad/s2. We inputted the calculated Yarkovsky force into NASA’s GMAT to model the resulting change to Šteins’ orbit and found that the Yarkovsky force decays the semi-major axis of Šteins by 16.4 km in 242.2 years, and up to 5,365 km in 50,000 years within 95% confidence. This perturbation is unlikely to transfer Šteins into a Kirkwood Gap.

Meteoritic Evidence for a Ceres-sized Water-rich Carbonaceous Chondrite Parent Asteroid.

Carbonaceous chondrite meteorites record the earliest stages of Solar System geo-logical activities and provide insight into their parent bodies' histories. Some carbonaceous chondrites are volumetrically dominated by hydrated minerals, providing evidence for low temperature and pressure aqueous alteration1. Others are dominated by anhydrous minerals and textures that indicate high temperature metamorphism in the absence of aqueous fluids1. Evidence of hydrous metamorphism at intermediate pressures and temperatures in carbonaceous chondrite parent bodies has been virtually absent. Here we show that an ungrouped, aqueously altered carbonaceous chondrite fragment (numbered 202) from the Almahata Sitta (AhS) meteorite contains an assemblage of minerals, including amphibole, that reflect fluid-assisted metamorphism at intermediate temperatures and pressures on the parent asteroid. Amphiboles are rare in carbonaceous chondrites, having only been identified previously as a trace component in Allende (CV3oxA) chondrules2. Formation of these minerals requires prolonged metamorphism in a large (~640-1800 km diameter), unknown asteroid. Because Allende and AhS 202 represent different asteroidal parent bodies, intermediate conditions may have been more widespread in the early Solar System than recognized from known carbonaceous chondrite meteorites, which are likely a biased sampling.

Short-lived early Cenomanian volcanic atolls of Mt. Carmel, northern Israel

Volcanic atolls host exceptionally important marine ecosystems in the modern oceans. Yet, due to limited exposures, fossil atolls are poorly constrained. Multiple drowned Cretaceous volcanic atolls have been reported in the Pacific, but less information exists regarding those in the Tethys. Here we report on two early Cenomanian age volcanic atolls outcropping in Mt. Carmel (northern Israel), along the eastern Levant margin. These atolls are a few kilometers in diameter and differ significantly in facies from their surroundings, which are dominated by chalky calcareous mudstone and wackestone. The atolls are composed of grainstone, floatstone, rudstone and bafflestone facies, which are dominated by molluscans, notably gastropods, rudists, oysters and other bivalves. Corals and green algae are absent throughout these atolls. The studied sections of these atolls display a full succession, beginning with aggradation and ending with drowning. Age constraints for the volcanic phases suggest that deposition occurred within a relatively short time interval (<1 Myr) and the sequence represents a keep-up to give-up transition, within rising global and local sea-level trends. The inability of these atolls to keep up with rising sea level is attributed here to a suppressed carbonate factory, either due to drowning, turbidity and/or nutrient excess. Our study sheds new light on the dynamics of carbonate buildups during the Late Cretaceous and their ability to persist.

The formation of the cold classical Kuiper Belt by a short range transport mechanism

The Classical Kuiper Belt is populated by a group of objects with low inclination orbits, reddish colors and usually belonging to a binary system. This so called Cold Classical Kuiper Belt is considered to have been formed in situ from primordial ice pebbles that coagulated into planetesimals hundreds of kilometers in diameter. According to this scenario, the accretion of pebbles into large planetesimals would have occurred through the streaming instability mechanism that would be effective in the primordial Solar System disk of gas and solids. Nevertheless other objects with the same color characteristics as those found in the Cold Classical Kuiper Belt can be encountered also past the 2:1 mean motion resonance with Neptune as scattered or detached objects. Here I propose a mechanism that can account for both the cold Classical Kuiper Belt objects and other reddish objects outside the Classical Kuiper Belt. According to the proposed scenario, reddish objects were primordially in the outer portion of the planetesimal disk which was however truncated somewhere below ~42 au. In this manner the cold Classical Kuiper Belt and its scattered / detached counterpart were respectively transported outwards by a short range or slightly scattered to their present locations. Resonant objects were also formed by the same process. This mechanism is aimed at explaining the distribution of all objects that share the same color characteristics as coming from a common origin in the outer borders of the primordial planetesimal disk. According to the scenario here proposed the Cold Classical Kuiper Belt would have been formed ~4 au inside its present location with a total mass 20 − 100 times as large as its present value.

Suggestion that recent (≤ 3 Ga) flux of kilometer and larger impactors in the Earth-Moon system has not been constant

Lunar impact crater chronologies have been developed by combining carefully measured crater densities of lunar terrains with radiometric ages provided by returned samples. However, due to the sparse coverage of the samples during the last three billion years, this part of the chronologies is not well constrained. Lunar crater chronologies generally assume that the bombardment rate has been relatively constant during this epoch for all impactor sizes. Nevertheless, evidence has been gathering that this may not be the case for impactors larger than several hundred meters; however, there may be biases related to some of this evidence. The break-up of large asteroids in the Main Asteroid Belt to make asteroid families could be a source of a changing impact flux in the Earth-Moon system, especially when the families form near strong orbital resonances with the gas giants. In order to further explore the state of the impact flux from today to three billion years ago for impactors larger than ~5 km, we calculate crater retention model ages of 43 lunar craters 50 km and larger in diameter (D). Selected craters were initially suggested by United States Geological Survey geological maps of the Moon and Wilhems (1987) to have formed during the Copernican and Eratosthenian. We use the density of small (D < a few km) craters superposed on their floors, along with Model Production Function (MPF) lunar chronology (Marchi et al., 2009). For this purpose, we assume that the smaller impactors forming the superposed craters follow a constant flux as indicated by the MPF and supported by models of the dynamical evolution of the impactor population. We use the model ages as a proxy for the impact flux of larger impactors and test whether their distribution in time is consistent with a constant flux using two statistical analyses. Our results suggest that the flux of these larger impactors could be variable during the last three billion years, with hints of a relative increase in flux occurring ~2 billion years ago and a decrease in flux ~1 billion years ago. Thus, our results support the evidence that the impact flux has varied on the Moon for impactors over a few kilometers in diameter.

Abstract A11: Neighborhood clustering of bladder cancer incidence in Utah: Analyzing census data linked to cancer records

Abstract Evaluating risk factors across the lifespan (using the life course perspective) is important when considering the role of environment on BCa risk. Spatial cluster detection methods offer unique opportunities to identify shared exposures of individuals with BCa on the local level and formulate hypotheses about the potential role of environmental exposures. This study tests for evidence of spatial clustering of BCa incidence based on neighborhoods defined as 1940 US Census enumeration districts (ED). Data were extracted from the Utah Population Database (UPDB). UPDB holds birth, death, historic US Census, and driver license records that allow tracking of an individual’s location across the lifespan. UPDB is linked to the Utah Cancer Registry, an original member of the Surveillance, Epidemiology, and End Results program. Incident BCa cases from 1966 to 2017 were identified in the UCR or by death records and linked to UPDB. We geocoded all 1940 US Census ED centroids in Utah using US Census maps and ArcGIS software. The cohort comprises all individuals age 0–40 years at the time of the 1940 Census (Ncohort=343,521). We excluded individuals with an absence of follow-up information (Nexcluded=82,726). Our final cohort size was 260,795 individuals who contributed 13,816,670 person-years. SatScan software was used to identify spatial clustering of EDs with high rates of BCa. BCa was diagnosed in 2,654 individuals during follow-up (rate=19.2 cases per 100,000 person-years). Approximately 78.4% of cases were male. Average follow-up time was 53 years (range 1-78 years). We identified a circular cluster of 1.54 kilometers in diameter containing 23 ED centroids in an urban area, with a rate of 32.7 cases per 100,000 person-years (relative risk = 1.73, p=0.0023). We found evidence of spatial clustering of BCa incidence in an urban area of Salt Lake City, Utah for individuals in early life (0-40 years) at the time of the 1940 US Census. Individuals residing in this shared space were significantly more likely to develop BCa later in life, with a 73% increase in the incidence rate. Shared space in this context is presumed to be a proxy for environmental exposures. Environmental exposures including arsenic in drinking water and exposure to carcinogenic chemicals are associated with bladder cancer incidence. While this study was hypothesis generating and did not test for contaminants directly, future studies would benefit from the inclusion of contamination data. Additionally, we were limited by the use of residential history at a single time point and lack of data on personal behaviors (e.g., smoking). Strengths of this study include large cohort size, long follow-up time, and ability to expand to an early census. A life course perspective on cancer incidence provides for innovative methods to explore the environmental contexts of disease. Citation Format: Claire L. Leiser, Marissa Taddie, Rebecca Richards-Steed, James A. VanDerslice, Brock O’Neil, Heidi A. Hanson. Neighborhood clustering of bladder cancer incidence in Utah: Analyzing census data linked to cancer records [abstract]. In: Proceedings of the AACR Special Conference on Environmental Carcinogenesis: Potential Pathway to Cancer Prevention; 2019 Jun 22-24; Charlotte, NC. Philadelphia (PA): AACR; Can Prev Res 2020;13(7 Suppl): Abstract nr A11.

Fishing for “16 Psyche”

16 Psyche is one of the most massive asteroids in the asteroid belt. This object has a diameter of over 200 km and contains about 1% of the mass of the entire asteroid belt. It is believed to be the exposed iron core of a protoplanet and is the most massive metallic M-type asteroid. It was discovered by the Italian astronomer Annibale de Gasparis on March 17, 1852, in Naples and named after the Greek mythological figure Psyche. The prefix "16" means that it was the sixteenth minor planet in the order of discovery. 16 Psyche is the most massive metallic asteroid of type M. Radar observations indicate a fair pure iron-nickel composition. For a long time, scientists have imagined the possibility of fishing for metals from asteroids, or meteorites, close to our planet. Today, those predictions may come true. NASA is going to build a robot, called "Psyche", which will have the mission to explore an asteroid in the main asteroid belt between Mars and Jupiter. The asteroid "16 Psyche" has a diameter of 226 kilometers and is made of metals such as iron, nickel and gold. The metals that make up this unique asteroid could be worth more than $ 10 trillion. Radar observations indicate that Psyche has a dense and mostly metallic composition, consistent with one of the highest radar albedos in the asteroid belt (0.37±0.09). The psyche appears to have a surface that is 90% metallic and 10% silicate rock, with 6±1% orthopyroxene. Scientists believe that these metals can be mostly iron and nickel. NASA's infrared telescope installation at Mauna Kea Observatories reported evidence (~ 3 μm absorption characteristics) of hydroxyl ions on the asteroid in October 2016 that could suggest water ice. Because the psyche is believed to have formed in dry conditions without the presence of water, hydroxyl could have reached the psyche through previous impacts of low-carbon asteroids. The psyche appears to be an exposed metal core or a fragment of a metal core in a larger differentiated parent body, about 500 kilometers in diameter. If the Psyche is really one, there could be other asteroids in similar orbits. However, Psyche is not part of any identified asteroid family. One hypothesis is that the collision that formed the Psyche occurred very early in the history of the Solar System and all other remains were transformed into fragments by subsequent collisions or had their orbits beyond recognition. However, this scenario is considered to have a probability of only 1%. An alternative is that the psyche has been broken by impacts, but not catastrophically. In this case, it may be a candidate for the parent body of mesoseiderites (a class of meteorites with stony stones). Another possibility is that the Psyche is the end of the various relic bodies left by the formation of the inner planet. The asteroid's mantle may have been stripped not of a single collision, but of multiple (> 3) relatively slow side collisions with bodies of comparable or larger size. What is left is a metal core covered by a thin layer of silicates, which is revealed spectrally. In such a case, the Psyche would be analogous to Mercury, but much less massive.

Lunar megaregolith mixing by impacts: Spatial diffusion of basin melt and its implications for sample interpretation

The formation ages of lunar impact basins are critical to understanding the late accretion history of the inner solar system. Furthermore, the correct interpretation of the provenance and isotopic dates of basin-derived impact melt (‘basin melt’) is essential for the calibration of lunar chronology function. However, abundances of basin melt in the lunar near-surface are not well understood. Basin melt has been gardened by a long sequence of subsequent impact events, altering its abundance and size distribution. We developed a numerical model to investigate this process by means of the Monte Carlo method in a spatially resolved model. The fraction of melt in ejecta was tracked globally and at the Apollo 14–17 and Luna 20 sampling sites and was compared with K-Ar age distributions of lunar impact melt breccias. It was found that melt produced by the very large SPA basin as well as the relatively late-forming Imbrium basin should be dominant in the near-surface (top one meter). The simulation shows that the melt component at the Apollo 14–17 and Luna 20 sites is strongly affected by nearby mid- to late-forming basins. Imbrium melt should be abundant in Apollo 14–17 samples; Crisium melt is the most significant component of basin-sourced melt in Luna 20 samples; all the Apollo 14–17 and Luna 20 samples could include melt from Serenitatis and the SPA basin; Nectaris melt should occur in Apollo 16, Apollo 17 and Luna 20 samples; and Orientale melt has no significant mixing in the Apollo 14–17 and Luna 20 sampling sites. In general, besides a prominent age peak at 3.9 Ga (related to the Imbrium basin), the model predicts pronounced abundance peaks of older basin melt (>3.9 Ga) which tend to be absent from distributions of K-Ar ages of impactites from landing sites. The diffusion characteristics of basin melt suggest that for future sampling aimed at collecting early basin melt, the re-excavation zones of late impact craters larger than tens of kilometer in diameter inside basins may provide the highest abundances of melt from early basins.

Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper Belt object.

The Kuiper Belt is a distant region of the outer Solar System. On 1 January 2019, the New Horizons spacecraft flew close to (486958) 2014 MU69, a cold classical Kuiper Belt object approximately 30 kilometers in diameter. Such objects have never been substantially heated by the Sun and are therefore well preserved since their formation. We describe initial results from these encounter observations. MU69 is a bilobed contact binary with a flattened shape, discrete geological units, and noticeable albedo heterogeneity. However, there is little surface color or compositional heterogeneity. No evidence for satellites, rings or other dust structures, a gas coma, or solar wind interactions was detected. MU69's origin appears consistent with pebble cloud collapse followed by a low-velocity merger of its two lobes.