The Martian Moons eXploration (MMX) mission will study the Martian moons Phobos and Deimos, Mars, and their environments. The mission scenario includes both landing on the surface of Phobos to ...collect samples and deploying a small rover for in situ observations. Engineering safeties and scientific planning for these operations require appropriate evaluations of the surface environment of Phobos. Thus, the mission team organized the Landing Operation Working Team (LOWT) and Surface Science and Geology Sub-Science Team (SSG-SST), whose view of the Phobos environment is summarized in this paper. While orbital and large-scale characteristics of Phobos are relatively well known, characteristics of the surface regolith, including the particle size-distributions, the packing density, and the mechanical properties, are difficult to constrain. Therefore, we developed several types of simulated soil materials (simulant), such as UTPS-TB (University of Tokyo Phobos Simulant, Tagish Lake based), UTPS-IB (Impact-hypothesis based), and UTPS-S (Simpler version) for engineering and scientific evaluation experiments.
Noncoding variants of presumed regulatory function contribute to the heritability of neuropsychiatric disease. A total of 2,221 noncoding variants connected to risk for ten neuropsychiatric ...disorders, including autism spectrum disorder, attention deficit hyperactivity disorder, bipolar disorder, borderline personality disorder, major depression, generalized anxiety disorder, panic disorder, post-traumatic stress disorder, obsessive-compulsive disorder and schizophrenia, were studied in developing human neural cells. Integrating epigenomic and transcriptomic data with massively parallel reporter assays identified differentially-active single-nucleotide variants (daSNVs) in specific neural cell types. Expression-gene mapping, network analyses and chromatin looping nominated candidate disease-relevant target genes modulated by these daSNVs. Follow-up integration of daSNV gene editing with clinical cohort analyses suggested that magnesium transport dysfunction may increase neuropsychiatric disease risk and indicated that common genetic pathomechanisms may mediate specific symptoms that are shared across multiple neuropsychiatric diseases.
Abstract
We overview various efforts within the DART Investigation Team’s Ejecta Working Group to predict the characteristics, quantity, dynamical behavior, and observability of DART impact ejecta. ...We discuss various methodologies for simulation of the impact/cratering process with their advantages and drawbacks in relation to initializing ejecta for subsequent dynamical propagation through and away from the Didymos system. We discuss the most relevant forces acting on ejecta once decoupled from Dimorphos’s surface and highlight various software packages we have developed and used to dynamically simulate ejecta under the action of those forces. With some additional software packages, we explore the influence of additional perturbing effects, such as interparticle collisions within true
N
-body codes and nonspherical and rotating particles’ interplay with solar radiation pressure. We find that early-timescale and close-proximity ejecta evolution is highly sensitive to some of these effects (e.g., collisions) while relatively insensitive to other factors. We present a methodology for turning the time-evolving size- and spatially discretized number density field output from ejecta simulations into synthetic images for multiple platforms/cameras over wide-ranging vantage points and timescales. We present such simulated images and apply preliminary analyses to them for nominal and off-nominal cases bracketing realistic total mass of ejecta and ejecta cumulative size–frequency distribution slope. Our analyses foreshadow the information content we may be able to extract from the actual images taken during and after the DART encounter by both LICIACube and Earth-vicinity telescopes.
The first verifiable near-infrared absorption features in the ∼0.9-μm spectral region are reported for Asteroids 16 Psyche, 69 Hesperia, 110 Lydia, 125 Liberatrix, 201 Penelope, and 216 Kleopatra. ...These weak features (
∼
1
–
3
%
) are attributed to orthopyroxenes present on the surfaces of these asteroids. 16 Psyche and 125 Liberatrix have full rotational coverage while 69 Hesperia, 110 Lydia, 201 Penelope, and 216 Kleopatra have
∼
75
%
rotational coverage. Qualitative ∼2-μm absorption features are present, but are very weak (
<
1
%
). Absorption band positions suggest relatively low abundances of calcium and iron in the pyroxenes. This indicates relatively reducing redox conditions for these asteroids, their parent bodies, and the nebular regions in which they formed. Four potential interpretations for these asteroids include: (1) they are exposed metallic cores or core fragments of differentiated parent bodies with residual orthopyroxene mantle material, (2) they are the result of a smelting-like reaction that converts olivine to pyroxene and metallic iron in the presence of carbon at high temperatures, (3) they are analogs to the primitive metal-rich Bencubbinite meteorites, or (4) they represent metallic surfaces which have accumulated silicate debris from external sources. Of the two original interpretations for the M-asteroids, the enstatite chondrite interpretation (Chapman and Salisbury, 1973, Icarus 19, 507–522; Gaffey and McCord, 1979, Mineralogical and petrological characterizations of asteroids. In: Gehrels T. (Ed.), Asteroids. Univ. of Arizona Press, Tucson, pp. 688–723) can be eliminated for these asteroids because the pyroxene in enstatite chondrites is iron-free and does not exhibit such absorption features. The iron meteorite interpretation remains valid, but with modification. For M-Asteroids 16 Psyche and 216 Kleopatra, these spectral results combined with previous determinations of high radar albedos indicate that these bodies are most probably exposed core fragments of differentiated bodies. M-Asteroids 69 Hesperia, 110 Lydia, 125 Liberatrix, and 201 Penelope exhibit similar spectral features consistent with exposed core fragments, but radar observations would be needed to confirm a high metal abundance. Observations of M-Asteroids 136 Austria and 325 Heidelberga suggest the absence of absorption features in the ∼0.4- to ∼2.5-μm region within the scatter of the data. Verification of the presence or absence of features across the surfaces of these two asteroids requires full rotational coverage. The interpretations for these “featureless” M-asteroids are not well-constrained, but remain consistent with the iron meteorite and enstatite chondrite interpretations.
► We studied composition of near-Earth Asteroid 2008 EV5. ► It is potential target for Marco Polo-R and Hayabusa-2 mission proposals. ► Composition is similar to a dark carbonaceous chondrite ...dominated surface. ► A weak 0.48-μm spin-forbidden Fe3+ absorption band has been detected. ► Most plausible meteorite analog is CI chondrite such as Orgueil.
We observed Potentially Hazardous Asteroid (PHA) 2008 EV5 in the visible (0.30–0.92μm) and near-IR (0.75–2.5μm) wavelengths to determine its surface composition. This asteroid is especially interesting because it is a potential target for two sample return mission proposals (Marco Polo-R and Hayabusa-2) and human exploration due to its low delta-v for rendezvous. The spectrum of 2008 EV5 is essentially featureless with exception of a weak 0.48-μm spin-forbidden Fe3+ absorption band. The spectrum also has an overall blue slope. The albedo of 2008 EV5 remains uncertain with a lower limit at 0.05 and a higher end at 0.20 based on thermal modeling. The Busch et al. (Busch et al. 2011. Icarus 212, 649–660) albedo estimate of 0.12±0.04 is consistent with our thermal modeling results. The albedo and composition of 2008 EV5 are also consistent with a C-type taxonomic classification (Somers, J.M., Hicks, M.D., Lawrence, K.J. 2008. Bull. Am. Astron. Soc. 40, 440). The best spectral match is with CI carbonaceous chondrites similar to Orgueil, which also have a weak 0.48-μm feature and an overall blue slope. This 0.48-μm feature is also seen in the spectrum of magnetite. The albedo of CI chondrites is at the lower limit of our estimated range for the albedo of 2008 EV5.
► We report observations from 2012 of the Hayabusa II target asteroid 1999 JU3. ► Broadband photometry suggests a rotation period of 7.631±0.005h. ► Thermally altered carbonaceous chondrites are ...visible+near-IR spectral analogs. ► Our rotationally-resolved visible spectra are featureless and show no variability. ► Previously reported surface heterogeneity must be limited to <5% of the asteroid’s surface area.
The Japanese Space Agency’s Hayabusa II mission is scheduled to rendezvous with and return a sample from the near-Earth Asteroid (162173) 1999 JU3. Previous visible-wavelength spectra of this object show significant variability across multiple epochs which has been attributed to a compositionally heterogeneous surface. We present new visible and near-infrared spectra to demonstrate that thermally altered carbonaceous chondrites are plausible compositional analogs, however this is a tentative association due to a lack of prominent absorption features in our data. We have also conducted a series of high signal-to-noise visible-wavelength observations to investigate the reported surface heterogeneity. Our time series of visible spectra do not show variability at a precision level of a few percent. This result suggests two most likely possibilities. One, that the surface of 1999 JU3 is homogenous and that unaccounted for systematic effects are causing spectral variation across epochs. Or two, that the surface of 1999 JU3 is regionally heterogenous, in which case existing shape models suggest that any heterogeneity must be limited to terrains smaller than approximately 5% of the total surface area. These new observations represent the last opportunity before both the launch and return of the Hayabusa II spacecraft to perform ground-based characterization of this asteroid. Ultimately, these predictions for composition and surface properties will be tested upon completion of the mission.
► We observed 12 near-Earth asteroids to constrain their albedo, diameter and composition using their near-infrared spectrum. ► Our albedo and diameter estimates are consistent with those obtained by ...thermal-IR and radar observations. ► Composition of the asteroids we observed ranges from low albedo carbonaceous chondrites to bright enstatite achondrites.
We present a method to constrain the albedo and diameters of near-Earth asteroids (NEAs) based on thermal flux in their near-infrared spectra (0.7–2.5μm) using the Standard Thermal Model. Near-infrared spectra obtained with the SpeX instrument on NASA Infrared Telescope Facility are used to estimate the albedo and diameters of 12 NEAs (1992 JE, 1992 UY4, 1999 JD6, 2004 XP14, 2005 YY93, 2007 DS84, 2005 AD13, 2005 WJ56, 1999 JM8, 2005 RC34, 2003 YE45, and 2008 QS11). Albedo estimates were compared with average albedo for various taxonomic classes outlined by Thomas et al. (Thomas, C.A. et al. 2011. Astron. J. 142(3)) and are consistent with their results. Spectral band parameters, like band centers, are derived and compared to spectra of laboratory mineral mixtures and meteorites to constrain their composition and possible meteorite analogs. Based on our study we estimate the albedos and diameters of these NEAs and compare them with those obtained by other techniques such as ground-based mid-infrared, Spitzer thermal infrared and Arecibo radar. Our results are broadly consistent with the results from other direct methods like radar. Determining the compositions of low albedo asteroids is a challenge due to the lack of deep silicate absorption features. However, based on weak absorption features and albedo, we suggest possible meteorite analogs for these NEAs, which include black chondrites, CM2 carbonaceous chondrites and enstatite achondrites. We did not find any specific trends in albedo and composition among the asteroids we observed.
Abstract
Quantifying variability in, and identifying the mechanisms behind, East Asian dust production and transport across the last several million years is essential for constraining future dust ...emissions and deposition. Our current understanding of East Asian dust dynamics through the Quaternary is primarily limited to low‐resolution records from the North Pacific Ocean, those from the Chinese Loess Plateau (CLP), and paleoenvironmental reconstructions from arid basins. All are susceptible to sediment winnowing and focusing as well as input of poorly constrained or unidentified non‐dust detrital material. To avoid these limitations, we examine high‐resolution, constant flux proxy‐derived dust fluxes from the North Pacific and find evidence for higher glacial dust fluxes in the late Pliocene‐early Pleistocene compared to the late Pleistocene‐Holocene. Our results suggest decreasing dust transported to the mid‐latitude North Pacific Ocean from eastern Asia across the Quaternary. This observation is ostensibly at odds with previous dust records from marine sediments and the CLP, and with the perception of higher East Asian dust production and transport during the late Pleistocene associated with the amplification of glaciations. We provide three possible scenarios to describe the ∼2,700‐ky evolution of eastern Asia glacial dust dynamics, and discuss them in the context of sediment production, availability, and atmospheric circulation. Our data and proposed driving mechanisms not only raise questions about the framework typically used to interpret dust archives from East Asia and the North Pacific Ocean, but also provide a roadmap for hypothesis testing and future work necessary to produce better‐constrained records of paleo‐dust fluxes.
Key Points
Constant flux proxy‐derived glacial dust fluxes to the North Pacific decrease between the early and late Quaternary
Reduced glacial dust fluxes may be a result of shifting dust production dynamics and/or atmospheric circulation
Chinese Loess Plateau accumulation rates may need to be reevaluated when considered for paleoclimate reconstructions
Detailed near-infrared spectral observations of Asteroid 1459 Magnya reveal an asteroid that is primarily composed of pyroxene and plagioclase feldspar, confirming earlier suggestions that Magnya has ...a basaltic composition. The average Magnya spectrum for March 23, 2002 has a Band I center of 0.926 μm and a Band II center of 1.938 μm. Observations over
4
1
2
hours show little variation in band center positions. The feldspar-to-pyroxene ratio is ∼0.6 on Magnya's surface. Comparing Magnya with the spectral parameters from 4 Vesta shows discordant pyroxene chemistries; Magnya's pyroxenes contain ∼10 mol% less Fs than Vesta's pyroxenes. This suggests that Magnya originated from a parent body other than 4 Vesta and that its progenitor formed in a more chemically reduced region of the solar nebula within the asteroid belt.
Surface composition of near-Earth Asteroid (4179) Toutatis is consistent with an undifferentiated L-chondrite composition. This is inconsistent with early observations that suggested high pyroxene ...iron content and a differentiated body.
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