Planetary and Space Science最新文献

The spatial distribution of oxide abundances and Mg# (Mg/(Mg + Fe)) on the lunar surface is of great significance for in-depth understanding the origin and evolution of the Moon. China's Chang’E−5 (CE-5) mission returned young lunar soils for the first time, providing a new ground truth for the inversion of oxide abundances. In this study, the relationship between multi-source remote sensing data (including Chang’E−1 Interference Imaging Spectrometer (CE-1 IIM) data and the new global Christiansen feature (CF) product, named IIM-CF data), and the abundances of six oxides (FeO, TiO₂, MgO, SiO₂, Al₂O₃ and CaO) measured at 40 lunar sampling sites including CE-5 were analyzed. The use of IIM-CF data as the input features of the selected inversion models for obtaining the abundances of oxides, and the oxide abundances measured at the 40 sampling sites were used as the ground truth. The models selected for this investigation contain three typical algorithms − random forest (RF), extreme gradient boosting (XGBoost) and partial least squares regression (PLSR), and a new method integrates RF, XGBoost and PLSR together named RXP was developed in this study. The modeling results of the abundances of the six oxides derived from the above four algorithms show that the RXP algorithm outperforms the other three algorithms. The distributions of the six oxides and Mg# on the lunar surface covering the range from 70° N to 70° S (70° N/S) with a resolution of about 200 m/pixel were generated using the proposed RXP algorithm. Our results indicate that, compared with the result of a single data source, the use of IIM-CF data improved the accuracy of the modeling of oxide abundances and Mg#. It is expected that the CE-5 samples can bring additional references to the studies of the inversion for the oxides of the lunar surface and deepen our understanding over this issue.

In this study, we characterize the mineralogy and microbiology of a suite of samples from the Bagno dell’Acqua alkaline (pH ≥ 9) lake in Pantelleria, Italy. The aim of the present characterization is the assessment of the lake as a Martian analog site. Nineteen samples were characterized by a combination of VNIR reflectance spectroscopy, micro-Raman (μ-Raman) spectroscopy, and fluorescence microscopy. In addition, DNA extraction was performed on three selected samples to identify the bacteria phyla and to quantify their abundance. The samples were collected as push cores inside the lake and as loose sediments taken along the eastern and southeastern lake's shore. The samples underwent three thermal cycles (between 343 K and 473 K) to remove excess water and organic matter. The VNIR spectra were measured on each sample after each thermal cycle to check the variation of the spectral features as a function of thermal treatment. The mineralogical content of our push core samples is dominated by the presence of Mg-smectite clays always associated with the remanence of K-feldspars and Ca-carbonates while in the sediments we observe also additional minor phases like pyroxene (aegirine NaFe³⁺Si₂O₆), hematite (Fe₂O₃), anatase (TiO₂), and volcanic glass. Two organic phases were detected by μ-Raman spectroscopy. One phase was attributable to carotenoids, in line with the high abundance of Bacterial Phyla that can synthesize these molecules. The second phase appeared to be visually indistinguishable from the inorganic matrix and is therefore attributed to EPS (Extracellular Polymeric Substances) forming a biofilm and extensively observed by fluorescent microscopy. The peculiar chemistry of the waters, the presence of Mg-smectite in the sediments of Lake Bagno dell’Acqua associated with Ca-carbonates and sediments derived by biological activity makes Lake Bagno dell’Acqua a very interesting and promising Martian analog site.

This study presents results from five months of meteor observations that included simultaneous and nearby very low frequency (VLF) wave detections. We explore the plausibility of VLF emissions from meteors resulting in the documented phenomena of simultaneous optical and audio signatures with meteor events. Most previous attempts to observe VLF emissions from meteors have been limited in duration and/or in area covered during observations. With the extended duration and an observational network of three cameras and two VLF receivers across Colorado, an exhaustive approach was taken to detect meteor VLF emissions. The $\sim$650 events collected were closely inspected for any signs of emissions, with an emphasis on brighter meteors and fireballs. The VLF data was filtered using interference mitigation techniques to eliminate spurious signals that could obscure the VLF signals of interest. By comparing the VLF spectral content at the time of meteors and during control times, we search for very small changes in the signal that would be statistically correlated with meteor observation times. Despite these efforts, no VLF emissions have been detected that cannot be attributed to other sources. Most commonly, lightning-generated sferics coincident with the time of meteor events lead to false attributions to meteors.

The development of lunar habitat using lunar regolith is a captivating research area for constructing lunar bases, especially after the discovery of polar ice, and molecular water on the lunar south pole. The aim of this research is to synthesize a robust lunar regolith geopolymer by fine-tuning the concentration and ratios of alkaline activators while implementing curing under lunar positive thermal regime. The geopolymer was synthesized containing lunar highlands simulant (LHS-1) and mare regolith simulant (LMS-1) at the lowest water content using sodium (Na) and potassium (K) based alkaline activators emulating positive temperature regime collected by Diviner Lunar Radiometer Experiment (DLRE). The maximum compressive strength of 41.23 MPa was achieved for highlands regolith simulant-based geopolymer containing a Na-activator with the lowest water-to-precursor ratio of 0.23. The surplus alkali cations in the geopolymer paste matrix resulted in the formation of carbonation products after reacting with atmospheric carbon dioxide. K-activator geopolymer resulted in Kalicinite which has lower thermal stability and dissolution in water, whereas sodium carbonate formed in Na-activator-based geopolymer engrained and embedded precursor particles alongside sodium-calcium aluminosilicate hydrate (N-(C)-A-S-H) gel forming more densified microstructure. Conclusively, lunar regolith geopolymer has the potential for the construction of lunar habitat. However, this study recommends synthesizing geopolymer in vacuum conditions, emulating freeze-thaw cycles for a more precise estimation of microstructural developments and evaluating other critical properties.

The reflectance spectra of synthetic oldhamite (CaS), synthetic enstatite (Mg₂Si₂O₆), and their mixtures have been studied in the spectral range from 0.3 μm to 16 μm. The spectrum of enstatite is very bright, with a steep slope in the ultraviolet (UV) and an almost neutral slope in the visible (VIS) and near-infrared (NIR). The mid-infrared (MIR) region is characterized by the Christiansen feature, Reststrahlen bands and the Transparency feature. The oldhamite spectrum shows a red slope in the UV and VIS and an absorption band at 0.41 μm. The absorption band has a relative depth of 11.4%. In the MIR, the oldhamite spectrum is much brighter than the enstatite spectrum and shows several broad absorption bands. The spectra of the mixtures show an intermediate behavior between the two endmembers. The absorption band at 0.41 μm is visible in the spectra of all mixtures, even in the spectrum of the mixture with only 1 vol% oldhamite. In the MIR, the spectra of the mixtures with ≤10 vol% oldhamite are very similar to the spectrum of pure enstatite. Changes in the spectral characteristics such as reflectance or band depths do not follow simple linear trends but show two distinct trends: One for mixtures with ≤10 vol% oldhamite and one for mixtures with ≥20 vol% oldhamite. Changes occur significantly faster in the spectra of mixtures with ≤10 vol% than in those with ≥20 vol% oldhamite.

Reflectance spectra of the E[II]-type asteroid 2867 Šteins are flat and almost featureless but show an absorption band at 0.49 μm, which is attributed to oldhamite. Comparison of the laboratory spectra in the VIS and MIR with spectra of Šteins gives an upper limit for the oldhamite content on its surface of 40 %vol. Hence, Šteins probably consists of aubrite-like material with virtually FeO-free enstatite as the major constituent and an oldhamite abundance of <40 vol%. Šteins and other E[II]-type asteroids likely formed through igneous processes on a larger now destroyed body, where an immiscible CaS-melt formed within a silicate melt.

The surface of Mercury is also linked to FeO-poor silicates like enstatite. Oldhamite and other sulfides are linked to the formation of hollows on Mercury. Mixtures of enstatite and oldhamite could therefore serve as suitable model analog for the surface of Mercury. Contrasting trends at ∼7–8.5 μm in the MIR reflectance spectra of oldhamite and enstatite could be used as an indicator for the presence of oldhamite in spectral data that will be collected by the MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer) instrument onboard the ESA/JAXA BepiColombo mission to Mercury.

A comet flyby, like the one planned for ESA’s Comet Interceptor mission, places stringent requirements on spacecraft resources. To plan the time line of in situ plasma and neutral gas observations during the flyby, the size of the comet magnetosphere and neutral coma must be estimated well. For given solar irradiance and solar wind conditions, comet composition, and neutral gas expansion speed, the size of gas coma and magnetosphere during the flyby can be estimated from the gas production rate and the flyby geometry. Combined with flyby velocity, the time spent in these regions can be inferred and a data acquisition plan can be elaborated for each instrument, compatible with the limited data storage capacity. The sizes of magnetosphere and gas coma are found from a statistical analysis based on the probability distributions of gas production rate, flyby velocity, and solar wind conditions. The size of the magnetosphere as measured by bow shock standoff distance is $10^5$–$10^6$  km near 1 au in the unlikely case of a Halley-type target comet, down to a nonexistent bow shock for targets with low activity. This translates into durations up to $10^3$–$10^4$ seconds. These estimates can be narrowed down when a target is identified far from the Sun, and even more so as its activity can be predicted more reliably closer to the Sun. Plasma and neutral gas instruments on the Comet Interceptor main spacecraft can monitor the entire flyby by using an adaptive data acquisition strategy in the context of a record-and-playback scenario. For probes released from the main spacecraft, the inter-satellite communication link limits the data return. For a slow flyby of an active comet, the probes may not yet be released during the inbound bow shock crossing.

Atira Mons is a large (∼300,000 km²) low-relief (1.8 km) shield volcano, with individual flows extending up to ∼700 km from the central caldera. It is located about 3000 km NW from the major plume center Beta Regio. Detailed mapping of the flows (at 1:500,000 scale, 10x more detailed than previous mapping) has identified fifty-three flow units which are grouped into eleven packages. Flow units are distinguished based on radar brightness, topography, morphology, continuity, structural modification, and sources, while flow packages group flows with clear stratigraphic relationship affinity.

Cross-cutting relationships indicate a complex and multi-episodic eruption history with provisional identification of six mapped stages. The most voluminous flows are concentrated in the early stages, while the younger pulses, with a few exceptions, are shorter and less voluminous. A central caldera hosts the youngest volcanism with flows breaching its eastern side. Multiple stages of caldera collapse are indicated.

The volume of the volcano is estimated using various methods and yields values range from ∼47,000 to ∼270,000 km³. The larger estimates are consistent with that of the magma volume of Large Igneous Provinces (LIP) on Earth. An appropriate terrestrial analogue is the Benham Rise Oceanic LIP in the western margin of the Philippine Sea, and particularly the Apolaki Caldera, which is the world's largest known basaltic caldera with a diameter of ∼150 km.

We present a newly developed method which combines the nonlinear spectral mixing model of Shkuratov et al. (1999) with a machine learning algorithm to map the lunar regolith composition using spectral data. The new method performs orders of magnitude faster than the traditionally used numerical optimization approaches, allowing the mapping of regolith properties (including mineralogical composition, average grain size and optical maturity) over large areas of the lunar surface. A new set of basic mineral spectra of the lunar soil for using with spectral mixing models is proposed. Used together with the nonlinear mixing model (Shkuratov et al., 1999), the set is able to describes Chandrayaan-1 M³ instrument spectra collected from test areas which includes the Shapley crater with its surroundings containing mare and highland terrains well. The new set includes a virtual “gray component” with a “flat” (constant) spectrum, accounting for the factors that change general surface albedo, such as spectrally neutral components (e.g., agglutinate glasses), errors in the photometric reduction, uncertainties in estimations of lunar regolith porosity q and the mean grain size S of the basic minerals. The proposed new method takes into account the influence of space weathering and nonlinear correlation between the compositional and spectral parameters of the lunar soils delivering values for the optical properties and mineralogical abundance determination of the lunar regolith which are compatible with the results found from lunar samples measurements in the laboratory. The proposed approach can be used for analyzing spectral observations not only of the lunar surface but also for other surfaces with are covered by regolith.

The paper focuses on the influence of the optical properties of Martian surface minerals on remotely detected gaseous components of the Martian atmosphere, when the spectrometer receives a combined signal from the Martian soil and atmosphere. Our considerations are primarily concerned with the detectability of methane, but the problem may also apply to other trace gases. Detections of methane in the Martian atmosphere have been reported from Mars Express (orbiting Mars), the Curiosity rover on the Martian surface, and from Earth. Its presence in the Martian atmosphere is being questioned today. The reason for these doubts is that both spectrometers onboard ExoMars Trace Gas Orbiter have not yet detected any methane in the Martian atmosphere using the very sensitive solar occultation method. The solar occultation method is unable to probe the lowest layers of the atmosphere at mid-latitudes, and so, its presence in this part of the atmosphere is assumed to be due to its possible source in the ground, as suggested by some works.

This paper considers whether the spectral characteristics of the soil may hinder the remote detection of methane. One of the examples discussed in the article relates to the possible observation of methane over mineralogical surfaces that may be the source of this gas. The examples of other surface mineralogical compositions are also discussed. The series of numerical simulations carried out in the region of the strong methane absorption band and the examples where the optical properties of the surface change the shape and contrast of this absorption band are shown. The codes used provide estimates of the spectral reflectance/emittance and total radiance of the Martian surface and atmosphere in the mid-infrared spectral region. The surface covered by dust was described by the reflectance and emittance calculated from n,k using Mie and Hapke theories or known from laboratory measurements. The different concentrations of atmospheric trace gases were taken into account.