Planetary and Space Science最新文献

A climate model is developed for Earth climate history simulations or snapshots of possible conditions on Earthlike exoplanets. It includes estimates for shortwave and longwave optical thickness based on data from Venus, Earth, and Mars; expressions for atmospheric shortwave absorption and surface convective heat loss; climate feedbacks due to water vapor, ice-albedo, clouds, and lapse rate; and a new model for planetary and surface albedo which takes account of surface cover, Rayleigh scattering, and differing wavelength fractions due to primary spectral class. While somewhat complex, it is still orders of magnitude faster than full-spectrum methods or radiative-convective convergence. The model can be modified for use with tidally locked planets, and is here applied to Proxima Centauri b as an example.

With the mission's completion, India became only the fourth nation in history to successfully perform a soft landing on the Moon and the first nation to land a spacecraft close to the lunar south pole. The purpose of the article is to present a comprehensive review of the Chandrayaan-3 mission (a sequel operation to Chandrayaan-2) to demonstrate complete capabilities in secure lunar landing and exploration on the Moon's surface. It is equipped with a Vikram lander and Pragyan rover. An in-depth review is carried out to discuss the findings of the Chandrayaan-3 mission. The goals of Chandrayaan-3's mission are: (a) to show a safe and soft landing on the surface of the Moon; (b) to showcase roving lunar rover technology; and (c) to carry out in-situ scientific research. The goals are achieved through the lander payloads, which include the Langmuir Probe (LP), Chandra's Surface Thermophysical Experiment (ChaSTE), Instrument for Lunar Seismic Activity (ILSA), and Chandra's Surface Thermophysical Experiment (ChaSTE) to measure thermal conductivity and temperature. For lunar laser-ranging investigations, the space agency NASA has provided a passive Laser Retroreflector Array. The Alpha Particle X-ray Spectrometer (APXS) and the Laser Induced Breakdown Spectroscope (LIBS) are rover payloads that were used to determine the elemental composition close to the landing site. The mission goals are highly accomplished with the successful hop experiment of Vikram on the Chandrayaan-3 mission! As ordered, it raised itself to a height of around 40 cm, turned on its engines, and then made a safe landing between 30 and 40 cm away. To put an end to the controversy, the study finishes with highlights on (a) the significant area of the southernmost polar region of the Moon with latitudes ranging from 60 to 90°S and (b) Shiv Shakti point (coordinates 69.373°S 32.319°E).

We use a customized radiative transfer model to show that sharp ($\sim$10 m resolution) images of the Venus surface can be achieved at night in spectral windows free of CO${}_2$ absorption found between 1.0 and $1.2\mu m$ using a camera at 47 km altitude, just below the planet’s optically thick clouds. This is in spite of the Rayleigh scattering by the dense but still semi-transparent lower atmosphere, and the potential for underlying hazes beneath the clouds. The thermal radiation transmitted directly to the camera forms images of spatially varying surface emissivity and/or temperature at the native sensor resolution, platform stability permitting and under reasonable seeing conditions. Near-isotropic Rayleigh scattering dominates in the $1.0\mu m$ window. Combined with near-Lambertian reflections off the base of the cloud layer, the diffuse light field builds up a background radiance from surface emission averaged spatially out to several 10s of km, i.e., beyond the camera’s field-of-view. At the longer wavelengths (1.1 and $1.18\mu m$ windows), the sub-cloud atmosphere itself partially absorbs (hence less direct light), and therefore weakly emits (hence more background light), but the rapidly decreasing Rayleigh scattering compensates and contrast is maintained. In all cases, we demonstrate that the directly-transmitted surface-leaving radiance from the native sensor resolution element ($\sim$10 m) is a significant fraction of the total radiance, and thus can be detected above the background light. Extending down to the 0.85 and $0.90\mu m$ spectral windows, there is less direct and more background due to the enhanced Rayleigh scattering, but the resulting reduction in contrast can be mitigated by co-adding the $\sim$10 m pixels. This technological advance will open a new era in Venusian geology by enabling discrimination between different surface materials at fine scales. Moreover, potentially active volcanism on our sister planet may be revealed by surface spots that are much hotter than their surroundings.

The surface of Mars preserves a variety of structural and geomorphic features such as wrinkle ridges, graben, lobate scarps, impact basins, paleochannels etc., which owe their origin to endogenic processes of deformation as well as meteorite impacts. Graben, which form in extensional stress regimes, are one of the most common structural features identified on these planetary bodies. Many graben are observed in the Margaritifer Terra, a Noachian (4.1 Ga to 3.7 Ga) highland terrain in the southern hemisphere of Mars; but a detailed structural study of these graben have not been carried out so far. The diverse geomorphology of these graben such as their orientation, planform and disposition make the region interesting for structural geological studies. With an aim to unveil the causes behind the formation of these graben, detailed morphometric analyses, estimation of maximum displacement of the faults, and extension across them (ranging between ∼0.3 and ∼0.8 km), as well as age estimation (minimum ∼1 Ga to maximum ∼3.8 Ga) and correlation with the stratigraphic units are carried out on eleven prominent graben in the Margaritifer Terra. The graben belong to two age clusters: 1) late Noachian–early Hesperian and 2) Amazonian. The age-depth correlation, proximity to chaos and floor-fractured craters, absence of any dominant geographic trend and presence of circular graben together indicate that the graben were formed due to dike emplacement in the area in two distinct phases separated by about 2 Ga. Older graben were formed above dike tops at greater depth (>50 km below the surface) while dikes below the younger graben reached shallower levels (∼4 km below the surface) below the surface. The intrusive activities are local to the Margaritifer Terra region and were possibly not caused by Tharsis and Valles Marineris related deformation.

The first discoveries of Interstellar Objects (ISOs), i.e., small bodies moving through our Solar System on high-speed hyperbolic orbits, occurred in 2017 and 2019, decades after ISOs were first predicted. The scientific value of ISOs is high, as they represent samples, most likely planetesimals, from other solar systems. A significant increase in the rate of ISO discoveries is expected in the late 2020s and in the 2030s owing to the advent of several new observing capabilities enabling more routine ISO detections. Here we investigate how a space mission to reconnoiter an ISO can be designed, including discussions of the scientific objectives and payload for such a mission, its unique mission design aspects, and some preliminary spacecraft and payload considerations, all in support of possible proposals to conduct such a mission in the 2030s.

Here we describe the design, prototyping, testing, and simulations that were conducted to demonstrate the technology for a concept of the next generation landed planetary spectral imager, the Europa Lander Stereo Spectral Imaging Experiment (ELSSIE). The concept was developed originally for a Europa Lander mission, but the design is applicable, with simplifications, to any ocean world of the outer solar system or to non-icy bodies, including Enceladus, the Moon, Mars, or the surface of Ceres. ELSSIE's design consists of two subassemblies. A Sensor melds a high-resolution, 20-filter, 0.4–3.65 μm, adjustable-focus multispectral stereo imager with a 0.8–3.6 μm point spectrometer, sharing a radiation-shielded single Teledyne H2RG 2048 × 2048 pixel focal plane array (FPA). Each camera includes two 6-position filter wheels with 5 filters and a blank position, providing 10 bandpasses for each of the 2 stereo eyes, and uses 700 × 700 pixels of the FPA. The point spectrometer uses a 6 ×350 pixel strip of the FPA. The Sensor provides stereo and imaging/spectroscopic measurements of reflected light from visible to medium wave-infrared (MWIR) wavelengths to characterize surface morphology, search for pyroclastic plumes, search for organics, identify salts and possible biominerals, characterize crystalline vs. amorphous ice and ice grain sizes, and map the distributions of key phases. In addition to addressing important geologic questions, these measurements support selection of a site for in situ sampling and analysis. A Data Processing Unit (DPU) performs mitigation of radiation that penetrates the shielding using sets of same-filter image frames or spectra of a single spot by removing image spatial pixels with radiation hits, and coadding the remainder for the same spatial pixel, improving signal-to-noise ratio (SNR). The DPU also performs onboard calibration of imager and spectrometer data, co-registration of multispectral images, and calculation of spectral index (“summary parameter”) images for efficient use of lander downlink. Co-registered multispectral image sets and spectra are retained onboard and can be downlinked upon query.

Our study is based on a photogeological analysis of the hill-shade images produced from the LOLA digital terrain models and on a stereometric analysis of LROC NAC images. Our results demonstrate that surface morphology of the permanently shadowed floor of crater Shoemaker is nearly identical to that of the regularly illuminated mare surface at the Lunokhod-2 working area and the surface of the highland plain of the Apollo-16 landing site, being dominated by populations of craters smaller than 1 km in diameters. Craters on the Shoemaker floor have approximately the same depth-to-diameter ratios as those within the Lunokhod-2 and Apollo-16 areas. The observed surface morphology of the Shoemaker floor is the result of meteorite bombardment like in other areas of the Moon. Within the permanently shadowed surface areas we detected no morphological peculiarities that could result from the absence of the diurnal temperature variations that excludes the temperature-related creep component of the downslope material movement. This probably means that in the areas with regular solar illumination, the role of the downslope movement of debris by thermally induced creep mechanisms is secondary compared to shaking by close and distant meteorite impacts and locally by moonquakes.

The mass distribution of fragments is an important characteristic that often needs to be defined for forward modelling the interaction of disrupted meteoroids and asteroids with the atmosphere, and which can be inferred to some extent by the distribution of meteorites that fell to the ground. In previous studies, we derived a formula for the mass distribution of fragments of a disrupted body assuming a power law for the distribution in a differential form, and applied this formula to describe the results of many impact experiments modelling fragmentation of asteroids in outer space. The formula represents the cumulative number of fragments as a function of the fragment mass normalized to the total mass, the mass fraction of the largest fragment and the power index, which is the only free parameter adjusted to best fit the analytical distribution to the empirical one. Here, we use the proposed formula to describe the mass distributions of recovered meteorites that fell to the ground after the passage and disruption of thirteen extraterrestrial objects in the atmosphere, as well as the mass distributions of fragments of meteorite samples disrupted in impact experiments. A comparison is made between the distributions of unevaporated fragments of bodies disrupted in the atmosphere and the distributions obtained after the disruption of bodies in experiments. Some regularities in meteorite distributions and the influence of the incompleteness of the available collection of meteorites on their mass distribution are discussed.

The magnetized supersonic solar wind, when flowing around planets, forms a magnetic barrier near the streamlined surface. The main feature of the magnetic barrier is that the magnetic pressure prevails over the plasma pressure. The Hall-MHD model is used to simulate the magnetic barrier in the case of solar wind flow around the atmosphere of Venus. The obtained numerical results are compared with an analytical approximation of the magnetic barrier thickness, which expresses the dependence of the magnetic barrier on solar wind parameters. Particular attention is paid to the physical reasons for the asymmetry of the magnetic barrier caused by the Hall effects, which are mainly concentrated in the boundary layer near the ionopause, where the electric current has a maximum strength. An additional source of asymmetry is also considered, which acts in the same direction and is associated with the influence of the normal component of the electric field on the specific behavior of new atmospheric ions. It is shown that solar wind protons are loaded by new atmospheric ions mainly in the $E_{+}$ hemisphere. In the case of more intense loading, the boundary of the magnetic barrier and the shock wave are located farther from the ionopause.