Planetary and Space Science最新文献

Upcoming large multiwavelength photometric surveys will provide a leap in our understanding of small body populations, among other fields of modern astrophysics. Serendipitous observations of small bodies in different orbital locations allow us to study diverse phenomena related to how their surfaces scatter solar light.

In particular, multiple observations of the same object in different epochs permit us to construct their phase curves to obtain absolute magnitudes and phase coefficients. In this work, we tackle a series of long-used relationships associating these phase coefficients with the taxa of small bodies and suggest that some may need to be revised in the light of large-number statistics.

Many processes have been identified in the Martian subsurface which may produce or release methane that eventually can be emitted into the atmosphere. Given the wide range of isotopic values for source carbon reported on Mars and the importance of atmospheric methane isotopologues as a tracer for subsurface processes, it is critical to quantify the level of isotopic fractionation that can occur during subsurface transport. On Earth, isotopic fractionation occurs when methane transport is dominated by Knudsen diffusion through small pores. However, unlike the Earth, on Mars the low atmospheric pressure and commensurate longer mean free path suggest that most subsurface transport of methane occurs in the Knudsen regime, amplifying this effect. Here, we report on simulations of diffusion through the martian subsurface and report on the level of fractionation that would be expected under two end-member scenarios. For Interplanetary Dust Particles (IDPs) incorporated in near-surface sediments in which methane is released quickly upon generation, atmospheric emissions of methane are expected to be representative of the reservoir isotopic ratio. However, for deeper sources in which methane accumulates as trapped gas, subsurface transport will result in depletions of ¹³CH₄ compared to reservoir concentrations by approximately −31‰. Over time, both the reservoir and the emitted gas will evolve to become isotopically enriched in ¹³CH₄ compared to a standard of constant isotopic ratio. This necessitates temporal measurements of emitted methane to understand the δ¹³C of the reservoir and depth of the release, preferably with hourly or better frequency. Finally, a seasonal cycle in δ¹³C with an amplitude of 5.3‰ is expected with adsorption acting to create small temporary reservoirs that are filled and emptied over the year by the subsurface thermal wave. This effect may provide a way to probe near-surface thermophysical properties.

Water ice is distributed on the surface and in the subsurface of the Moon, as confirmed by observational data, and predicted by several numerical models. In this respect, the direct search for lunar water is the main objective of the ESA’s PROSPECT package, that aims to analyze a region of interest at the lunar South Pole. PROSPECT, originally on the Russian Luna 27, is now on the CLPS (Commercial Lunar Provider Service) “CP” 22 mission. In this work, we applied our 3-D FEM thermophysical model to investigate the landing site selected for the CP 22 mission, which is centred at −84.496°S, 31.588°E, and located on the Leibnitz Plateau and within an area of high elevation. The purpose of our model is to investigate regions of interest (ROI) on the lunar surface by working with the real topography at the scale of 5 m, by using the DEM (Digital Elevation Model) of the region. Since the lunar surface is characterized by topographic variations such as craters or boulders, a 3-D model is preferable over a 1-D numerical model. We produced temperature maps of the surface and 1-D temperature vs depth, as well as we produced illumination maps, computing also the indirect contribution. These simulations will provide a complete thermophysical vision of the landing site, offering a theoretical support to the researchers and engineers of the CP 22 mission, and of future lunar missions. In addition, this model can be applied to every site of the Moon surface and subsurface and, in general, to any airless body of the Solar System.

The Visual Monitoring Camera (VMC) is a small imaging instrument onboard Mars Express with a field of view of ∼40°x30°. The camera was initially intended to provide visual confirmation of the separation of the Beagle 2 lander and has similar technical specifications to a typical webcam of the 2000s. In 2007, a few years after the end of its original mission, VMC was turned on again to obtain full-disk images of Mars to be used for outreach purposes. As VMC obtained more images, the scientific potential of the camera became evident, and in 2018 the camera was given an upgraded status of a new scientific instrument, with science goals in the field of Martian atmosphere meteorology. The wide Field of View of the camera combined with the orbit of Mars Express enable the acquisition of full-disk images of the planet showing different local times, which for a long time has been rare among orbital missions around Mars. The small data volume of images also allows videos that show the atmospheric dynamics of dust and cloud systems to be obtained. This paper is intended to be the new reference paper for VMC as a scientific instrument, and thus provides an overview of the updated procedures to plan, command and execute science observations of the Martian atmosphere. These observations produce valuable science data that is calibrated and distributed to the community for scientific use.

The multiple-layered ejecta surrounding crater Kotka (east of Elysium Mons) are studied using imagery and physical modelling. This particular crater was chosen not only because its ejecta are well preserved, but more importantly because the impact area is surrounded by mounds, which provide a means of determining the velocity of the ejecta based on run-up criteria. If the ejecta passed over a mound of a certain height, the velocity was greater than that necessary to rise up that height, while the presence of a shadow beyond the mound indicates a velocity lower than that limit. Top ejecta flow velocities were found to vary between 25 m/s and 80 m/s. Velocities are also determined based on the length of the jump against craters rims, a criterion that provides an estimate of the velocity, rather than a limit, and are found to be compatible with those estimated with run-up criteria. We find that a first train of ejecta travelling at high velocity was capable of overcoming many mounds. A peculiar rampart often visible at the foot of many of the mounds is interpreted as a frozen hydraulic jump indicating a phase in which the ejecta were about to stop.

The velocity of the ejecta was found to decrease with distance from the rim but not as fast as a constant friction model would suggest, indicating effective friction that increases with distance, and more complex rheology than pure frictional behavior. The velocities indicate a rheology for the fluidized ejecta in which the debris material was completely fluidized, to the point that the friction coefficient decreased by one to two orders of magnitude compared to the one of fragmented rock. Our conceptual model is that the ejecta material initially contained a large amount of solid ice that was fluidized and vaporized by the impact. The chains of pits visible in the ejecta, interpreted as fossilized bubbles of volatiles released through the hot fluidized material, confirm that high temperatures were reached during impact, as also indicated by analytical estimates. Fluidization altered the rheology of the ejecta in a way that has yet to be understood.

Water on the Moon has received increasing attention due to its importance in planetary science and the utilization of space resources. Future lunar rover missions are poised to conduct explorations, specifically focusing on locating water. Neutron spectroscopy is a powerful technique for estimating subsurface water content. In this study, lunar surface neutrons induced by galactic cosmic rays were investigated through Monte Carlo simulation. This effort aims to yield insights pertinent to in-situ water search explorations utilizing neutron spectrometers. The sensitivity of the leakage neutron intensity to the depth profile of subsurface water within the top 1.5 m soil was obtained via calculations based on a lunar surface model, featuring a localized concentration of water-rich soil. Computational outcomes underscore the potential of neutron observations to provide data on the depth profile of subsurface water under specific circumstances. Notably, in scenarios where a thin and shallow water-rich layer, approximately $\lesssim$20 cm thick and located $\lesssim$50 cm deep, is assumable within lunar soil of density 1.6 g/cm³, a combination of thermal, epithermal, and fast neutron measurements enables concurrent estimation of water abundance and depth. To accurately understand the subsurface water abundance and depth across exploration areas along the rover’s path, a comprehensive assessment of leakage neutrons in a wide energy range becomes indispensable.

In the actively evolving research of Mars in recent decades, a special place is occupied by landers and rovers. The diversity of landscapes and soils on Mars, characteristic of terrestrial planets with an atmosphere, makes the development of soil simulators relevant for each new type of terrain in the area of a potential landing site. In the article, based on a comprehensive analysis of the physical and mechanical properties of soils at previous landing sites and a geomorphological analysis of the Oxia Planum plain, the main requirements for the properties of Martian soil analog at the landing site of the ExoMars Rosalind Franklin Mission (RFM) were determined. Readily available technogenic and natural materials have been selected and experimentally justified as components for creating a Martian soil analogue. A methodology for creating the soil analog is presented, and its physical and mechanical properties are measured. The developed Martian soil analog VI-M1 is actively used for large-scale natural experiments, including drop tests of spacecraft in the ExoMars series.

The polar motion of Mars is defined as the movement of the rotation axis with respect to a body-fixed frame tied to the crust of the planet. It is composed of forced motion at annual and sub-annual frequencies caused by the seasonal mass redistribution, formation of the polar ice caps and angular momentum variations of the atmosphere, and of the free mode called the Chandler wobble.

Radio-tracking data from landers offers the most suitable means to measure the rotation of Mars, including its polar motion. The latter, however, has not yet been achieved using lander data alone. In this study, we assess the uncertainties associated with Mars polar motion estimation using Direct-To-Earth Doppler, range and Same-Beam Interferometry (SBI) observables between multiple landers on the surface of Mars. We evaluate the improvement enabled by combining data from multiple landers with respect to one-lander scenarios, and identify the optimal mission architectures for polar motion estimation by considering the influence of respective mission parameters on the estimation uncertainty. In particular, we consider the effects of absolute and relative locations of the landers and of mission scheduling. We re-evaluate the possibility of estimating the polar motion using data from landers in proximity to the equator, and apply our considerations to simulated data consistent in number and accuracy with that collected by past Martian missions. We notice and explain a strong longitude dependence of the formal errors when the polar motion parameters are estimated concurrently with the seasonal spin variation parameters, making it impossible to properly determine all components of polar motion with a single lander regardless of its location. However, the use of two or more landers in optimal locations with respect to each other eliminates those limitations. We evaluate the influence of latitudinal and longitudinal separation on polar motion determination in such cases. In particular, we are able to determine polar motion well even in cases where the longitudes of the two landers make determination from each single lander impossible.

The Chandrayaan-3 (CH3) Vikram lander presents an unique opportunity to study the radar scattering behavior of the landing site as well as human-made dihedral structure on the lunar surface. This opportunity is made possible by the Dual-Frequency Synthetic Aperture Radar (DFSAR) sensor onboard the Chandrayaan-2 orbiter, which has the highest resolution and polarimetric capabilities compared to any planetary SAR sensor. To explore this, we utilized DFSAR to capture high-resolution images of the CH3 landing site during pre-landing and post-landing condition, with a pixel spacing as fine as 1 m, in a hybrid-pol mode. The landing site exhibits dominant volume and even-bounce radar scattering behavior similar to an ideal dihedral geometry. Furthermore, we observed an exceptionally high Circular Polarization Ratio value at the landing site (1.99 ± 0.30), a rarity among natural features on the lunar surface. Besides, the landing site is characterized by enhanced average dielectric constant value (5.76 ± 3.11). The post-landing DFSAR image reveals a 177 m² area, surrounding the CH3 landing location, characterized by high CPR and elevated even bounce and volume scattering. The drastic enhancement of the average CPR value (7-times), dielectric value (2-times), even bounce and volume scattering in the landing site, in comparison with the pre-landing DFSAR observation, is due to presence of lander module and disturbance in the regolith structure in the landing area. The polarimetric characteristics of the landing site distinguish it from the major natural features on the lunar surface, such as regolith, debris flow, and impact ejecta. This investigation is of utmost importance as it emphasizes the effectiveness of high-resolution DFSAR acquisitions for evaluating the polarimetric behavior of small-scale features, which can be invaluable for characterizing landing sites in upcoming missions.