Planetary and Space Science最新文献

Apollo 17 astronauts spent three days exploring the Taurus Littrow Valley on the Moon in 1972. During their third Extravehicular Activity, they spent more than 1 h at Station 6, a geologic waypoint consisting of three big and two small fragments of a boulder that rolled down the North massif. We have used all the available scanned digital Apollo photos taken by the astronauts at this Station 6 to compute a comprehensive 3D model of the explored area. We used Structure From Motion photogrammetry to automatically derive the position of each of the 154 available images using their overlap. All images were aligned in a single photogrammetric project, which allows on one hand to automatically visualize the astronaut positions during their investigations, and on the other hand to reconstruct in 3D the three main pieces of boulders, therefore constraining their respective size and orientation. In addition to the boulders, we show that the 3D reconstruction by photogrammetry can also be applied to the rock samples taken from the boulders themselves. These samples were systematically photographed from multiple angles at the LPI during the 70s when brought back to Earth. For the reconstruction, we used scanned archived images representing 16 stereoscopic pairs, to compute 3D models of samples 76015, 76215, 76315 and 76275. These models might play a role in preservation as some of the samples, latter sawed for analysis, do not exist anymore in their pristine form. 3D models of the boulders and rock samples can then be manipulated and visualized on a web-based platform. 3D models have also been integrated into a virtual reality scene in order to provide the possibility to investigate their properties at full scale in an immersive and collaborative way. The knowledge of the samples position and orientation directly in their context might for example provide additional constrains to better understand processes such as the space weathering alteration due to micrometeorite impacts and solar wind particle. 3D photogrammetric reconstructions using images taken by rovers and/or astronauts might be one of the basic techniques to consider in forthcoming lunar missions in order to maximize their scientific, educational and outreach return.

The paper presents the results of positional observations of nine near-Sun asteroids with the Zeiss-2000 telescope at the Center for Collective Use “Terskol Observatory” during 2020–2023. It demonstrates that, under favorable weather conditions, it is possible to obtain observations of asteroids with observed magnitudes up to 22. Particular attention is paid to the objects (399457) 2002 PD43 and 2008 MG1. We managed to obtain observations of (399457) 2002 PD43 at an observed magnitude of 21.6^m, making our observations the first of the summer 2022 opposition. The results of the orbit fitting and the study of the probabilistic orbital evolution of 2008 MG1 are considered separately, since the observations at the Terskol observatory significantly extend its arc length and reduce the orbit uncertainty.

The Perseverance rover of NASA’s Mars 2020 mission carries a pressure sensor (PS) provided by the Finnish Meteorological Institute (FMI). The sensor belongs to the Mars Environmental Dynamics Analyzer (MEDA), a set of environmental sensors designed to characterize the near-surface atmospheric conditions. MEDA PS is based on the same Vaisala sensor and measurement technology as the pressure sensor of the Curiosity rover, but utilizes newer-generation sensor heads. The sensor has been calibrated in the pressure range of 0–14 hPa and temperature range from −45 to ＋55 °C. The calibration is based on tests performed in FMI’s pressure calibration laboratory, as well as measurements done after integration to MEDA and the rover. Since February 2021, MEDA PS has operated flawlessly on board Perseverance, delivering regular measurements of the local atmospheric pressure in Jezero crater. According to the evaluation based on the first 530 sols, MEDA PS is found to provide high-quality data with performance meeting expectations.

Results of NASA's Dawn mission indicate that Ceres, the biggest object in the main asteroid belt, may be geologically active because it shows changes in its morphology that might have happened in geologically recent times. Juling is a ∼2.5 Ma old, 20-km diameter impact crater on this dwarf planet, which has an extensive ejecta blanket of spectrally bright bluish material and water ice exposures on its steep northern inner wall. The crater floor is dominated by a spectrally reddish material, which is distinct from other surface types in this region. No other crater of Juling's size on Ceres, shows such a reddish floor. In addition, the floor has a complex morphology characterized by lobate flows and indications of a north-south directed mass wasting possibly leading to the elongated, ∼16 km long and several hundred-meter-high central structure. Here we describe the characteristics of the material that constitutes the floor, and we present a geological map of the crater, using the Framing Camera (FC) imagery. From the analysis of data acquired by the Visible and Infrared Spectrometer (VIR), we did not find evidence for the presence of organic rich materials in Juling at the available data resolution. The spectrum of the floor material seems to be a combination of mineralogy and physical properties of the regolith. Our findings suggest that the processes leading to the reddish material and the peculiar morphology of the crater floor, must have occurred after the formation of Juling crater.

Appreciable amounts of hydrogen-bearing compounds have been detected within the lunar polar regions. Estimating the effect of the presence of water ice on surface topographic roughness is important for future exploration and activities in the vicinity of the lunar pole. To investigate this issue, we analyzed the correlations between water equivalent hydrogen in the top 1-m surface layer and topographic roughness of lunar south polar regions. The results show that water ice probably plays an important role in the surface roughness at the hectometer scale, and might has a suppressive effect on surface roughness. In the detailed analysis, most the surface roughness at the floor of Shoemaker, Faustini, Slater and Sverdrup shows a decreasing trend with increasing water equivalent hydrogen at different decreasing slopes; Haworth shows slightly increasing trend, contrary to the trend of other studied craters. These observations may be related to small-scale topographic features at the surface and/or subtle changes in surface and subsurface WEH, which in turn affect the roughness characteristics in detail.

A series of numerical simulations of terrestrial mantle convection with temperature-dependent viscosity in a three-dimensional spherical geometry was performed to investigate the thermal structure of the mantle interior and the mechanical condition of the lithosphere. The common “sluggish-lid” convection regime has the thermal structure of the mantle interior with a slowly mobile lid under a moderately temperature-dependent viscosity of mantle rocks, whereas the “stagnant-lid” convection regime has a convection pattern in which the entire surface is covered by a highly viscous lid due to the strongly temperature-dependent viscosity. This study focused not only on the thermal structure of the mantle but also on the mechanical conditions in the lithosphere on an intermediate, transitional convection regime between these end-member convections both under the standard- and the extended-Boussinesq approximations. In this “quasi-stagnant-lid” convection regime, the entire surface of the planet is covered by a highly viscous stagnant-lid that moves slowly, whereas the mantle interior is dominated by a long-wavelength (i.e., degree-one) thermal structure. The stress regime analyses revealed that the strike-slip regime is highly restricted spatially in the lid. If the constitutive laws allow the formation of faults in the future numerical model, the time-dependent formation of weak faults that can initiate plate tectonics may differ among the three convection regimes (i.e., degree-one, quasi-stagnant-lid, and stagnant-lid convection regimes). The range of viscosity contrast of the lid required to realize the “quasi-stagnant-lid” convection regime in the model under the extended-Boussinesq approximation was wider than under the standard Boussinesq approximation, because the adiabatic heating of the mantle increased the mantle temperature with the depth and enhanced the formation of stagnant-lid owing to the strong mechanical decoupling between the cold lid and the underlying hot mantle.

The April Lyrid meteor shower is the oldest meteor shower ever recorded continuously throughout history, dating as far back as 687 BC. Before the 20th century, historical sources only provided reports of two years of strong activity and up to nine possible additional events. Currently, the shower has low activity, but it has had significant episodes that, during the 20th century, seem to repeat at time intervals that are multiples of 12yr or 60 yr. Earlier outbursts may have also occurred with a frequency consistent with this period. Outbursts of activity are also known in other meteor showers. The classical explanation that they are correlated to the close proximity of the parent comet to the Earth was proven wrong in the last years of the 20th century and this is also clear in the case of the April Lyrids, whose parent comet is C/1861 G1 (Thatcher), with an orbital period of about 400 yr. Our previous research has led us to compile an additional list of possible April Lyrids in the last 2000 years. This paper has two objectives. First, to present the list of possible Lyrids that we have compiled that would significantly increase the number of historical observations considered to date. Secondly, to study if the historical data fit well with the main theories and recent studies concerning the Lyrids.

In recent decades, the use of optical detection systems for meteor studies has increased dramatically, resulting in huge amounts of data being analyzed. Automated meteor detection tools are essential for studying the continuous meteoroid incoming flux, recovering fresh meteorites, and achieving a better understanding of our Solar System. Concerning meteor detection, distinguishing false positives between meteor and non-meteor images has traditionally been performed by hand, which is significantly time-consuming. To address this issue, we developed a fully automated pipeline that uses Convolutional Neural Networks (CNNs) to classify candidate meteor detections. Our new method is able to detect meteors even in images that contain static elements such as clouds, the Moon, and buildings. To accurately locate the meteor within each frame, we employ the Gradient-weighted Class Activation Mapping (Grad-CAM) technique. This method facilitates the identification of the region of interest by multiplying the activations from the last convolutional layer with the average of the gradients across the feature map of that layer. By combining these findings with the activation map derived from the first convolutional layer, we effectively pinpoint the most probable pixel location of the meteor. We trained and evaluated our model on a large dataset collected by the Spanish Meteor Network (SPMN) and achieved a precision of 98%. Our new methodology presented here has the potential to reduce the workload of meteor scientists and station operators and improve the accuracy of meteor tracking and classification.

We computed the ablation of different spherical artificial meteoroids entering from a low-Earth orbit in the context of the AllBert EinStein mission. AllBert EinStein is intended to reenter spheres of known size and material into the atmosphere to determine the percentage of kinetic energy converted to light. This paper models the reentry to predict magnitude curves for the different initial conditions. An emphasis is placed on determining the difference between the single body ablation model and ESA’s reentry software SCARAB. It is also shown how the CFD simulations can work in synergy with SCARAB results to increase detail in the airflow regime around. Our study shows that with few fixes the meteor method replicates with good accuracy the SCARAB results for different artificial meteoroids, showing the validity of both tools.

PRAIA – Package for the Reduction of Astronomical Images Automatically – is a suite of astrometric and photometric tasks designed to cope with huge amounts of heterogeneous observations with fast processing, no human intervention, minimum parameterization and yet maximum possible accuracy and precision. It is the main tool used to analyse astronomical observations by an international collaboration involving Brazilian, French and Spanish researchers under the Lucky Star umbrella for Solar System studies. In this paper, we focus on the astrometric concepts underneath PRAIA, used in reference system works, natural satellite and NEA astrometry for dynamical and ephemeris studies, and lately for the precise prediction of stellar occultations by planetary satellites, dwarf-planets, TNOs, Centaurs and Trojan asteroids. We highlight novelties developed by us and never reported before in the literature, which significantly enhance astrometry precision and automation. Such as the robust object detection and aperture characterization (BOIA), which explains the long standing empirical photometry/astrometry axiom that recommends using apertures with 2 – 3 $\sigma$ (Gaussian width) radius. We give examples showing the astrometry performance, discuss the advantages of PRAIA over other astrometry packages and comment about future planed astrometry implementations. PRAIA codes and input files are publicly available for the first time at: https://ov.ufrj.br/en/PRAIA/. PRAIA astrometry is useful for Solar System as well as astrophysical observations.