Planetary and Space Science最新文献

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.

This work investigates a novel signature for measuring the Ni/Fe ratio on the asteroid (16) Psyche that is robust against interference from large Solar Particle Events. NASA's Psyche mission launched on October 13th, 2023, and is headed to investigate this M-type asteroid. A primary science requirement for the Psyche gamma-ray spectrometer is to measure the absolute surface abundance of Ni and Fe. In particular, the Ni/Fe ratio will help test the hypothesis that (16) Psyche is a metal-rich body, possibly a remnant core from a failed planetesimal. However, Solar Particle Events can activate iron in the spacecraft, as well as the body of Psyche itself, disrupting the measurement of the surface abundance of iron for six months or more. Such an event happened during NASA's MESSENGER mission in orbit around Mercury on June 4, 2011, precluding further mapping of iron for the remainder of the mission. A similar event at Psyche could adversely affect mission science goals and/or prolong operation. Given the expected high abundance of Fe at Psyche, this paper proposes an alternative signature that relies on gamma rays from ⁵⁴Fe rather than ⁵⁶Fe. Although ⁵⁴Fe has a lower natural abundance than ⁵⁶Fe (5.8% vs 91.7%, respectively), ⁵⁴Fe is much less susceptible to interference from activation and would allow measurements of the surface abundance of iron to resume within days after a large Solar Particle Event. In addition, ⁵⁸Ni is shown not to be susceptible to interference from activation, thus making the ⁵⁸Ni/⁵⁴Fe ratio a robust alternative signature in the presence of Solar Particle Events.

High-accuracy wavelength calibration is critical for qualitative and quantitative spectroscopic measurements. Many spectrometers employed in planetary-exploration missions have onboard calibration sources, including standard lamps and calibration targets. However, such calibration sources are not always available because planetary missions, particularly landing missions, usually have limitations in size and mass. Thus, a wavelength calibration method without requiring hardware addition can be highly beneficial. In this study, we demonstrate a method for wavelength calibration using solar Fraunhofer lines observed in the reflectance spectra of planetary surfaces. Using a Raman spectrometer prototype developed for a Phobos rover, we measured the spectrum of the sunlight reflected from a spectral standard, manufactured to provide similar reflectance spectra to the surface of Phobos. We identified 35 Fraunhofer absorption lines in the wavelength range between 530 and 700 nm and utilized these features for the wavelength calibration of the spectrometer. This approach using Fraunhofer lines achieved good results (better than +0.04/−0.06 nm), comparable to the results achieved using a conventional Ne lamp. The wavelength accuracy corresponds to a wavenumber accuracy better than ±1.5 cm⁻¹ in the 0–4000 cm⁻¹ Raman shift (Stokes shift) range with a 532 nm excitation laser. This result enabled the estimation of the magnesium number (Mg#) of olivine, achieving a value more precise than 1.5% based on the Raman peak positions. In addition, we examined the number of solar Fraunhofer lines detectable at different wavelength resolutions by binning the solar spectrum acquired in this study. We found that more than 10 Fraunhofer lines could be detected as prominent absorption lines when the wavelength resolution is higher than 1 nm/pix (30 cm⁻¹/pix at 1000 cm⁻¹). This result suggests that the target-free wavelength-calibration method using solar Fraunhofer lines can be applied to other spectrometers simply by observing sunlit planetary surfaces.

The lunar south polar region, encompassing part of the South Pole-Aitken (SPA) basin, stands out as one of the most intriguing areas for future lunar exploration endeavors. Using the Moon Mineralogy Mapper (M³) data, we conducted a comprehensive investigation into the characteristics and distribution of minerals within the lunar south polar region, spanning from 80°S to the south pole. The cartographic outputs from this study, capable of delineating the composition and abundance of various minerals, have enabled the partitioning of the lunar south polar region into two distinct zones. The region situated within the inner ring of the SPA basin is characterized by an elevated abundance of low-Ca pyroxene, whereas the Feldspathic Highlands (FH) in the lunar south polar region and the outer ring of the SPA basin predominantly comprise feldspathic materials, albeit with localized pyroxene-rich areas. The dominant mafic component across the lunar south polar region is low-Ca pyroxene, with no evidence of olivine-rich materials being detected. The mineralogy of some candidate landing sites was illustrated and the hematite-bearing materials were observed at the rim of Shackleton and de Gerlache. Furthermore, we also identified an abundance plagioclase on the western rim of Shackleton. These findings underscore the significance of the lunar south polar region, not only as a promising locale for in situ resource utilization (ISRU) in forthcoming lunar missions but also as a key site for advancing our understanding of the Moon's geological evolution.