Icarus最新文献

Knowledge of collision-induced absorptions (CIA) by pure CO₂ for wide temperature ranges is necessary for atmospheric and climate studies of planets and exoplanets with CO₂-rich atmospheres. In this work, using spectra measured with a Fourier transform spectrometer for temperatures between 230 K and 295 K at pressures up to 40 bar, several CIA bands in the 1150–4500 cm⁻¹ spectral range have been determined, in some cases for the first time. The results are compared with values reported in the literature, showing good agreements. From data obtained in this work and those in the literature, we propose simple analytical models for the temperature dependent band shape and integrated band intensity (IBI) which enable the calculation of all investigated CIA transitions in a wide temperature range.

S1094b is the largest (155 m-size) and southernmost known ice-exposing fresh crater discovered so far on Mars, revealing a relatively pure and unstable subsurface ice deposit located at the northern Martian mid-latitudes. In this work, we analyze HiRISE images taken on 27 February 2022 and on 5 December 2022 to perform a multi-temporal analysis of its ice-rich ejecta, combining this analysis with geologic mapping, the boulder size frequency distribution (SFD) and thermal modeling. The objective is to provide a multidisciplinary characterization of both the impact and subsequent exposed ice sublimation processes. The boulder SFD of both February and December cases show a power-law best fit with indices −4.68 ± 0.15 and − 3.47 ± 0.10, respectively. In the same timeframe, the density of boulders per km² ≥ 1.5 m changes from 3908, to 596. This flattening is mainly due to the sublimation and consequent loss of the smaller-size icy boulders. This is confirmed by the ice volume computation performed on the area, which changed from ∼20,274 ± 3997 m³ to ∼7951 ± 1117 m³, i.e. a decrease of ∼60% in 274 Sols. The thermal models showed that the ice in this region is always unstable, leading to a total of 6504.71 sublimation hours from which we estimated a sublimation rate of ∼0.15 ± 0.04 mm/h (i.e. ∼3.60 ± 0.96 mm/Sol). The presence of this amount of accessible ice at such low latitudes could be a valuable resource for potential future human missions.

Exploring the concealed subsurface structures and materials beneath the lunar surface can reveal significant insights into geological history. This study offers a comprehensive analysis of the stratigraphic interpretation and subsurface material composition at the Chang'E-4 landing site, integrating both in-situ and orbital radar with multispectral datasets. We report the identification of a subsurface structure, which resembles a buried impact crater (∼420 m in diameter) under the Yutu-2 rover's path. This crater could degrade over a period of 0.42 to 0.53 Ga, with an initial diameter of 293 to 323 m and an initial depth of 45.9 to 51.4 m. Surface material above the buried crater, evaluated by the in-situ visible and near-infrared imaging spectrometer (VNIS) detector, shows a higher abundance of clinopyroxene compared to surrounding areas, where a near-equal mix of clinopyroxene and orthopyroxene is observed. Assessment of crater diameters in proximity to the Chang'E-4 landing site, along with the mineral compositions at their epicenters, reveals a decrease in the abundance of clinopyroxene and plagioclase with depth. Conversely, the quantities of orthopyroxene and olivine increase, implying that orthopyroxene-rich Finsen ejecta significantly influenced the Chang'E-4 landing site's geological composition. Two potential stratigraphic boundary depths are identified at 13.5 and 22 m, based on pronounced variations in mineral abundance, offering fresh insights into subsurface delineation beyond radar data. Considering the VNIS and vertical mineral composition, we propose the buried crater's formation resulted from Finsen crater's ejecta. Also, we identify eight potential historical impacts by comparing subsurface relief variations with mineral composition ratios between clinopyroxene and orthopyroxene. The integration of subsurface structure, along with surface and subsurface mineral composition, enables a more robust stratigraphic interpretation, facilitates shallow material source analysis, and allows for historical impact tracing.

The detrimental effects and challenges of Lunar dust for Lunar exploitation were first identified during the Apollo missions. During the extra vehicle activities (EVAs) undertaken by astronauts, the dust clogged mechanisms, disrupted sensors, and caused several health issues for the astronauts. Despite numerous studies, there is no definite understanding as to why different Apollo missions experienced varying levels of dust disruptions. The variations in dust behaviour could be attributed to the amount of radiation the Lunar soil is exposed to, as well as mineralogy and particle sizes. To enhance our understanding of Lunar dust behaviour this study investigated Space Recourse Technologies, formally known as Exolith, simulant at different mineral compositions, and their surface detachment characteristics were measured. Experiments measuring the individual minerals and their mixed simulant-like counterparts were conducted using electrostatic fields. Inclusive to this, non-dried and dried samples were compared by measuring adhesion to target plates when subject to electrostatic forces. The results found that Highlands simulant exhibited a higher buildup on a target plate than its Mare counterpart by an average of 33% under the same conditions, likely due to particle size differences. In addition to these findings, evidence of particle reactivity decay was observed under repeated tests with up to 60% less Mare simulant and 36% Highlands deposition being measured compared to the first set of experiments. A possible explanation may be particle reactivity. Microscope images identified that particles are transported in groups as opposed to individual grains. These results will help researchers in tailoring dust mitigation solutions based on different regions on the Lunar surface and influence mission planning from the perspective of dust mitigation and contamination.

At present, the main satellites of Uranus are not involved in any low order mean motion resonance (MMR). However, owing to tides raised in the planet, Ariel and Umbriel most likely crossed the 5/3 MMR in the past. Previous studies on this resonance passage relied on limited time-consuming $N-$body simulations or simplified models focusing solely on the effects of the eccentricity or the inclination. In this paper, we aim to provide a more comprehensive view on how the system evaded capture in the 5/3 MMR. For that purpose, we developed a secular resonant two-satellite model with low eccentricities and low inclinations, including tides using the weak friction model. By performing a large number of numerical simulations, we show that capture in the 5/3 MMR is certain if the initial eccentricities of Ariel, $e_1$, and Umbriel, $e_2$, are related through ${(e_1^2+e_2^2)}^{1/2}<0.007$. Moreover, we observe that the eccentricity of Ariel is the key variable to evade the 5/3 MMR with a high probability. We determine that for $e_1>0.015$ and $e_2<0.01$, the system avoids capture in at least 60% of the cases. We also show that, to replicate the currently observed system, the initial inclinations of Ariel and Umbriel must lay within $I_1\le 0.05°$ and $0.06°\le I_2\le 0.11°$, respectively. We checked these results using a complete $N-$body model with the five main satellites and did not observe any significant differences.

Near-Earth Asteroids (NEAs) are excellent laboratories for processes that affect the surfaces of airless bodies. Most NEAs were not expected to contain OH/H₂O on their surfaces because they are primarily S-complex objects and sourced from the inner Main Belt, which is interior of the frost line, and their surface temperatures are high enough to remove these volatiles. However, a 3-μm feature typically indicative of OH/H₂O was identified on other seemingly dry bodies in the inner Solar System, such as the Moon and Vesta, and more recently on the NEAs (433) Eros, (1036) Ganymed, and (3122) Florence. The most likely sources for OH/H₂O on these bodies include carbonaceous chondrite impacts or interactions with protons implanted by solar wind. We investigated the causes of band depth and shape variations on NEAs by comparing new observations of Eros and Ganymed to those previously published and conducting a rotationally-resolved spectral study on Florence. All spectra discussed were collected by SpeX on NASA's IRTF using the LXD_short (1.67–4.2 μm) mode to characterize the 3-μm region. Some observations also used the prism (0.7–2.52 μm) mode to characterize asteroid spectral type and investigate silicate composition dependencies. All three asteroids possess exogenously sourced OH/H₂O and have spectra that show potential spatially correlated variations in band depth or shape. Eros' band is slightly wider at the poles than at lower sub-observer latitudes, possibly due to its high obliquity, which ensures that each polar region is oriented toward the Sun over a significant part of its orbit. Ganymed's trends in hydration band depth with sub-solar longitude and band I center suggest a carbonaceous or cometary impactor that struck the surface around 0° relative longitude, excavating a relatively magnesium- and olivine-enriched layer. Florence's total hydrogen concentration remains stable across the surface even as the OH-to-H₂O ratio changes as the asteroid rotates. These three examples suggest that non-native OH/H₂O on other bodies will likely also be spatially dependent, regardless of delivery mechanism.

A set of 28 different meteorites was tested in 32 ablation experiments in the plasma wind tunnel PWK1 at the Institute of Space Systems. All meteorites were exposed to the same flow condition in consecutive experiments. This paper presents the detailed analysis of high-resolution images taken by DSLR cameras during 26 experiments on 22 different meteorites. It is seen that the ablation behavior of the meteorites differs in the way the material melts and flows downstream. While some meteorites appeared more viscous and most material remained connected to the main body, other samples suggest a much lower viscosity as the material was carried downstream and released droplets to the flow. Most droplets of molten material were seen for the two most carbon rich samples from meteorites Murchison and Dhofar 1575. The release of blue colored particles was observed for several meteorites, independent of the viscosity. In contrast to the molten droplets, the blue particles also traveled up to a few millimeters upstream. The abundance of these blue particles is linked to the iron content. Close to no particles or droplets were observed for achondritic samples.

The total energy of a fireball is commonly obtained from optical measurements with an assumed value for luminous efficiency. Acoustic energy measurements offer an independent means of energy estimation. Here we combine optical and acoustic methods to validate the luminous efficiency model of Borovičkaet al. (2020). Our goal is to compare these models with acoustic measurements of meteoroid energy deposition. Employing theoretical blast scaling laws following the approach of Mcfaddenet al. (2021), we determine explosive yields for both fireball fragmentation events and cylindrical shocks for four different bright fireballs. We model fireballs using the MetSim software (Vidaet al., 2023) and find that the Borovičkaet al. (2020) model produces agreement better than a factor of two for our three chondritic fireball case studies. The major exception is an iron meteorite-producing fireball where the luminous efficiency is an order of magnitude higher than model predictions calibrated with stony fireballs. We suggest that large disparities between optical and acoustic energies could be a signature of iron fireballs and hence useful as a discriminant of that population.

Aggregated particles and aerosols are common in natural or industrial environments. Analysing their scattering and absorption properties with precise methods may prove useful for gaining information about real particles, using remote sensing or in situ active optical instruments in natural environments. Many methods, with varying complexities, were developed in the past. For aggregates of spheres, the most recent version of the T-Matrix method by Mackowski and Mishchenko (2011) is able to treat the problem almost exactly and can yield all the details of the scattering properties. However, for computational reasons, the T-Matrix method cannot handle large particles. In order to deal with large particles, a mean-field version of the T-Matrix theory was developed by Botet et al. (1997) for aggregates of identical spheres and used in particular to analyse the case of Titan haze. This mean-field T-Matrix method is efficient to quickly calculate accurate approximations of many optical properties of aggregates of Mie spheres, but it is inherently limited by the mean field approximations. It uses crude approximation of the pair-correlation functions (Seignovert et al., 2017) and leads to inaccurate estimations in the geometrical optics limit (Tazaki and Tanaka, 2018). In the present work, we bring improvements that overcome these two limitations. This significantly increases the validity range of the method and its accuracy. We display comparisons with the results obtained with T-Matrix method in order to assess the performance of the new version of the mean field method (MFT-M${}^{+}$).

Titan’s surface and lower atmosphere support a hydrologic cycle that influences various aspects of the icy moon’s appearance and evolution. Here, we review the state of knowledge around this methane cycle, focusing on its relationship to the circulation of the troposphere and to the distribution of surface liquids. Titan’s meridional circulation consists mainly of Hadley cells, with an intertropical convergence zone—in which clouds and precipitation are promoted—that oscillates with latitude seasonally. There are separate regions at the poles wherein precipitation occurs in summertime. Overall, the character of precipitation depends on the amount of liquid available to evaporate on the surface, and a realistic liquid distribution (that is, with liquids limited to polar regions) leads to highly sporadic seasonal precipitation. This also produces a latitudinal profile of near-surface humidity wherein the poles are more humid than the lower latitudes. The lower latitude humidity reflects the horizontal transport by the Hadley circulation, but is cut off from the high near-surface humidity at the poles. Polar moist convection humidifies the mid-levels and from there the low latitudes, and equatorward, downgradient transport of moisture is accomplished by traveling storm systems in the high mid-latitudes. These waves in some cases interact with the convection to communicate the effects of latent heating nearly globally. Separately, surface and subsurface hydrology are important processes that lead to the observed distribution of liquids in polar basins, and furthermore indicate the influence of a subsurface methane table interacting with the climate system. Precipitation at lower latitudes largely runs off or infiltrates into the surface; runoff at higher latitudes feeds some of the low-lying polar basins; and subsurface methane flow regulates the distribution of near-surface methane such that the seas are surface exposures of, and other polar areas sustain evaporation from, a shallow methane table. Finally, we discuss the possible long-term evolution of surface liquids, including the influence of Croll-Milankovitch cycles and their effect on atmospheric moisture transport by eddies; whether or not Titan’s surface features indicate past cycling of polar liquids, slower secular trends, or something else entirely remains unresolved.