Icarus最新文献

The Rosetta spacecraft accompanied the comet 67P/C-G for nearly 2 years, collecting valuable data on the neutral and ion composition of the coma. The Rosetta Plasma Consortium (RPC) provided continuous measurements of the in situ plasma density while ROSINA-COPS monitored the neutral composition. In this work, we aim to estimate the composition of the cometary ionosphere at different heliocentric distances of the comet. Läuter et al. (2020) derived the temporal evolution of the volatile sublimation rates for 50 separated time intervals on the orbit of 67P/C-G using the COPS and DFMS data. We use these sublimation rates as inputs in a multifluid chemical-hydrodynamical model for 36 of the time intervals for heliocentric distances $<3$ au. We compare the total ion densities obtained from our models with the local plasma density measured by the RPC instruments. We find that at the location of the spacecraft, our modeled ion densities match with the in situ measured plasma density within factors of $1-3$ for many of the time intervals. We obtain the cometocentric distance variation of the ions H₂O⁺ and H₃O⁺ and the ion groups created respectively by the ionization and protonation of neutral species. We see that H₃O⁺ is dominant at the spacecraft location for nearly all the time intervals while ions created due to protonation are dominant at low cometocentric distances for the intervals near perihelion. We also discuss our ion densities in the context of their detection by DFMS.

Sticking of the dust grains is a critical step in planet formation. To investigate the solar wind effect on the dust mechanical properties, we conducted hydrogen implantation experiments (using beam energies of 10 keV, 20 keV and 50 keV) on olivine single crystals and determined the elastic modulus and the hardness as a function of depth by nano-indentation tests. The near surface regions of the samples (to ∼600 nm) show a substantial decrease in both hardness (up to ∼85%) and modulus (up to ∼74%), indicating a large degree of mechanical weakening. The depth extent of the weakened region increases with implantation energy while the degree of weakening decreases with implantation energy. TEM (transmission electron microscopy) observations of the samples show that the depth where damaged region occurs increases with the implantation energy used. The results are interpreted based on the physics of ion-solid interaction during implantation. According to our results, we expect that olivine-like dust exposed to solar wind would display a similar mechanical weakening in the surface (∼ 74% reduction in elastic modulus, ∼ 85% reduction in hardness). Mechanical weakening by solar wind implantation would enhance the sticking of the dust in the disk if dust have been effectively exposed to the solar wind. The present results are also applied to interpret observations of some planetary materials.

Venus’ retrograde rotation is the slowest of all planetary objects in the solar system. It is commonly admitted that such a rotation state results from the balance between the torques created by solid and atmospheric tides (Dobrovolskis and Ingersol, 1980; Correia and Laskar, 2001; Correia and Laskar, 2003a; Revol et al. 2023). The internal viscous friction associated with gravitational tides drives the planet into synchronization (i.e. deceleration to a tidally locked rotation) while the bulge due to atmospheric thermal tides tends to accelerate the planet out of this synchronization (Correia and Laskar, 2001; Leconte et al., 2015). The purpose of this work is first to provide an estimate of the viscosity of Venus’ mantle explaining the current balance with atmospheric forcing. A second goal is to quantify the impact of the internal structure and its past evolution on the rotation history of Venus.

Using atmospheric pressure simulations, we first provide an estimate of the atmospheric thermal torque value contrasting with previous estimates (Leconte et al., 2015). Computing the viscoelastic response of the interior to gravitational tides and to atmospheric loading (Dumoulin et al., 2017; Kervazo et al., 2021), we show that the current viscosity of Venus’ lower mantle must range between 2 × 10²⁰ Pa s and 6 × 10²¹ Pa s to explain a rotation in equilibrium. We then investigate the possible past evolution of Venus’ rotation by considering simple viscosity and thermal evolution paths. We show that in absence of additional dissipation processes, viscous friction cannot slow down Venus’ rotation to its current state from an initial rotation period shorter than 1 day.

In this study high-resolution stereo images and Digital Terrain Models (DTMs) from MErcury Surface, Space ENvironment, Geochemistry and Ranging (MESSENGER) mission were utilized to detect impact structures in regions not covered by Mercury’s Laser Altimeter (MLA), while gravitational data was utilized as a supported data set. We have established an inventory of 314 impact structures $\ge$150 km, classified on their morphological and gravitational characteristics. 24 basins $\ge$300 km have been newly discovered. Additionally, we have identified significant surface modifications in impact structures of smooth material infill, which can be either impact-induced or volcanic in origin. The Bouguer anomaly and crustal thinning in the center are displaying an interplay of predominant change of crustal structure in impact basins. Further, this study reveals a common impact history of Mercury and the Moon. Nevertheless, cumulative density distributions suggest the possibility of either a divergence in impactor populations responsible for forming large basins on both celestial bodies or a significant shift in impactor rates. This work holds important implications not only for understanding impact structure formation and evolution processes but also for interpreting the crustal structure. It presents an updated and expanded catalog of impact structures on Mercury, encompassing buried basins, and identifies new areas of interest, potentially serving as target sites for the forthcoming BepiColombo mission.

The aeolian transport of sand generates fine material through abrasion. On Mars this process occurs at lower temperatures than on Earth, however, there is minimal data on the effects of temperature on aeolian abrasion rates. Here, results are reported of laboratory experiments where a suite of single-phase, Mars relevant minerals (feldspar, olivine, pyroxene, quartz and opal) were exposed to conditions simulating aeolian abrasion at temperatures common to the Martian surface (193 to 293 K). Our results suggest that mineral specific differences in solid phase parameters result in non-similar changes in abrasion rates with temperature. We propose this will ultimately exert a control on the composition and reactivity of the Martian surface.

NASA's InSight lander monitored the Martian atmosphere while conducting its primarily geophysical investigation. Atmospheric imaging was used to study dust and ice at the site for over two Mars years in 2018–2022. An optical depth record, including dust and ice, was derived from systematic sky imaging in the mornings (for the first part of the mission) and evenings. Optical depths ranged from 0.5 to 1.9 but were typically under 1. Dust storms were seen at expected times in late northern autumn and early winter, including one shortly after landing, along with one late summer storm in January 2022. The optical depth record closely matched that of Curiosity, 600 km to the south, except for the expected additional water ice content during the aphelion cloud belt (ACB, spring to early summer). In addition to ice hazes, the ACB included discrete clouds, whose motion was tracked to show northeasterly to southeasterly daytime winds. While InSight recorded many meteorological vortices, no dust devils were seen, requiring that dust-devil occurrence was <10⁻³ times as common as during Spirit rover dust devil seasons.

The discovery of perchlorate in martian regolith, ubiquitously distributed at levels far exceeding those noted on Earth, raises challenges for in situ resource utilization and life-supporting systems. However, this challenge can be overcome by organisms with extreme tolerance to various stressors, characterization of the mechanisms supporting such features, and their subsequent employment in biological systems using genetic engineering and synthetic biology. Using such organisms could be an excellent complement to the physical and chemical technologies of perchlorate removal. Here, we review the research devoted to perchlorates on Mars, their types, spatial variability, age, and production mechanisms. We also characterize the perchlorate toxicity and the organisms (photosynthetic and chemoautotrophic bacteria as well as heterotrophic microorganisms and microinvertebrates) evidenced to withstand exposure to high perchlorate concentrations. The mechanisms behind this tolerance are also discussed in the context of future research prospects and their use in Mars exploration.

Many upcoming lunar missions and payloads are targeting the south pole of the Moon, due to the volatiles potentially harboured in this region including ESA's PROSPECT instrument. PROSPECT is designed to sample the lunar regolith within the first meter of the surface and to analyse any volatiles found. Remote sensing methods and a range of datasets including thermal models, illumination models, LRO NAC images, LOLA DEMs and LRO NAC DEMs generated with shape-from-shading, were used to identify suitable areas for PROSPECT science within the south polar region (84–90°S). Sites identified were down selected using a science matrix and scoring sites of interest based on if and how well the point of interest met the science requirements of PROSPECT. The highest scoring sites are presented and proposed to be ideal candidate landing sites for missions targeting the lunar south polar region, especially for missions that are interested in sampling volatiles, micro cold traps and Permanently Shaded Regions (PSRs). Understanding and sampling these colder areas within the south polar region will advance the understanding of volatiles within the lunar surface and volatile transfer.

The diurnal water cycle was studied at a Jezero crater base site using M2020 observations and adsorptive column modeling in a cool midwinter period just before a dust peak and at the peak. During low-dust sols 566–571 the observed air relative humidity (RH) at 1.45 m height was high, 40–90% near dawn. For the typical nocturnal wind speed of 2 m/s at 1.45 m and column water of 9.7 μm, the model's diurnal air temperatures and RH were within observations. For weaker winds model-RH increased as in some of the observed sols. In a nearly calm experiment fog formed from 1.45 m upward. Ground frost appeared independently of wind, but only if adsorption was disabled. The dust peak at around sol 577 was also well simulated with the same wind and absolute humidity as before the event, but relative humidities dropped dramatically due to the dust-enhanced higher nocturnal temperatures.