Icarus最新文献

Diurnal and annual water cycles are studied during the first year of Perseverance rover in Jezero, using observations from the Mars Environmental Dynamics Analyzer (MEDA) and column modeling. Areal values for the ground thermal inertia (TI) and albedo are first found at one site by fitting model temperatures to the observed air temperatures. Areal soil porosity and the initial water vapor volume mixing ratios (vmr) are next found via model-vmr fits to the observation-based vmr. The meteorology and physics of the modeled air and subsurface diurnal moisture cycle at the site is then discussed in detail. The process of fit to observations is finally extended to fourteen sites along the Perseverance track, resulting in estimates for areal TI, albedo and porosity at these sites, and in MEDA-based initial estimates for the annual and diurnal moisture cycles at Jezero during MY36.

The European Space Agency (ESA) is developing a network of wide-field survey telescopes, named Flyeye, to improve the discovery of Near-Earth Objects (NEOs). The first telescope in the network will be located in the Northern Hemisphere on Mount Mufara (Italy), and a second Flyeye telescope, featuring increased detection capabilities, has just started the critical design phase.

The potential location for the second Flyeye telescope is investigated by performing simulations of NEOs on impacting trajectories. Approximately 3000 impacting asteroids of two absolute magnitudes (H = 25 and H = 28) were propagated and tested for detectability by major existing surveys (Catalina, Pan-STARRS, ATLAS), the upcoming Vera Rubin Observatory (LSST), and possible Flyeye locations. Chile, South Africa, and a second facility in the Northern Hemisphere were considered. For each observatory, their past or planned pointing strategies were taken into account in the simulation.

Before LSST deployment, a single Flyeye in the Southern Hemisphere performs similarly to a telescope in the Northern Hemisphere. When combined, having one telescope in the north and one in the south maximizes detections and number of unique objects detected. After LSST, southern and northern Flyeye telescopes remain complementary. Overall, simulations show that a second Flyeye in the south complements a Flyeye telescope in the north both before and after LSST. A Flyeye located at La Silla would take advantage of the excellent atmospheric conditions, while allowing a balance of assets across hemispheres.

Despite frequent observations of slope streaks and dust devil tracks on the same slopes in various regions on Mars, only a few instances in Arabia Terra have documented slope streaks directly triggered by dust devils. Here we present new observations of dust devil-induced slope streaks in Elysium Planitia and Amazonis Planitia. These observations represent a rare opportunity to study the erosional effects of both dust devils and slope streaks on the martian surface. Since dust devil tracks and the triggered streaks are formed basically simultaneously and are therefore subject to similar alteration processes, e.g., settling dust from the atmosphere, the relative albedo of these features can be determined using high-resolution orbital images. Our relative albedo analyses of twelve dust devil-induced slope streaks revealed that slope streaks appear substantially darker than the respective dust devil tracks. These observations might indicate a stronger erosion of fine-grained material by slope streaks compared to dust devils.

We utilize data from the MAVEN Radio Occultation Science Experiment (Withers et al., 2020) - with unprecedented coverage in solar zenith angle - to isolate the effects that local time and season induce on the photochemical ionosphere of Mars around solar minimum, leading to solar maximum. 185 out of the 1228 electron density profiles of the Martian undisturbed ionosphere collected by MAVEN ROSE between July 2016 and December 2022 show a distinct M1 layer below the M2 layer. We define undisturbed here as conditions when there are no solar events or dust storms to influence the ionosphere. This allowed us to study the behavior of both the M2 and M1 peak densities and altitudes as a function of solar zenith angle, and, for the first time, to be able to separate these trends by dusk and dawn local time, as well as by southern spring and summer versus southern fall and winter. We find that the M1 layer at small SZA can occur at altitudes lower than 100 km; that the peak altitudes and densities of both the M2 and M1 layers at dawn change more with season than they do at dusk; and that the M2 peak density decreases at a faster rate than the M1 with SZA.

The presence of organic matter in carbonaceous chondrites provides valuable information about the early composition of the Solar System. Although they are considered primitive, the majority of these chondrites have undergone secondary processes subsequent to their formation. These processes, such as aqueous alteration, have altered their composition. The effect of aqueous alteration on minerals is well known, but the effect on organic matter and/or on an organo-mineral system have been little studied. Here, we report experimental results devoted to investigate the chemical evolution of a hypothetical initial chondritic material subjected to hydrothermal alteration under reducing conditions at low-temperature. The mixtures consist of different anhydrous minerals (peridot, feldspar, troilite) together with hexamethylenetetramine (HMT) chosen as a model molecule inherited from the interstellar grains. After different times at 80 °C, the large molecular diversity formed is highly influenced by the presence and the nature of the minerals, as highlighted in particular by the evolution of the amide produced. The presence of minerals in the mixture appears to influence the reactivity of the system more through the formation of salts and chelates than through surface adsorption mechanisms. The most pronounced effect is observed in the presence of troilite, both in the degradation of HMT and in the abundance of amides formed. The study of the mutual influence of minerals and organic matter, and their intrinsic transformations in the media during the processes, could help to understand about the origin of organic molecules observed in carbonaceous chondrites.

Parga Chasmata is a 10,000 km long rift system on Venus with abundant coronae (enigmatic circular tectonomagmatic features). In order to further investigate the rift-corona relationship, detailed 1:500,000 geological mapping was focused on Onenhste Corona and the surrounding region (16°-24° S, 145°-131° W). More than 46,000 extensional lineaments were mapped and grouped into 50 sets, comprising 17 radiating, 28 circumferential and 5 linear sets (interpreted to overlie mafic dyke swarms). Radiating and circumferential swarms are linked with Onenhste Corona (OC), Momu Coronae (MC), Ulgen-ekhe Coronae (UEC), Rzhanitsa Corona (RzC, centred just outside the study area) and 5 Unnamed Coronae (UC1–5), as well as Malibran Patera (MP) and Fedchenko Patera (FP). Linear swarms are provisionally linked with magmatic centres outside the study area. Crosscutting relationships between the graben sets (dyke swarms) were used to identify the relative ages of magmatic centres. We applied an additional approach to recognize coeval centres, the swinging or deflection of radiating and circumferential dyke swarms to reveal the stress interaction between different coeval centres. The relative ages (oldest to youngest) of the magmatic centres are UC2 > RzC > MC ≥ OC = UC1 = UEC ≥ MP > UC5, and FP > UC3. These new detailed data provide significant information on coronae timing, evolution and relation to rift zones that will serve as a basis for future quantitative studies of lithospheric and mantle evolution and the combined cause and effect of rifting and mantle diapiric upwelling.

Several centres, RzC, UC2, MC, UC3 and FP, ordered from NW to SE, are aligned along a trend parallel to Parga Chasmata but offset about 900 km to the south from the main zone of rifting. It is inferred that this alignment is related to a zone of weakness associated with the rift extension. Along this trend the centres do not show an age progression.

Coronae MC, OC, UC1 and UEC are aligned along the NNE trending P13 Linea, orthogonal to the main Parga Chasmata rift. The main centre, Onenhste, is coeval with UC1, which in turn is coeval with UEC. Additional age relationships indicate that the late stage of OC was active at the same time as MP, MC and the UC2–9 centre of UC2. Linea P13 is older than Chondi Chasma. This study, and continuing, detailed geological mapping and analysis are increasing our understanding of the relationships between the formation of the main WNW trending Parga Chasmata rift zone, the orthogonal trends of rifting and the numerous magmatic centres (mainly coronae) distributed along both trends.

Mesospheric CO₂ clouds are one of two types of carbon dioxide clouds known on Mars. We present observations of mesospheric CO₂ clouds made by Atmospheric Chemistry Suite (ACS) onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter (TGO). We analyzed 1663 solar occultation sessions of Thermal InfraRed (TIRVIM) and Middle InfraRed (MIR) channels of ACS covering more than two Martian years that contain spectra of 2.7 μm carbon dioxide ice absorption band. That allowed us to unambiguously discriminate carbon dioxide ice aerosols from mineral dust and water ice aerosols, not relying on the information of atmospheric thermal conditions. CO₂ clouds were detected in eleven solar occultation observations at altitudes from 39 km to 90 km. In five cases, there were two or three layers of CO₂ clouds that were vertically separated by 5–15 km gaps. Effective radius of CO₂ aerosol particles is in the range of 0.1–2.2 μm. Spectra produced by the smallest particles indicate a need for a better resolved CO₂ ice refractive index. Nadir optical depth of CO₂ clouds is in the range 5 × 10⁻⁴–4 × 10⁻² at both 2.7 μm and 0.8 μm. Asymmetrical diurnal distribution of detections observed by ACS is potentially due to local time variations of temperature induced by thermal tides. Two out of five cases of carbon dioxide cloud detections made by the TIRVIM instrument reveal the simultaneous presence of CO₂ ice and H₂O ice aerosols. Temperature profiles measured by the Near InfraRed (NIR) channel of ACS are used to calculate CO₂ saturation ratio S at locations of carbon dioxide clouds. Supersaturation S > 1 is detected in only 6 out of 19 cases of CO₂ cloud layers; extremely low values of S < 0.1 are found in 9 out of 19 cases.

C/2017 K2 (Pan-STARRS) is an Oort cloud comet discovered in May 2017. Ground observations have revealed that this long-period comet was active at a heliocentric distance beyond 20 au. Several studies observed this object when it was far from the Sun and proposed that, at such a distance, its activity is primarily driven by the sublimation of super-volatile ices such as $\mathrm{CO}$ and ${\mathrm{CO}}_2$.

The aim of this paper is to analyze the comet’s dust behavior when it was much closer to the Sun. A series of images were taken on different observation routines between July and August 2022 with the 0.6 m Helen Sawyer Hogg (HSH) telescope at the Complejo Astronómico El Leoncito (CASLEO), using broadband V and R filters. The objective was to conduct a morphological, photometric, and numerical analysis of this comet.

Digital filters were applied to enhance contrast in the cometary images, revealing an active region embedded within an isotropic coma. Analysis of the magnitudes and dust production rate from the $A(0°)f\rho$ parameter suggests a steady-state dust behavior, consistent with findings from other authors.

Moreover, thanks to the images covering a significant time span, it was possible to determine the comet’s rotation period using a periodogram analysis with the Phase Dispersion Minimization method (PDM) and to calculate the coordinates of the rotation axis, yielding a rotation period of 14.24 h with a pole situated at the ecliptic longitude and latitude of $(244°,-20°)$.

Finally, to gain deeper insights into C/2017 K2’s dust behavior, observations were fitted to a newly developed theoretical model for studying dust comas. The analysis suggests that the comet’s dust coma was principally formed by large dust particles emitted at a velocity of $180{\mathrm{ms}}^{-1}$.

The relationship between chasmata (rift zones) and spatially associated volcanism (mons and coronae) on Venus has been extensively discussed but remains enigmatic. One region where these features are prominently displayed is along the 10,000 km long, WNW trending, Parga Chasmata, which connects Atla Regio with Themis Regio. The Mbokomu Mons area (located about 2200 km SE of Atla Regio) was selected for detailed study to provide insight into these relationships. More than 39,000 extensional lineaments (grabens, fissures and fractures) were mapped at 1:500,000 scale using full resolution Magellan Synthetic Aperture Radar (SAR) images and grouped into radiating, circumferential and linear systems. They are (except where noted) interpreted to represent the surface expression of underlying mafic dyke swarms, on the basis of associated volcanic features and terrestrial analogues. Radiating and/or circumferential swarms are associated with Mbokomu Mons and the four coronae in the surrounding area, Among Corona (AC), Repa Corona (RC) and two unnamed coronae (UC1 and UC2). Mbokomu Mons is unique among the tectono-magmatic features in this region of Parga Chasmata, in having both corona and mons characteristics. The initial Corona Phase consists of radiating and circumferential systems mainly preserved in an unflooded annular uplift, while the Mons Phase includes a second radiating swarm associated with a central edifice, and smaller circumferential fracture pattern near the summit that could overlie a magma reservoir. The plume or diapir that is interpreted to have been responsible for the initial Corona Phase is estimated to have had a radius of ∼150 km. Cross-cutting relationships indicate that Mbokomu Mons is younger than nearby Among, Oduduwa and Onenhtse coronae. All four centres are aligned along a WNW-trend parallel to the Parga Chasmata (rift system). Mbokomu Mons is located at, and its emplacement may be linked to, the intersection of this WNW-trending zone of weakness and the orthogonal Jokwa Linea rift system. Mbokumo Mons is also younger than the nearby parallel Penthesilia Fossa (PF) (part of the Great Dyke of Atla Regio).

The seasonal variation of the Martian South Polar Seasonal Cap (SPSC) is a significant factor to influence Mars atmospheric cycle, which has been continuously observed in previous missions. The SPSC degrades asymmetrically throughout the Martian seasons. However, developing a general description for this asymmetric recession is challenging, and this is crucial for identifying key stages (timesteps) which represents moments of special attribute throughout the recession. Here, we present the Martian Year 36 (MY36) results from the continuous observation of the Martian SPSC by the Moderate Resolution Imaging Camera (MoRIC) onboard the Tianwen-1 orbiter. A time-series of digital orthophoto maps (DOMs) characterizing the south cap were collected ranging from the solar longitude (L_s) 210° to 332°. A seasonal recession model of the cap was established by incorporating a 5th-order polynomial fitting of the time-series on cap latitude, from which the first derivative (recession rate), second derivative (acceleration), and third derivative (jerk) can be obtained. This methodology enables the extraction of critical timesteps that facilitate the categorization of the recession into distinct phases, each characterized by its recession rate and other factors. By the visual interpretation of remote sensing images obtained by Tianwen-1 and the result of timesteps showed that the pause time of the South Polar Residual Cap (SPRC) is about L_s = 324.5°-328° with an area of 7.9 × 10⁴ km². The discrepancies between our results and previous investigations indicate that the Martian climate presents inter-annual fluctuations. The MoRIC image data can be used to quantitatively capture the fine recession dynamic of the southern polar cap.The continuous operation of the Tianwen-1 orbiter will enable further data analysis for the dynamics of the Martian polar caps. This will provide observational constraints for Martian climate models and crucial information for the research of the Martian modern climate.