Planetary Surface Research Articles

Martian Atmospheric Spectral End‐Members Retrieval From ExoMars Thermal Infrared (TIRVIM) Data

AbstractKey knowledge about planetary composition can be recovered from the study of thermal infrared spectral range datasets. This range has a huge diagnostic potential because it contains diagnostic absorptions from a planetary surface and atmosphere. The main goal of this study is to process and interpret the dataset from the Thermal Infrared channel (TIRVIM) which is part of the Atmospheric Chemistry Suite of the ExoMars2016 Trace Gas Orbiter mission to find and characterize dust and water ice clouds in the atmosphere. The method employed here is based on the application of principal component analysis and target transformation techniques to extract the independent variable components present in the analyzed dataset. Spectral shapes of both atmospheric dust and water ice aerosols have been recovered from the analysis of TIRVIM data. The comparison between our results with those previously obtained on Thermal Emission Spectrometer (TES) data and with previous analysis on TIRVIM data, validates the methodology here applied, showing that it allows to correctly recover the atmospheric spectral endmembers present in the TIRVIM data. Moreover, comparison with atmospheric retrievals on PFS, TES and IRIS data, allowed us to assess the temporal stability and homogeneity of dust and water ice components in the Martian atmosphere over a time period of almost 50 years.

An alternative to Hapke’s macroscopic roughness correction

In this paper, we present an alternative to Hapke’s correction for the photometric effect of macroscopic roughness of planetary surfaces (Hapke, 1984). Our model includes the effects of both single-facet scattering and multi-facet scattering. The single-facet scattering model is derived directly from the definition of bidirectional reflectance of a rough surface. We model projected shadowing by adopting an approximation published elsewhere in the literature. Monte Carlo simulations of single-facet scattering demonstrate very good agreement with the single-facet scattering component of our model. Using 3D printed molds with known roughness statistics, we prepared rough mineral surfaces consisting of quartz and olivine in the laboratory. We recorded extensive measurements of the rough surface bidirectional reflectance over a wide range of illumination and view geometries at 1751 wavelength bands ranging from 500–2250 nm. By fitting the residual between the measured bidirectional reflectance and our single-facet scattering model, we developed an empirical approximation for multi-facet scattering. Our results show that the multi-facet scattering is proportional to the surface’s diffusive reflectance, RMS slope, and the cosine of the illumination angle. Furthermore, the multi-facet scattering is approximately Lambertian for phase angles less than 90° but becomes forward scattering at higher phase angles. Our empirical multi-facet scattering model incorporates all of these features. As a surface becomes more macroscopically rough, our data show that the overall reflectance distribution becomes progressively more backscattering in a way that is distinct from the shadow hiding opposition effect. We refer to this effect as the macroscopic roughness backscattering bias (MRBB), which affects the entire hemisphere rather than being localized to small phase angles. Our proposed model is more accurate than Hapke’s for phase angles less than 90°, and the accuracy of the two models is comparable at higher phase angles. However, researchers should be aware of an issue regarding the roughness parameter defined in Hapke’s model, namely the fact that “ϑ¯” is not actually equal to the mean slope angle of the surface for the probability density function used in the model. This is an issue which apparently has gone unnoticed in the literature, and has potentially caused the model to be applied incorrectly in past studies.

Influence of Planetary Surface Temperature on the Tectonic Transition from Heat Pipes (Simulation results and data extraction and plotting scripts)

Influence of Planetary Surface Temperature on the Tectonic Transition from Heat Pipes (Simulation results and data extraction and plotting scripts)

On the variation of apparent weight with altitude above a planet with an atmosphere

We study the variation of the apparent weight of an object with height above the surface of a planet with a (buoyant) atmosphere. Interestingly, this variation depends on two competing factors—the reduced gravitational acceleration (which acts to reduce the weight with increasing height) and the reduced buoyancy force in the progressively less dense atmosphere (which acts to increase the apparent weight of an object relative to its value at the planetary surface). The relative sizes of these two competing effects are evaluated for various bodies in the Solar System. For most planets, and the one pertinent moon (Titan), the effects are quite comparable in magnitude. However, the relatively tenuous atmosphere of Mars renders the reduced buoyancy effect negligible; the apparent weight of an object thus (as generally assumed) does decrease with height. At the other extreme, the very dense atmosphere of Venus makes the reduced buoyancy effect an order of magnitude more important than the effect of reduced gravitational acceleration, so that the apparent weight of an object increases with height in the Venusian atmosphere. In addition to deriving these intrinsic results (which are admittedly somewhat esoteric in nature), studying this problem presents students at the high-school or introductory undergraduate levels with an opportunity not only to develop a deeper appreciation of the underlying physics, but also to more fully appreciate the considerable power of parametric dimensional analyses in quickly and straightforwardly obtaining (here within a factor of two) a reasonably accurate solution to a problem. The degree to which that approximate solution is sufficiently interesting (and for this particular problem it turns out that the ‘sufficiently interesting’ threshold is indeed met) then informs whether or not a more rigorous mathematical approach is justified.

Present Day Endogenic and Exogenic Activity on Mercury

AbstractExogenic and endogenic activities dictate how planetary surfaces evolve. However, the present‐day influence of each of these activities is not well constrained. MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) temporal imaging recorded surface changes associated with these activities between 2011 and 2015. Here we present the results of a temporal investigation that identified 20 reflectance changes. One change exhibited bright rays extending from the site, consistent with the aftermath of an impact event. If all changes result from impact events, the present flux rate is 1,000 times higher than models predict. Consequently, we also report changes on slopes in areas with concentrations of tectonic landforms and identify a subset of changes that are on or adjacent to hollows, consistent with present‐day endogenic activities. Therefore, we conclude that these observations captured endogenic and exogenic modifications to the surface.

Effect of LIBS-Induced Alteration on Subsequent Raman Analysis of Iron Sulfides.

Mineral alteration is a possible side effect of spectroscopic techniques involving laser ablation, such as laser-induced breakdown spectroscopy (LIBS), and is related to the interaction of the generated plasma and ablated material with samples, dust, or ambient atmosphere. Therefore, it is essential to understand these interactions for analytical techniques involving laser ablation, especially for space research. In this combined LIBS–Raman analytical study, pyrite (FeS2) and pyrrhotite (Fe1–xS) samples have been consecutively measured with LIBS and Raman spectroscopy, under three different atmospheric conditions: ∼10–4 mbar (atmosphereless body), ∼7 mbar, and Martian atmospheric composition (Martian surface conditions), and 1 bar and Martian atmospheric composition. Furthermore, a dust layer was simulated using ZnO powder in a separate test and applied to pyrite under Martian atmospheric conditions. In all cases, Raman spectra were obscured after the use of LIBS in the area of and around the formed crater. Additional Raman transitions were detected, associated with sulfur (pyrite, 7.0 mbar and 1.0 bar), polysulfides (all conditions), and magnetite (both minerals, 1.0 bar). Magnetite and polysulfides formed a thin film of up to 350–420 and 70–400 nm in the outer part of the LIBS crater, respectively. The ZnO-dust test led to the removal of the dust layer, with a similar alteration to the nondust pyrite test at 7.0 mbar. The tests indicate that recombination with the CO2-rich atmosphere is significant at least for pressures from 1.0 bar and that plasma–dust interaction is insignificant. The formation of sulfur and polysulfides indicates fractionation and possible loss of volatile elements caused by the heat of the LIBS laser. This should be taken into account when interpreting combined LIBS–Raman analyses of minerals containing volatile elements on planetary surfaces.

Reflectance of silicate glasses in the mid-infrared region (MIR): Implications for planetary research

Volcanic phenomaena shaped the surface of all terrestrial planets in the solar system, and silicate glasses represent a major component in pyroclastic deposits and lavas. Spectral features of silicate glasses therefore influence spectral characteristics of large portions of planetary surfaces.In this study, experimental petrology techniques have been used to produce 19 silicate glass samples having natural chemical composition corresponding to four of the most common magmatic series on planet Earth. Reflectance of such products was investigated in the mid-infrared region (MIR) to observe the evolution of their spectral characteristics with changing degree of evolution (expressed as silica content) and alkaline content. We have observed how chemical features have a clear influence in shifting the spectral features (to lower wavelengths with increasing silica, such as for previously studied volcanic rocks) and on the spectral shape, which is substantially different between mafic and highly silicic products. This allowed us to propose a model to retrieve chemical information (SiO2 and SiO2 + Al2O3 + TiO2 content) from the wavelength at which spectral features (CF and RBpeak) occur. Moreover, by comparing our results with previous MIR studies we have observed that our model can be applied, to a certain extent, to interpret chemical fingerpint volcanic rocks in general. Here, it is also shown how granulometry influences spectral shape, but does not affect spectral shift.This study will be useful to interpret planetary information and assess how amorphous silicate phases influence spectral characteristics of volcanic areas on planetary surfaces.

A Minimally Cemented Shallow Crust Beneath InSight

AbstractIce and other mineral cements in Mars' shallow subsurface affect the mechanical properties of the shallow crust, the geologic processes that shape the planet's surface, and the search for past or extant Martian life. Cements increase seismic velocities. We use rock physics models to infer cement properties from seismic velocities. Model results confirm that the upper 300 m of Mars beneath InSight is most likely composed of sediments and fractured basalts. Grains within sediment layers are unlikely to be cemented by ice or other mineral cements. Hence, any existing cements are nodular or formed away from grain contacts. Fractures within the basalt layers could be filled with gas, 2% mineral cement and 98% gas, and no more than 20% ice. Thus, no ice‐ or liquid water‐saturated layers likely exist within the upper 300 m beneath InSight. Any past cement at grain contacts has likely been broken by impacts or marsquakes.

Martian surface dating model refinement based on Chang'E-5 updated lunar chronology function

Planetary surface ages are extremely important to geologic evolution studies. For extraterrestrial bodies, the crater size-frequency distribution dating method, including a crater production function and a chronology function, was established based on the radiometric ages of Apollo and Luna samples from the Moon. Recently, the radiometric age of a sample from Chang'e-5 mission added a data point where there was previously a gap in sample ages, and an updated lunar chronology function was proposed. This research aims to recalculate the Martian surface dating model from the newly updated lunar chronology function. The calculation takes account of the differences in impact rates, impact velocities, surface gravities, the threshold diameters of craters' transition from the strength to gravity regime and from simple to complex crater structures on the Moon and Mars. We use the Neukum production function, although other production functions could also be implemented with our method. A series of Martian isochrons is derived, and an approximated analytical form production function is provided for convenient applications in future studies. The Martian chronology function is finally obtained through fitting crater frequencies larger than 1.0 km in diameter with the corresponding ages of the isochrons. The resultant Martian PF and CF in this research are largely comparable with previous results. Based on the refined lunar chronology function, our model will enhance the reliability of the estimating Martian surface ages and we suggest it be used in future studies.

Analysis of Planetary Gear Transmission Characteristics Based on ANSYS

Planetary gear transmission is widely used in roadhead, crane and other transmission equipment, its reliability and stability are related to the service life and work efficiency of equipment, but the current research on planetary gear transmission device is not comprehensive, lack of accurate analysis of gear meshing process load. Therefore, in this paper, ANSYS software as a platform, through the construction of dynamics module, to solve the gear teeth surface, gear teeth root and gear teeth tip stress analysis and deformation and displacement, the finite element analysis. The research results provide necessary technical support for the design and production of planetary gear transmission.
 Aims: Through finite element analysis of planetary gear transmission, the dynamic parameters of planetary gear transmission are solved, and the reliability and stability of planetary gear transmission equipment are improved.
 Study Design: By constructing the dynamics module of planetary gear, the stress analysis, deformation and displacement of gear tooth surface, gear tooth root and gear tooth top are solved, and the finite element analysis is carried out.
 Place and Duration of Study: North China University of Water Resources and Electric Power, from March to July 2022.
 Methodology: The finite element analysis was carried out on the model of planetary gear transmission mechanism, and the model was established and simplified by using SolidWorks software. The modal analysis and dynamic analysis were carried out by using ANSYS software, and the meshes were divided and constraints were added. Finally, the parameters such as stress, strain and displacement of the meshing position were solved.
 Results: The result of model meshes is 357575 units and 204871 nodes. The algorithm has 219 iterations and 15 convergence points. The experimental results show that there is a meshing position with the worst contact fatigue strength in the contact area between the outer ring gear and the planetary gear tooth surface. At this position, the contact stress value of the tooth surface is 22626Pa.
 Conclusion: In this paper, the planetary gear device is modeled by SolidWorks software, and the finite element analysis is carried out by ANSYS software to obtain the stress and strain parameters in the transmission process of the device, as well as the worst meshing point of the gear, the most vulnerable point of fatigue and other dangerous points. It lays a certain technical foundation for the optimization and improvement of gear and the design and production of planetary gear transmission device.

Infrasound From Large Earthquakes Recorded on a Network of Balloons in the Stratosphere

AbstractThe ground movements induced by seismic waves create acoustic waves propagating upward in the atmosphere, thus providing a practical solution to perform remote sensing of planetary interiors. However, a terrestrial demonstration of a seismic network based on balloon‐carried pressure sensors has not been provided. Here we present the first detection of seismic infrasound from a large magnitude quake on a balloon network. We demonstrate that quake's properties and planet's internal structure can be probed from balloon‐borne pressure records alone because these are generated by the ground movements at the planet surface below the balloon. Various seismic waves are identified, thus allowing us to infer the quake magnitude and location, as well as planetary internal structure. The mechanical resonances of balloon system are also observed. This study demonstrates the interest of planetary geophysical mission concepts based on seismic remote sensing with balloon platforms, and their interest to complement terrestrial seismic networks.

Martian Glaciers May Have Carved Its Valleys

Networks of valleys provide puzzling hints of running water on the surface of the Red Planet. New research suggests that some tributaries could have formed from icy sheets thousands of meters thick.

Understanding dense granular flow from first principles

Preventing natural disasters like avalanches or landsides, optimising powder-based industrial processes or predicting the flow of sand on planetary surface, are exemplary applications that would benefit from a universal model for a better understanding of granular rheology. Due to the high densities and shear rates involved, the derivation of constitutive equations from first principles is notoriously difficult. Here, we will present such a theoretical approach, the Granular Integration Through Transients (GITT) formalism. Starting from the microscopic equations of motion, GITT yields quantitative predictions for the flow curves of granular fluids at high density and shear rate. GITT predicts Newtonian, shear thinning, and shear thickening regimes depending on density and shear rate. We will present experiments in a fluidized bed rheometer that confirm the rheological regimes and can be evaluated quantitatively in terms of GITT. We will discuss a phenomenological version of GITT that makes the qualitative behaviour understandable in terms of dimensionless numbers. With this we can derive the mu(I)-rheology that has been proposed as an empirical law for granular flow and show that it is a special case of GITT for specific flow conditions.

Earth and Planetary Surface Processes Perspectives on Integrated, Coordinated, Open, Networked (ICON) Science

AbstractThis article provides a commentary about the state of integrated, coordinated, open, and networked (ICON) principles in Earth and Planetary Surface Processes and discussion on the opportunities and challenges of adopting them. This commentary focuses on the challenges with current inclusive, equitable, and accessible science and highlights how research undertaken in the earth and planetary surface processes community currently benefit from and would be able to grow as a discipline with more directed implementation of ICON principles.

Analytic Approach to the Late Stages of Giant Planet Formation

This paper constructs an analytic description for the late stages of giant planet formation. During this phase of evolution, the planet gains the majority of its final mass through gas accretion at a rapid rate. This work determines the density and velocity fields for material falling onto the central planet and its circumplanetary disk, and finds the corresponding column density of this infalling envelope. We derive a steady-state solution for the surface density of the disk as a function of its viscosity (including the limiting case where no disk accretion occurs). Planetary magnetic fields truncate the inner edge of the disk and determine the boundary conditions for mass accretion onto the planet from both direct infall and from the disk. The properties of the forming planet and its circumplanetary disk are determined, including the luminosity contributions from infall onto the planet and disk surfaces, and from disk viscosity. The radiative signature of the planet formation process is explored using a quasi-spherical treatment of the emergent spectral energy distributions. The analytic solutions developed herein show how the protoplanet properties (envelope density distribution, velocity field, column density, disk surface density, luminosity, and radiative signatures) vary with input parameters (instantaneous mass, orbital location, accretion rate, and planetary magnetic field strength).

Packed media radiative-transfer modeling with Gaussian particles: Application to spectra of icy regolith of Saturnian satellites

The radiative transfer theory with packed media correction (RTT-PM) is a balanced, physically rigorous, and practical light scattering model that is suitable for modeling reflectance and similar spectra of densely packed particulate media. The static structure factor correction to the classical radiative transfer solution and actualization of fundamental particles of media with spheres or aggregates are key properties of this model that ensure both physical rigor and practical efficiency. We improved upon the assumptions in the RTT-PM method by incorporating irregularly shaped Gaussian particles into its scheme. This incorporation of Gaussian particles is a notable advancement for applications of the RTT-PM method to planetary surfaces that often are layers of irregularly shaped particles. With the Gaussian particle RTT-PM method, we modeled spectra of Saturnian moons Dione, Rhea, and Tethys observed with the Cassini Visual and Infrared Mapping Spectrometer (VIMS), assuming pure water ice composition. For Rhea and Tethys, the Gaussian particle RTT-PM technique modeled VIMS spectra better than models with spherical or aggregate particles, strengthening prior suggestion that particles on Rhea and Tethys are solid, non-spherical particles. Dione's spectra were best modeled not with Gaussian particles but rather with an aggregate of 128 monomers. This makes Dione's icy regolith different from that on Rhea and Tethys. Prior studies have indicated that the cause for the difference might arise from the presence of surface macrostructures or absorbing materials on Dione, but according to our modeling results, increased multiple scattering from small fluffy aggregate particles is an alternative explanation.

Catastrophic rupture of lunar rocks: Implications for lunar rock size–frequency distributions

Like many airless planetary surfaces, the surface of the Moon is scattered by populations of blocks and smaller boulders. These features decrease in abundance with increasing exposure time due to comminution by impact bombardment and produce regolith. Here we model the evolution of block size–frequency distributions by updating the model of Hörz et al. (1975) with new input functions: the size–frequency distributions of cm–scale meteoroids observed over the last few tens of years and a rock impact shattering function. The impact shattering function is calibrated using measurements of a lunar block size–frequency distribution of known age. We find that cumulative block size–frequency distributions change with time from a power–law for young populations (<~50 Myr) to an exponential distribution for older populations. The new destruction rates are within the uncertainty of the original model, although, for sizes >5 cm, they are two times faster than the original best estimate. The faster rates are broadly consistent with observations reported by other studies. Since the input functions are known for small rock sizes, the rock abundance can be determined theoretically at sizes below the current image spatial resolution (0.5 m). Surface exposure age of block fields can be estimated together with the initial block abundance from the measurement of block size–frequency distributions.

Sensitivity of Different Physics Schemes in the Simulation of Heat Wave Events over Bangladesh Using WRF-ARW Model

Heat waves (HWs) are an extreme temperature condition that has a direct impact on human lives. In recent years, a large number ofpeople have died all over the world due to hot weather. The purpose of this study is to predict HWs accurately to mitigate the casualtiescaused by them. Two HW events are selected for this study (Event-1: 0000 UTC of 18 May to 0000 UTC of 25 May 2015, Event-2:0000 UTC of 05 April to 2100 UTC of 08 April 2015). At first, sensitivity tests have been done using different combinations ofphysics schemes. Sensitivity of Planetary boundary layer (PBL) and surface layer (SL) schemes combinations (YSU-Revised MM5,YSU-MM5, MYJ-Eta, and ACM2-Revised MM5) and land surface models (RUC, Noah, Noah-MP, and CLM4) are investigated topredict Comfort Index (CI), which is identified by using Physiological Equivalent Temperature (PET). To simulate PET, the primarymeteorological variables 2-m air temperature (T2), 2-m relative humidity (rh2), mean radiant temperature (TMRT), wind speed at 10m (ws10), and cloud cover data have been used. These parameters were simulated by the WRF model using both single and nesteddomains. The experiments found that the combination of the YSU-MM5 scheme and the Noah land surface model predicted theWRF simulated variables very well. The study also found that the CI exists between the slight heat stress to extreme heat stress andthe maximum PET values were found to be 47.6 ºC and 48.5 ºC for Rajshahi and Khulna event respectively.&#x0D; Dhaka Univ. J. Sci. 70(1): 70-78, 2022 (January)

VUV photoabsorption of thermally processed carbon disulfide and ammonia ice mixtures – Implications for icy objects in the solar system

Many icy bodies in the solar system have been found to contain a rich mixture of simple molecules on their surfaces. Similarly, comets are now known to be a reservoir of molecules ranging from water to amides. The processing of planetary/cometary ices leads to the synthesis of more complex molecules some of which may be the harbingers of life. Carbon disulphide (CS2) and ammonia (NH3) are known to be present on many icy satellites and comets. Reactions involving CS2 and NH3 may lead to the formation of larger molecules that are stable under space conditions. In this paper we present temperature dependent VUV spectra of pure CS2 in the ice phase, and of CS2 and NH3 ices deposited as (i) layered, and (ii) mixed ices at 10 K and warmed to higher temperatures until their sublimation. Pure CS2 ice is found to have a broad absorption in the VUV region, which is unique for a small molecule in the ice phase. In layered and mixed ices, the molecules tend to affect the phase change and sublimation temperature of each other and also leave behind a form of CS2−NH3 complex after thermal annealing. This study of CS2-NH3 ice systems in layered and mixed configurations would support the detection of these species/complexes in mixed molecular ices analogous to that on planetary and cometary surfaces.

Kinetic isotope effects in H2O2 self-decomposition: Implications for triple oxygen isotope systematics of secondary minerals in the solar system

Hydrogen peroxide (H2O2) is a ubiquitous molecule in nature that shapes the redox state of planetary surfaces. Given that H2O2 is a major oxidant, isotope effects associated with H2O2 chemistry play a key role in determining triple oxygen isotopic compositions (δ17O and δ18O) of secondary aerosols and minerals, which are powerful proxies for understanding terrestrial/Martian atmospheric chemistry, and chemical evolution in the solar nebular. However, isotope effects in H2O2 self-decomposition processes, which actively occur in nature due to the thermal instability of H2O2, remains poorly understood. Here, we report a hitherto overlooked large and mass-dependent isotope fractionation in aqueous H2O2 self-decomposition processes quantified in a series of kinetic experiments. δ18O in remaining H2O2 is several tens of per mil (‰) with respective to initial H2O2. By synthesizing triple oxygen isotope measurements of natural H2O2, ozone, various oxyanions formed in the atmosphere (sulfate, nitrate, perchlorate, and carbonate), and oxygen-bearing secondary minerals in meteorites, we find that a decoupled Δ17O–δ18O pattern in natural H2O2 is attributed in part to the high degree of mass-dependent δ18O variation in H2O2 decomposition, and further argue that this unique signature may play a crucial role in triple oxygen isotope systematics in a board spectrum of secondary minerals in our solar system including aerosols, sediments, and meteorites. Our results shed fresh insights into recent debates on the role of H2O2 in the formation of these secondary minerals in the modern Earth, geological past, and other planets. The isotope effect experimentally quantified in this study are needed for future improvements of planetary atmosphere and solar nebular evolution models. We highlight the importance of further experimental and theoretical efforts to quantify isotope effects in H2O2 chemistry that are representative of natural systems.