Search

Context. Identifying minerals on asteroid surfaces is difficult as space weathering modifies the minerals infrared spectra. This shouldbe better understood for proper interpretation. Aims. We simulated the space weathering effects on a meteorite and recorded the alterations of the crystalline structure, such as the change in peak positions and full width at half maximum values. Methods. We used proton irradiation to simulate the effects of solar wind on a sample of NWA 10580 CO3 chondrite meteorites. After irradiation in three gradually increased steps with 1 keV ion energy, we used infrared microscopic reflectance and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to identify and understand the consequences of irradiation. Results. We find negative peak shifts after the first and second irradiations at pyroxene and feldspar minerals, similarly to the literature, and this shift was attributed to Mg loss. However, after the third irradiation a positive change in values in wavenumber emerged for silicates, which could come from the distortion of SiO4 tetrahedra, resembling shock deformation. The full width at half maximum values of major bands show a positive (increasing) trend after irradiations in the case of feldspars, using IR reflection measurements. Comparing DRIFTS and reflection infrared data, the peak positions of major mineral bands were at similar wavenumbers, but differences can be observed in minor bands. Conclusions. We measured the spectral changes of meteorite minerals after high doses of proton irradiation for several minerals. We show the first of these measurements for feldspars; previous works only presented pyroxene, olivine, and phyllosilicates.

Before the seasonal polar ice cap starts to expand towards lower latitudes on Mars, small frost patches may condensate out during the cold night and they may remain on the surface even during the day in shady areas. If ice in these areas can persist before the arrival of the contiguous ice cap, they may remain after the recession of it too, until the irradiation increases and the ice is met with direct sunlight. In case these small patches form periodically at the same location, slow chemical changes might occur as well. To see the spatial and temporal occurrence of such ice patches, large number of optical images should be searched for and checked. The aim of this study is to survey the ice condensation period on the surface with an automatized method using a Convolutional Neural Network (CNN) applied to High-Resolution Imaging Science Experiment (HiRISE) imagery from the Mars Reconnaissance Orbiter mission. The CNN trained to recognise small ice patches is automatizing the search, making it feasible to analyse large datasets. Previously a manual image analysis was conducted on 110 images from the southern hemisphere, captured by the HiRISE camera. Out of these, 37 images were identified with smaller ice patches, which were used to train the CNN. This approach is applied now to find further images with potential water ice patches in the latitude band between -40{\deg} and -60{\deg}, but contrarily to the training dataset recorded between 140-200{\deg} solar longitude, the images were taken from the condensation period between Ls = 0{\deg} to 90{\deg}. The model was ran on 171 new HiRISE images randomly picked from the given period between -40{\deg} and -60{\deg} latitude band, creating 73155 small image chunks. The model classified 2 images that show small, probably recently condensed frost patches and 327 chunks were predicted to show ice with more than 60% probability.

The interior of Enceladus, a medium sized icy moon of Saturn hosts hydrothermal activity and exhibits tidal heating and related geyser-like activity. There are major disagreements in the existing literature on the porosity of the interior, due to the different theoretical assumptions on which porosity related calculations were based. We present an application of experimental equations - derived for Earth - for icy planetary objects and Enceladus in particular. We chose a set of boundary values for our initial parameters from measured porosity values of chondrite samples as references, and calculated the porosity related values of Enceladus using various approaches. We present a comprehensive investigation of the effects of using these different porosity calculation methods on icy moons. With our most realistic approach we also calculated the same values for Earth and Mars for comparison. Our result for Enceladus is a minimum porosity of about 5\% at the centre of the body. For the total pore volume we estimated $1.51*10^7 km^3$ for Enceladus, $2.11*10^8 km^3$ for Earth and $1.62*10^8 km^3$ for Mars. Using the same method, we estimated the total pore surface area. From this we derived that the pore surface under a given $1 km^2$ area of the surface on Enceladus is about $1.37*10^9 km^2$, while for Earth this value is only $5.07*10^7 km^2$., Comment: 8 pages, 9 figures

The search for ephemeral liquid water on Mars is an ongoing activity. After the recession of the seasonal polar ice cap on Mars, small water ice patches may be left behind in shady places due to the low thermal conductivity of the Martian surface and atmosphere. During late spring and early summer, these patches may be exposed to direct sunlight and warm up rapidly enough for the liquid phase to emerge. To see the spatial and temporal occurrence of such ice patches, optical images should be searched for and checked. Previously a manual image analysis was conducted on 110 images from the southern hemisphere, captured by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter space mission. Out of these, 37 images were identified with smaller ice patches, which were distinguishable by their brightness, colour and strong connection to local topographic shading. In this study, a convolutional neural network (CNN) is applied to find further images with potential water ice patches in the latitude band between -40{\deg} and -60{\deg}, where the seasonal retreat of the polar ice cap happens. Previously analysed HiRISE images were used to train the model, where each image was split into hundreds of pieces (chunks), expanding the training dataset to 6240 images. A test run conducted on 38 new HiRISE images indicates that the program can generally recognise small bright patches, however further training might be needed for more precise identification. This further training has been conducted now, incorporating the results of the previous test run. To retrain the model, 18646 chunks were analysed and 48 additional epochs were ran. In the end the model produced a 94% accuracy in recognising ice, 58% of these images showed small enough ice patches on them. The rest of the images was covered by too much ice or showed CO2 ice sublimation in some places.

On Mars it is possible that after the recession of the seasonal polar ice cap, small icy patches left behind in shady places due to the low thermal conductivity of the Martian surface and atmosphere, are met by direct sunlight during the summer. These patches might warm up substantially and we analyzed below how could a liquid phase emerge in these places, surveying HiRISE images. 730 images that fit the selection criteria of location and season were analyzed, and we identified 148 images with smaller ice patches on them. Their separation from other bright patches, like clouds or lighter shades of layers and rocks were possible by their bluish color and strong connection to local topographic shading. These areas range between 140{\deg} and 200{\deg} solar longitude in the latitude band between -40{\deg} and -60{\deg}. The diameter of the ice patches ranges between 1.5-300 meters, and they remain on the surface even after the seasonal polar cap has passed over the area for the duration range of 19-133 martian days. With the help of The Mars Climate Database (MCD) we simulated the surface temperature and predicted CO2 and H2O ice cover at 22 analyzed areas. Judging by the models, the average noon temperature does not reach the melting point of water, which is 273 K, therefore the occurrence of liquid water on the macroscopic scale is highly unlikely, however there is a possibility that an interfacial premelting of ice (a few nanometers thick waterlayer) might form between the layered and the water ice.

Here we present an improved algorithm to model the serpentinization process in planetesimals in the early Solar system. Although it is hypothesized that serpentinization-like reactions played an important role in the thermal evolution of planetesimals, few and restricted models are available in this topic. These processes may be important as the materials involved were abundant in these objects. Our model is based on the model by (Gobi & Kereszturi 2017), and contains improvements in the consideration of heat capacities and lithospheric pressure, and in the calculation of the amount of interfacial water. Comparison of our results with previous calculations shows that there are significant differences in the e.g. the serpentinization time -- the time necessary to consume most of the reactants at specific initial conditions -- or the amount of heat produced by this process. In a simple application we show that in icy bodies, under some realistic conditions, below the melting point of water ice, serpentinization reaction using interfacial water may be able to proceed and eventually push the local temperature above the melting point to start a 'runaway' serpentinization. According to our calculations in objects with radii R $\gtrsim$ 200 km serpentinization might have quickly reformed nearly the whole interior of these bodies in the early Solar system., Comment: Accepted for publication in the Planetary Science Journal

There may be a chance of small-scale ephemeral liquid water formation on present day Mars, even though the current climate does not support the existence of larger bodies of water. Through a process called deliquescence, hygroscopic salts can enter solution by absorbing water vapor directly from the atmosphere. Due to the absence of in-situ deliquescence experiments so far, the most reliable way to forecast deliquescence is through atmospherical modeling, however, the locations and times when salty liquid water could emerge are not yet well known. In this paper we present our results of likely brine formation on Mars, their proposed locations and seasons, as well as the possible limiting factors. For our calculations we used the data of Laboratoire de M\'et\'eorologie Dynamique Mars General Circulation Model version 5. The results show that from L$_s$ 35$^\circ$ - L$_s$ 160$^\circ$, between 9 PM and 11 PM there is a good chance for calcium perchlorate deliquescence above 30$^\circ$ N, while in this zone the ideal regions are concentrated mostly to Acidalia Planitia and Utopia Planitia between 1 AM and 3 AM. We found that in the Southern Hemisphere, between L$_s$ 195$^\circ$ and L$_s$ 320$^\circ$, there is a noticeable, but weaker band in the vicinity of 60$^\circ$ S, and both Argyre Planitia and Hellas Planitia show some chance for brine formation. According to our statistics the key limiting factor of deliquescence could be relative humidity in most cases. Our results suggest that during summer -- early fall seasons, there could be deliquescence in both hemispheres in specific areas from the late evening until the early morning hours. There are only few studies detailing the geological and temporal distribution of brine formation through deliquescence, thus this work could be used as a good guide for future landing site analysis or in choosing a specific location for further research., Comment: Accepted for publication in Icarus (arXiv version is Review 1, final version will be online soon on Icarus website)

Mars exploration motivates the search for extraterrestrial life, the development of space technologies, and the design of human missions and habitations. Here we seek new insights and pose unresolved questions relating to the natural history of Mars, habitability, robotic and human exploration, planetary protection, and the impacts on human society. Key observations and findings include:(1)high escape rates of early Mars' atmosphere, including loss of water, impact present-day habitability;(2)putative fossils on Mars will likely be ambiguous biomarkers for life;(3)microbial contamination resulting from human habitation is unavoidable;(4)based on Mars' current planetary protection category, robotic payload(s) should characterize the local martian environment for any life-forms prior to human habitation. Some of the outstanding questions are:(1)which interpretation of the hemispheric dichotomy of the planet is correct;(2)to what degree did deep-penetrating faults transport subsurface liquids to Mars' surface;(3)in what abundance are carbonates formed by atmospheric processes;(4)what properties of martian meteorites could be used to constrain their source locations;(5)the origin(s) of organic macromolecules;(6)was/is Mars inhabited;(7)how can missions designed to uncover microbial activity in the subsurface eliminate potential false positives caused by microbial contaminants from Earth;(8)how can we ensure that humans and microbes form a stable and benign biosphere;(9)should humans relate to putative extraterrestrial life from a biocentric viewpoint (preservation of all biology), or anthropocentric viewpoint of expanding habitation of space? Studies of Mars' evolution can shed light on the habitability of extrasolar planets. In addition, Mars exploration can drive future policy developments and confirm (or put into question) the feasibility and/or extent of human habitability of space.

Joint evaluation of different meteor observation types support the better understanding of both the meteor phenomenon and the terrestrial atmosphere. Two types of examples are presented in this work, linking ionospheric effects to specific meteors, where almost one third of the meteors emerged at high altitudes were simultaneously recorded with an optical camera. Very few such observations have been realized yet. With a daytime fireball, the recorded infrasound effect and the atmospheric blast produced shock wave related small earthquakes were identified by a network of ground stations. The overview of these observational types highlights specific topics where substantial improvements and discoveries are expected in the near future., Comment: Accepted for publication in MNRAS

Martian subsurface habitability and astrobiology can be evaluated via a lava tube cave, without drilling. MACIE addresses two key goals of the Decadal Survey (2013-2022) and three MEPAG goals. New advances in robotic architectures, autonomous navigation, target sample selection, and analysis will enable MACIE to explore the Martian subsurface., Comment: This paper was submitted to the Planetary and Astrobiology Decadal Survey in August 2020

Understanding the origin and evolution of the lunar volatile system is not only compelling lunar science, but also fundamental Solar System science. This white paper (submitted to the US National Academies' Decadal Survey in Planetary Science and Astrobiology 2023-2032) summarizes recent advances in our understanding of lunar volatiles, identifies outstanding questions for the next decade, and discusses key steps required to address these questions.

The Special Collection of papers in this issue of Astrobiology provide an overview of the characteristics and potential for future exploration of the Ojos del Salado volcano, located in the Andes Mountains in front of the Atacama Desert in northern Chile. The main benefits of this site compared with others are the combination of strong UV radiation, the presence of permafrost, and geothermal activity within a dry terrain. The interaction between limited snow events and wind results in snow patches buried under a dry soil surface. This leads to ephemeral water streams that only flow duringdaytime hours. On this volcano, which has the highest located subsurface temperature monitoring systems reported to date, seasonal melting of the permafrost is followed by fast percolation events. This is due to the high porosity of these soils. The results are landforms that shaped by the strong winds. At this site, both thermal springs and lakes (the latter arising from melting ice) provide habitats for life; a 6480m high lake heated by volcanic activity shows both warm and cold sediments that contain a number of different microbial species, including psychrophiles. Where the permafrost melts, thawing ponds have formed at 5900m that is dominated by populations of Bacteroidetes and Proteobacteria, while in the pond sediments and the permafrost itself Acidobacteria, Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and Verrucomicrobia are abundant. In turn, fumaroles show the presence of acidophilic iron-oxidizers and iron-reducing species. In spite of the extreme conditions reported at Ojos del Salado, this site is easily accessible., Comment: Accepted in Astrobiology Special Issue 2020. 04. 10

In this work the potential mineral identification of meteorites is analysed for the mid-infrared range, to evaluate observational possibilities for future missions targeting small body surfaces. Three carbonaceous and three ordinary chondrite meteorites are examined by a diffuse reflection (DRIFT) instrument, and the presence of principal minerals is confirmed by a powder diffraction method as well. The possibilities and constraints of mineral identifications in the mid-infrared are simulated by artificially degrading the spectral resolution. Our research shows that for the definite identification of principal mineral bands, a spectral resolution $\leq 10$~cm$^{-1}$ ($\leq 0.15 \mu$m) is needed. At 20-100~cm$^{-1}$ (0.3 - 1.5~$\mu$m) resolution the identification of these minerals is uncertain, and with a resolution $>100$~cm$^{-1}$, it is almost impossible., Comment: Accepted in MNRAS for publication on May 22nd, 2020; 7 pages, 3 figures

Liquid water is one of the key elements in the search for possible life outside of the Earth and has a wide range of consequences on various chemical and geological processes. The InSight probe landed on Mars with a special equipment dedicated to examine geophysical characteristics and internal heat flow of the planet and some meteorological instruments also included in the payload. We examine the annual and daily variations of near-surface relative humidity and surface temperature calculated from the General Circulation Model (GCM) at Elysium Planitia, the landing site of InSight and search for possible ideal times for deliquescence. We inspect three different hygroscopic salts, but find that out of the three only calcium-perchlorate could liquify at the environment of InSight. We find that nighttime ideal periods could occur in a limited window between approximately Ls 90 and 150 at the late evening hours centered around 9 PM. In our daily studies we find no instances where the whole night could be ideal for deliquescence. This is mostly due to the temperatures dropping below eutectic level leading to a 0.5 - 2 hour long presumed ideal period before midnight. On multiple occasions the temperature is just a few degrees below the necessary limit while relative humidity is high enough, therefore the precise temperature measurements of InSight could be critical in determining ideal periods for deliquescence.

In keeping with the Luxembourg government's initiative to support the future use of space resources, ASIME 2018 was held in Belval, Luxembourg on April 16-17, 2018. The goal of ASIME 2018: Asteroid Intersections with Mine Engineering, was to focus on asteroid composition for advancing the asteroid in-space resource utilisation domain. What do we know about asteroid composition from remote-sensing observations? What are the potential caveats in the interpretation of Earth-based spectral observations? What are the next steps to improve our knowledge on asteroid composition by means of ground-based and space-based observations and asteroid rendez-vous and sample return missions? How can asteroid mining companies use this knowledge? ASIME 2018 was a two-day workshop of almost 70 scientists and engineers in the context of the engineering needs of space missions with in-space asteroid utilisation. The 21 Questions from the asteroid mining companies were sorted into the four asteroid science themes: 1) Potential Targets, 2) Asteroid-Meteorite Links, 3) In-Situ Measurements and 4) Laboratory Measurements. The Answers to those Questions were provided by the scientists with their conference presentations and collected by A. Graps or edited directly into an open-access collaborative Google document or inserted by A. Graps using additional reference materials. During the ASIME 2018, first day and second day Wrap-Ups, the answers to the questions were discussed further. New readers to the asteroid mining topic may find the Conversation boxes and the Mission Design discussions especially interesting., Comment: Outcome from the ASIME 2018: Asteroid Intersections with Mine Engineering, Luxembourg. April 16-17, 2018. 65 Pages. arXiv admin note: substantial text overlap with arXiv:1612.00709

We investigate the global seasonal variations of near-surface relative humidity and relevant attributes, like temperature and water vapor volume mixing ratio on Mars using calculations from modelled and measurement data. We focus on 2 am local time snapshots to eliminate daily effects related to differences in insolation, and to be able to compare calculations based on modelling data from the LMDZ GCM with the observations of MGS TES. We study the seasonal effects by examining four specific dates in the Martian year, the northern spring equinox, summer solstice, autumn equinox and winter solstice. We identify three specific zones, where the near-surface relative humidity levels are systematically higher than in their vicinity regardless of season. We find that these areas coincide with low thermal inertia features, which control surface temperatures on the planet, and are most likely covered with unconsolidated fine dust with grain sizes less than $\sim$ 40$\mu$m. By comparing the data of relative humidity, temperature and water vapor volume mixing ratio at two different heights (near-surface, $\sim$ 23 m above the surface), we demonstrate that the thermal inertia could play an important role in determining near-surface humidity levels. We also notice that during the night the water vapor levels drop at $\sim$ 4 m above the surface. This, together with the temperature and thermal inertia values, shows that water vapor likely condenses in the near-surface atmosphere and on the ground during the night at the three aforementioned regions. This condensation may be in the form of brines, wettening of the fine grains or deliquescence. This study specifies areas of interest on the surface of present day Mars for the proposed condensation, which may be examined by in-situ measurements in the future., Comment: 25 pages, 20 figures, revision under review in Icarus

In addition to long-lived radioactive nuclei like U and Th isotopes, which have been used to measure the age of the Galaxy, also radioactive nuclei with half-lives between 0.1 and 100 million years (short-lived radionuclides, SLRs) were present in the early Solar System (ESS), as indicated by high-precision meteoritic analysis. We review the most recent meteoritic data and describe the nuclear reaction processes responsible for the creation of SLRs in different types of stars and supernovae. We show how the evolution of radionuclide abundances in the Milky Way Galaxy can be calculated based on their stellar production. By comparing predictions for the evolution of galactic abundances to the meteoritic data we can build up a time line for the nucleosynthetic events that predated the birth of the Sun, and investigate the lifetime of the stellar nursery where the Sun was born. We then review the scenarios for the circumstances and the environment of the birth of the Sun within such a stellar nursery that have been invoked to explain the abundances in the ESS of the SLRs with the shortest lives - of the order of million years or less. Finally, we describe how the heat generated by radioactive decay and in particular by the abundant 26Al in the ESS had important consequences for the thermo-mechanical and chemical evolution of planetesimals, and discuss possible implications on the habitability of terrestrial-like planets. We conclude with a set of open questions and future directions related to our understanding of the nucleosynthetic processes responsible for the production of SLRs in stars, their evolution in the Galaxy, the birth of the Sun, and the connection with the habitability of extra-solar planets., Comment: Review published in Progress in Particle and Nuclear Physics. The article is being published Open Access, access to the full article is not restricted in any way. Please download the final version of the paper at https://doi.org/10.1016/j.ppnp.2018.05.002