| 1. |
- Amini, Kasra, et al.
(författare)
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Design of a set of habitat units and the corresponding surrounding cluster for long-term scientific missions in the pre-terraforming era on mars
- 2022
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 385, s. 115119-
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Tidskriftsartikel (refereegranskat)abstract
- We are living in a point in the history of science and technology, where space travel for research and settlement is inevitable. As the utmost crucial technology pieces for leaving Earth and travelling into the cosmos is being established one after another, it is just a matter of decades, until it all gets integrated together, solving the engineering problems ahead of the way and being able to step on the planets and moons of the solar system. In this quest, as has been the case for most of the technological advancements so far, there ought to be mind experiments, in which one skips one step, assumes the availability of responses to the skipped-over step, and searches for the solution to the questions of the next level. This way, by getting passed the first, i.e. current step, the solution to the next one is already available. The current manuscript is addressing this very 'next step', on the long path to eventually colonize Mars and inhabit it for long-term research-based missions; let it be for terraforming, or other agenda to be defined by the research strategists, then. And as mentioned earlier, the current step; being setting foot on Mars, is well-deservedly taken for granted, as is to come forth undoubtedly. Having that realized, we might find ourselves faced by the engineering complexities of surviving and thriving on Mars, which is the subject matter of the current research, from the aspect point of space technological and architectural design. The design procedure beginning from setting the philosophy of design upon the concerns of sustaining in the hostile environment of Mars, to the stepwise emergence of the final design of a cluster of Martian Habitat Units (MHUs) considering the high-criteria of the case, is the subject matter covered in this manuscript.
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| 2. |
- Attree, Nicholas, et al.
(författare)
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Gas flow in Martian spider formation
- 2021
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- Martian araneiform terrain, located in the Southern polar regions, consists of features with central pits and radial troughs which are thought to be associated with the solid state greenhouse effect under a CO2 ice sheet. Sublimation at the base of this ice leads to gas buildup, fracturing of the ice and the flow of gas and entrained regolith out of vents and onto the surface. There are two possible pathways for the gas: through the gap between the ice slab and the underlying regolith, as proposed by Kieffer (2007), or through the pores of a permeable regolith layer, which would imply that regolith properties can control the spacing between adjacent spiders, as suggested by Hao et al. (2019). We test this hypothesis quantitatively in order to place constraints on the regolith properties. Based on previously estimated flow rates and thermophysical arguments, we suggest that there is insufficient depth of porous regolith to support the full gas flow through the regolith. By contrast, free gas flow through a regolith–ice gap is capable of supplying the likely flow rates for gap sizes on the order of a centimetre. This size of gap can be opened in the centre of a spider feature by gas pressure bending the overlying ice slab upwards, or by levitating it entirely as suggested in the original Kieffer (2007) model. Our calculations therefore support at least some of the gas flowing through a gap opened between the regolith and ice. Regolith properties most likely still play a role in the evolution of spider morphology, by regolith cohesion controlling the erosion of the central pit and troughs, for example.
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| 3. |
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| 4. |
- Dalla Pria, Gaia Lucrezia, et al.
(författare)
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Experimental study on the radiation-induced destruction of organic compounds on the surface of the Moon
- 2024
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 415
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Tidskriftsartikel (refereegranskat)abstract
- Volatile organic molecules and a complex organic refractory material were detected on the Moon and on lunar samples. The Moon’s surface is exposed to a continuous flux of solar UV photons and fast ions, e.g. galactic cosmic rays (GCRs), solar wind (SW), and solar energetic particles (SEPs), that modify the physical and chemical properties of surface materials, thus challenging the survival of organic compounds. With this in mind, the aim of this work is to estimate the lifetime of organic compounds on the Moon’s surface under processing by energetic particles. We performed laboratory experiments to measure the destruction cross section of selected organic compounds, namely methane (CH4), formamide (NH2CHO), and an organic refractory residue, under simulated Moon conditions. Volatile species were deposited at low temperature (17 - 18 K) and irradiated with energetic ions (200 keV) in an ultra-high vacuum chamber. The organic refractory residue was produced after warming up of a CO:CH4 ice mixture irradiated with 200 keV H+ at 18 K. All the samples were analyzed in situ by infrared transmission spectroscopy. We found that destruction cross sections are strongly affected (up to one order of magnitude) by the dilution of a given organic in an inert matrix. Among the selected samples, organic refractory residues are the most resistant to radiation. We estimated the lifetime of organic compounds on the surface of the Moon by calculating the dose rate due to GCRs and SEPs at the Moon’s orbit and by using the experimental cross section values. Taking into account impact gardening, we also estimated the fraction of surviving organic material as a function of depth. Our results are compatible with the detection of CH4 in the LCROSS eject plume originating from layers deeper than about 0.7 m at the Moon’s South Pole and with the identification of complex organic material in lunar samples collected by Apollo 17 mission.
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| 5. |
- DeMeo, Francesca E., et al.
(författare)
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Isolating the mechanisms for asteroid surface refreshing
- 2023
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 389
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Tidskriftsartikel (refereegranskat)abstract
- Evidence is seen for young, fresh surfaces among Near-Earth and Main-Belt asteroids even though space-weathering timescales are shorter than the age of the surfaces. A number of mechanisms have been proposed to refresh asteroid surfaces on short timescales, such as planetary encounters, YORP spinup, thermal degradation, and collisions. Additionally, other factors such as grain size effects have been proposed to explain the existence of these “fresh-looking” spectra. To investigate the role each of these mechanisms may play, we collected a sample of visible and near-infrared spectra of 477 near-Earth and Mars Crosser asteroids with similar sizes and compositions — all with absolute magnitude H > 16 and within the S-complex and having olivine to pyroxene (ol/(ol+opx)) ratios >0.65. We taxonomically classify these objects in the Q (fresh) and S (weathered) classes. We find four trends in the Q/S ratio: (1) previous work demonstrated the Q/S ratio increases at smaller sizes down to H ≲16, but we find a sharp increase near H∼19 after which the ratio decreases monotonically. (2) in agreement with many previous studies, the Q/S ratio increases with decreasing perihelion distance, and we find it is non-zero for larger perihelia >1.2AU, (3) as a new finding our work reveals the Q/S ratio has a sharp, significant peak near ∼5° orbital inclination, and (4) we confirm previous findings that the Q/S ratio is higher for objects that have the possibility of encounter with Earth and Venus versus those that do not, however this finding cannot be distinguished from the perihelion trend. No single resurfacing mechanism can explain all of these trends, so multiple mechanisms are required. YORP spin-up scales with size, thermal degradation is dependent on perihelion, planetary encounters trend with inclination, perihelion and MOID, noting that asteroid–asteroid collisions are also dependent on inclination. It is likely that a combination of all four resurfacing mechanisms are needed to account for all observational trends.
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| 6. |
- Fedorets, Grigori, et al.
(författare)
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Discovering Earth’s transient moons with the Large Synoptic Survey Telescope
- 2020
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 338
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Tidskriftsartikel (refereegranskat)abstract
- Earth's temporarily-captured orbiters (TCOs) are a sub-population of near-Earth objects (NEOs). TCOs can provide constraints for NEO population models in the 1–10-metre-diameter range, and they are outstanding targets for in situ exploration of asteroids due to a low requirement on Δv. So far there has only been a single serendipitous discovery of a TCO. Here we assess in detail the possibility of their discovery with the upcoming Large Synoptic Survey Telescope (LSST), previously identified as the primary facility for such discoveries. We simulated observations of TCOs by combining a synthetic TCO population with an LSST survey simulation. We then assessed the detection rates, detection linking and orbit computation, and sources for confusion. Typical velocities of detectable TCOs will range from 1∘/day to 50∘/day, and typical apparent V magnitudes from 21 to 23. Potentially-hazardous asteroids have observational characteristics similar to TCOs, but the two populations can be distinguished based on their orbits with LSST data alone. We predict that a TCO can be discovered once every year with the baseline moving-object processing system (MOPS). The rate can be increased to one TCO discovery every two months if tools complementary to the baseline MOPS are developed for the specific purpose of discovering these objects.
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| 7. |
- Freund, Friedemann T., et al.
(författare)
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Stress-activated electric currents in icy planetary bodies : H2O2-doped H2O ices
- 2021
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Ingår i: Icarus. - : Academic Press Inc.. - 0019-1035 .- 1090-2643. ; 358
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Tidskriftsartikel (refereegranskat)abstract
- Planetary satellites such as the Jovian moon Europa and several Kuiper Belt objects (including Pluto) have surfaces consisting largely of H2O ice, which is brittle and behaves as a rock at the low temperatures that prevail in the outer Solar System. Several of those ice-crusted bodies show evidence of tectonic activity indicating high levels of stress. This paper reports on laboratory experiments with pure H2O ice and H2O2–doped H2O ices with H2O2 concentration levels comparable to those in the ices of Europa. Elongated rectangular ice blocks at T = −81 °C [192 K] were stressed at one end to test whether electric currents are generated and capable of flowing down the stress gradient. Pure H2O ice was found to not produce currents above the 10−10 A background level except for occasional transients in the 10−9–10−8 A range during fracture or rapid plastic deformation due to electrons, e’. By contrast, stressing H2O2-doped H2O ices consistently produced electric currents in the 10−7–10−5 A range, due to holes, h•, propagating from the stressed end to the unstressed end. The h• charge carriers are generated by the break-up of peroxy bonds of H2O2 molecules, leading to O−, equivalent to defect electrons or holes h• in the O2− matrix. © 2020
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| 8. |
- Giono, Gabriel, et al.
(författare)
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Io's SO2 atmosphere from HST Lyman-alpha images : 1997 to 2018
- 2021
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Ingår i: Icarus. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0019-1035 .- 1090-2643. ; 359
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Tidskriftsartikel (refereegranskat)abstract
- The atmosphere of Jupiter's volcanic moon Io consists of mainly sulfur dioxide (SO2), and this main constituent has been studied with a variety of observing techniques across many wavelengths over the years. Here we study absorption by SO2 at the hydrogen Ly-alpha line (1216 angstrom) in a large set of images taken by the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST) between 1997 and 2018. An advanced statistical analysis using a Monte-Carlo trial method is applied to derive the SO2 column density from the Ly-alpha intensity, which includes the uncertainties of the used variables such as solar and background flux. Our analysis produces a probability distribution function of the SO2 column density and highlights some short-comings of the observing technique. Most importantly, the HST/STIS images of the surface-reflected Ly-alpha flux are only sensitive to SO2 column densities between similar to 10(15) cm(-2) and similar to 5x10(16) cm(-2) . Due to strong non-linearity in the relationship between the SO2 abundance and the Ly-alpha flux at the low and high values of detected flux, SO2 abundance directly retrieved from the STIS images will generally fall within these boundaries. This explains the relatively low equatorial column density of about 10(16) cm(-2) reported by previous studies using the Ly-alpha images (e.g., Feldman et al., 2000; Feaga et al., 2009) compared to other studies (e.g., Spencer et al., 2005; Tsang et al., 2013; Jessup and Spencer, 2015; Lellouch et al., 2015), where the obtained column density is often 10(17) cm(-2). By assuming a log-normal probability distribution function for the column density, a new estimate of the SO2 column density is then fitted, indirectly accounting for abundances beyond the detectability limits. This method suggests slightly higher equatorial SO2 abundances and much larger upper-limits, revealing that the Ly-alpha observations are in fact consistent with the higher abundances found in other studies. We then investigate the SO2 abundances at three volcanic sites (Loki, Marduk, Thor), where plumes were observed before and where the sensitivity in our images is comparably high. The observations did not reveal transient changes due to local outgassing at any of the three sites. Finally, the heliocentric distance of Io changed from 4.95 AU to 5.45 AU between the observation dates, potentially allowing us to investigate the influence of solar intensity changes on the SO2 column density via surface frost sublimation. However, the derived error bars are significantly larger than the derived variability, preventing any firm conclusion on seasonal changes and local volcanic outgassing.
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| 9. |
- Lagain, Anthony, et al.
(författare)
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Recalibration of the lunar chronology due to spatial cratering-rate variability
- 2024
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 411
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Tidskriftsartikel (refereegranskat)abstract
- Cratering chronologies are used to derive the history of planetary bodies and assume an isotropic flux of impactors over the entire surface of the Moon. The impactor population is largely dominated by near-Earth-objects (NEOs) since ∼3.5 billion years ago. However, lunar impact probabilities from the currently known NEO population show an excess of impacts close to the poles compared to the equator as well as a latitudinal dependency of the approach angle of impactors. This is accompanied by a variation of the impact flux and speed with the distance from the apex due to the synchronicity of the lunar orbit around the Earth. Here, we compute the spatial dependency of the cratering rate produced by such variabilities and recalibrate the lunar chronology. We show that it allows to reconcile the crater density measured at mid-latitudes around the Chang'e-5 landing site with the age of the samples collected by this mission. Our updated chronology leads to differences in model ages of up to 30% compared to other chronology systems. The modeled cratering rate variability is then compared with the distribution of lunar craters younger than ∼1 Ma, 1 Ga and 4 Ga. The general trend of the cratering distribution is consistent with the one obtained from dynamical models of NEOs, thus potentially reflecting a nonuniform distribution of orbital parameters of ancient impactor populations, beyond 3.5 Ga ago, i.e., planetary leftovers and cometary bodies. If the nonuniformity of the cratering rate could be tested elsewhere in the Solar System, the recalibrated lunar chronology, corrected from spatial variations of the impact flux and approach conditions of impactors, could be extrapolated on other terrestrial bodies such as Mercury and Mars, at least over the last 3.5 billion years. The modeled cratering rate presented here has strong implications for interpreting results of the Artemis program, aiming to explore the South Pole of our satellite, in particular when it will come to link the radiometric age of the samples collected in this region and the crater density of the sampled units.
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| 10. |
- Leblanc, F., et al.
(författare)
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Ganymede's atmosphere as constrained by HST/STIS observations
- 2023
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 399
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Tidskriftsartikel (refereegranskat)abstract
- A new analysis of aurora observations of Ganymede's atmosphere on the orbital leading and trailing hemispheres has been recently published by Roth et al. (2021), suggesting that water is its main constituent near noon. Here, we present two additional aurora observations of Ganymede's sub-Jovian and anti-Jovian hemispheres, which suggest a modulation of the atmospheric H2O/O-2 ratio on the moon's orbital period, and analyze the orbital evolution of the atmosphere. For this, we propose a reconstruction of aurora observations based on a physical modelling of the exosphere taking into account its orbital variability (the Exospheric Global Model; Leblanc et al., 2017). The solution described in this paper agrees with Roth et al. (2021) that Ganymede's exosphere should be dominantly composed of water molecules. From Ganymede's position when its leading hemisphere is illuminated to when it is its trailing hemisphere, the column density of O-2 may vary between 4.3 x 10(14) and 3.6 x 10(14) cm(-2) whereas the H2O column density should vary between 5.6 x 10(14) and 1.3 x 10(15) cm(-2). The water content of Ganymede's atmosphere is essentially constrained by its sublimation rate whereas the O-2 component of Ganymede's atmosphere is controlled by the radiolytic yield. The other species, products of the water molecules, vary in a more complex way depending on their sources, either as ejecta from the surface and/or as product of the dissociation of the other atmospheric constituents. Electron impact on H2O and H-2 molecules is shown to likely produce H Lyman-alpha emissions close to Ganymede, in addition to the observed extended Lyman-alpha corona from H resonant scattering. All these conclusions being highly dependent on our capability to accurately model the origins of the observed Ganymede auroral emissions, modelling these emissions remains poorly constrained without an accurate knowledge of the Jovian magnetospheric and Ganymede ionospheric electron populations.
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