| 41. |
- Moyano-Cambero, Carles E., et al.
(författare)
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Petrographic and geochemical evidence for multiphase formation of carbonates in the Martian orthopyroxenite Allan Hills 84001
- 2017
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Ingår i: Meteoritics and Planetary Science. - : John Wiley & Sons. - 1086-9379 .- 1945-5100. ; 52:6, s. 1030-1047
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Tidskriftsartikel (refereegranskat)abstract
- Martian meteorites can provide valuable information about past environmental conditions on Mars. Allan Hills 84001 formed more than 4 Gyr ago, and owing to its age and long exposure to the Martian environment, and this meteorite has features that may record early processes. These features include a highly fractured texture, gases trapped during one or more impact events or during formation of the rock, and spherical Fe-Mg-Ca carbonates. In this study, we have concentrated on providing new insights into the context of these carbonates using a range of techniques to explore whether they record multiple precipitation and shock events. The petrographic features and compositional properties of these carbonates indicate that at least two pulses of Mg- and Fe-rich solutions saturated the rock. Those two generations of carbonates can be distinguished by a very sharp change in compositions, from being rich in Mg and poor in Fe and Mn, to being poor in Mg and rich in Fe and Mn. Between these two generations of carbonate is evidence for fracturing and local corrosion
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| 42. |
- Nazarious, Miracle Israel, 1992-
(författare)
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Scientific Instruments to Facilitate the Human Exploration of Mars
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis describes, from an engineering perspective, some of the preliminary steps that need to be implemented to facilitate the human exploration of Mars. It focuses on the development of a set of novel scientific or technology demonstrator instruments. The engineering problem starts with a conceptual idea and the definition of individual functional requirements, that may be related to scientific or technological objectives. To solve this problem, an unique approach adapted during this thesis, allowed for designing and building efficiently, testing and refining the instruments in multiple iterations using simple techniques like 3-D printing, breadboard prototyping and low-cost commercial off the shelf (COTS) components. This approach reduces the cost and facilitates the accessibility of space instrument design and testing to a broader community. The steps include demonstrating the operability of the concept with prototypes, calibrating the responses and validating their operation in representative environments, thereby raising the technology readiness level (TRL) of the instrument with a lower investment in time and resources than traditional approaches that use specialized components and fabrica-tion techniques.The thesis provides a detailed description of the design and development process, and discusses the calibration and validation results of four different instruments, namely: 1) Brine Observation Transition To Liquid Experiment (BOTTLE) as a part of HabitAbil-ity: Brines, Irradiation and Temperature (HABIT) instrument onboard the ESA/IKI’s ExoMars 2022 Surface Platform Kazachok, for investigating the surface environmen-tal conditions and demonstrating the capability of salts to absorb water on Mars, 2) Metabolt, a small-sized portable incubator to monitor the behaviour of the microbiome in soils, which will be a critical element of future greenhouses on Mars or the Moon, 3) Methanox, an in-situ resource utilization demonstrator for converting local resources on Mars and producing methane and ammonia as space fuel, and 4) PRessure Optimized PowEred Respirator (PROPER), a wearable cleanroom developed for protecting the hu-mans against biological pathogens, showing the direct applicability of this research to solve Earth-based problems. During the final phase of the PhD thesis, the world suffered the COVID-19 pandemic. This challenge provided an opportunity to test the approach presented in this thesis and inspired the development of this equipment, and may also be of relevance to protect from biological cross-contamination in planetary habitats and laboratories while handling local regolith materials and samples on Mars.This work also highlights the calibration of the HABIT Flight Model (FM) in the cleanroom of Omnisys Instruments AB, Sweden, defines the retrieval models that will be used during ExoMars 2022 mission operations and data archiving in the Planetary Science Archive (PSA). Parts of this thesis were already published in the form of peer-reviewed journal articles and conference abstracts.
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| 43. |
- Orton, Glenn S., et al.
(författare)
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Mid-infrared spectroscopy of Uranus from the Spitzer Infrared Spectrometer : 1. Determination of the mean temperature structure of the upper troposphere and stratosphere
- 2014
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 243, s. 494-513
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Tidskriftsartikel (refereegranskat)abstract
- On 2007 December 16-17, spectra were acquired of the disk of Uranus by the Spitzer Infrared Spectrometer (IRS), ten days after the planet's equinox, when its equator was close to the sub-Earth point. This spectrum provides the highest-resolution broad-band spectrum ever obtained for Uranus from space, allowing a determination of the disk-averaged temperature and molecule composition to a greater degree of accuracy than ever before. The temperature profiles derived from the Voyager radio occultation experiment by Lindal et al. (Lindal, G.F., Lyons, J.R., Sweetnam, D.N., Eshleman, V.R., Hinson, D.P. [1987]. J. Geophys. Res. 92, 14987-15001) and revisions suggested by Sromovsky et al. (Sromovsky, L.A., Fry, P.A., Kim, J.H. [2011]. Icarus 215, 292-312) that match these data best are those that assume a high abundance of methane in the deep atmosphere. However, none of these model profiles provides a satisfactory fit over the full spectral range sampled. This result could be the result of spatial differences between global and low-latitudinal regions, changes in time, missing continuum opacity sources such as stratospheric hazes or unknown tropospheric constituents, or undiagnosed systematic problems with either the Voyager radio-occultation or the Spitzer IRS data sets. The spectrum is compatible with the stratospheric temperatures derived from the Voyager ultraviolet occultations measurements by Herbert et al. (Herbert, F. et al. [1987]. J. Geophys. Res. 92, 15093-15109), but it is incompatible with the hot stratospheric temperatures derived from the same data by Stevens et al. (Stevens, M.H., Strobel, D.F., Herbert, F.H. [1993]. Icarus 101, 45-63). Thermospheric temperatures determined from the analysis of the observed H2 quadrupole emission features are colder than those derived by Herbert et al. at pressures less than ~1μbar. Extrapolation of the nominal model spectrum to far-infrared through millimeter wavelengths shows that the spectrum arising solely from H2 collision-induced absorption is too warm to reproduce observations between wavelengths of 0.8 and 3.3mm. Adding an additional absorber such as H2S provides a reasonable match to the spectrum, although a unique identification of the responsible absorber is not yet possible with available data. An immediate practical use for the spectrum resulting from this model is to establish a high-precision continuum flux model for use as an absolute radiometric standard for future astronomical observations.
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| 44. |
- Orton, Glenn S., et al.
(författare)
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Mid-infrared spectroscopy of Uranus from the Spitzer infrared spectrometer : 2. Determination of the mean composition of the upper troposphere and stratosphere
- 2014
-
Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 243, s. 471-493
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Tidskriftsartikel (refereegranskat)abstract
- Mid-infrared spectral observations Uranus acquired with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope are used to determine the abundances of C2H2, C2H6, CH3C2H, C4H2, CO2, and tentatively CH3 on Uranus at the time of the 2007 equinox. For vertically uniform eddy diffusion coefficients in the range 2200-2600cm2s-1, photochemical models that reproduce the observed methane emission also predict C2H6 profiles that compare well with emission in the 11.6-12.5μm wavelength region, where the υ9 band of C2H6 is prominent. Our nominal model with a uniform eddy diffusion coefficient Kzz=2430cm2s-1 and a CH4 tropopause mole fraction of 1.6×10-5 provides a good fit to other hydrocarbon emission features, such as those of C2H2 and C4H2, but the model profile for CH3C2H must be scaled by a factor of 0.43, suggesting that improvements are needed in the chemical reaction mechanism for C3Hx species. The nominal model is consistent with a CH3D/CH4 ratio of 3.0±0.2×10-4. From the best-fit scaling of these photochemical-model profiles, we derive column abundances above the 10-mbar level of 4.5+01.1/-0.8×1019molecule-cm-2 for CH4, 6.2±1.0×1016molecule-cm-2 for C2H2 (with a value 24% higher from a different longitudinal sampling), 3.1±0.3×1016molecule-cm-2 for C2H6, 8.6±2.6×1013molecule-cm-2 for CH3C2H, 1.8±0.3×1013molecule-cm-2 for C4H2, and 1.7±0.4×1013molecule-cm-2 for CO2 on Uranus. A model with Kzz increasing with altitude fits the observed spectrum and requires CH4 and C2H6 column abundances that are 54% and 45% higher than their respective values in the nominal model, but the other hydrocarbons and CO2 are within 14% of their values in the nominal model. Systematic uncertainties arising from errors in the temperature profile are estimated very conservatively by assuming an unrealistic "alternative" temperature profile that is nonetheless consistent with the observations; for this profile the column abundance of CH4 is over four times higher than in the nominal model, but the column abundances of the hydrocarbons and CO2 differ from their value in the nominal model by less than 22%. The CH3D/CH4 ratio is the same in both the nominal model with its uniform Kzz as in the vertically variable Kzz model, and it is 10% lower with the "alternative" temperature profile than the nominal model. There is no compelling evidence for temporal variations in global-average hydrocarbon abundances over the decade between Infrared Space Observatory and Spitzer observations, but we cannot preclude a possible large increase in the C2H2 abundance since the Voyager era. Our results have implications with respect to the influx rate of exogenic oxygen species and the production rate of stratospheric hazes on Uranus, as well as the C4H2 vapor pressure over C4H2 ice at low temperatures.
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| 45. |
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| 46. |
- Richards, Stephen, et al.
(författare)
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Genome Sequence of the Pea Aphid Acyrthosiphon pisum
- 2010
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Ingår i: PLoS biology. - : Public Library of Science (PLoS). - 1544-9173 .- 1545-7885. ; 8:2, s. e1000313-
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Tidskriftsartikel (refereegranskat)abstract
- Aphids are important agricultural pests and also biological models for studies of insect-plant interactions, symbiosis, virus vectoring, and the developmental causes of extreme phenotypic plasticity. Here we present the 464 Mb draft genome assembly of the pea aphid Acyrthosiphon pisum. This first published whole genome sequence of a basal hemimetabolous insect provides an outgroup to the multiple published genomes of holometabolous insects. Pea aphids are host-plant specialists, they can reproduce both sexually and asexually, and they have coevolved with an obligate bacterial symbiont. Here we highlight findings from whole genome analysis that may be related to these unusual biological features. These findings include discovery of extensive gene duplication in more than 2000 gene families as well as loss of evolutionarily conserved genes. Gene family expansions relative to other published genomes include genes involved in chromatin modification, miRNA synthesis, and sugar transport. Gene losses include genes central to the IMD immune pathway, selenoprotein utilization, purine salvage, and the entire urea cycle. The pea aphid genome reveals that only a limited number of genes have been acquired from bacteria; thus the reduced gene count of Buchnera does not reflect gene transfer to the host genome. The inventory of metabolic genes in the pea aphid genome suggests that there is extensive metabolite exchange between the aphid and Buchnera, including sharing of amino acid biosynthesis between the aphid and Buchnera. The pea aphid genome provides a foundation for post-genomic studies of fundamental biological questions and applied agricultural problems.
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| 47. |
- Siskind, David E., et al.
(författare)
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Decreases in atomic hydrogen over the summer pole : Evidence for dehydration from polar mesospheric clouds?
- 2008
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:13
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Tidskriftsartikel (refereegranskat)abstract
- Observations from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) instrument on the NASA/Thermospheric Ionosphere Mesosphere Energetics and Dynamics satellite show a surprising decrease in the inferred atomic hydrogen (H) over the polar regions in the lowermost thermosphere during the summer. This contrasts with predictions by global models that H should peak in this region at this time. We suggest the decrease is a consequence of the sequestering of the water vapor by the formation of polar mesospheric clouds (PMCs) that redistributes the H2O thus reducing the chemical source of H. This decrease is more pronounced in the Northern rather than the Southern summer which is roughly consistent with the known morphology of PMCs. A model calculation which includes a PMC parameterization gives good qualitative agreement with the data suggesting that this process should be considered in global models of the coupling between the middle and upper atmosphere. Copyright 2008 by the American Geophysical Union.
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| 48. |
- Smith, Anne K., et al.
(författare)
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Satellite observations of high nighttime ozone at the equatorial mesopause
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:17
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Tidskriftsartikel (refereegranskat)abstract
- Measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry instrument enable the characterization of the seasonal variation of ozone and temperature in the upper mesosphere. These are the first global measurements that resolve both the structure of the secondary ozone maximum at night and the temperature over all seasons of the year. The average nighttime mixing ratios at the altitude of the maximum vary with latitude and season. Analysis shows that the highest mixing ratios are clustered near the equator during equinoxes. The high ozone mixing ratios are observed in exactly the place and time at which the diurnal tide is largest. The diurnal tidal phase is such that coldest temperatures at 95 km occur near midnight. The high ozone is coincident with regions that have both low temperature and low amounts of atomic hydrogen. We focus particularly on ozone mixing ratios in the range of 18-50 ppmv; these occur intermittently in the equinoctial tropics on days when the night temperature is particularly cold. The occurrence of ozone maxima over 20 ppmv was unexpected but is shown in this paper to be consistent with theory and is a result of large-amplitude diurnal tides. The same seasonal and latitudinal characteristics are seen in ozone density measured by Global Ozone Monitoring by Occultation of Stars. Copyright 2008 by the American Geophysical Union.
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| 49. |
- Ullán, Aurora, et al.
(författare)
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Analysis of wind-induced dynamic pressure fluctuations during one and a half Martian years at Gale Crater
- 2017
-
Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 288, s. 78-87
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Tidskriftsartikel (refereegranskat)abstract
- The Rover Environmental Monitoring Station (REMS) instrument on-board the Mars Science Laboratory (MSL) has acquired unprecedented measurements of key environmental variables at the base of Gale Crater. The pressure measured by REMS shows modulations with a very structured pattern of short-time scale (of the order of seconds to several minutes) mild fluctuations (typically up to 0.2 Pa at daytime and 1 Pa at night-time). These dynamic pressure oscillations are consistent with wind, air and ground temperature modulations measured simultaneously by REMS. We detect the signals of a repetitive pattern of upslope/downslope winds, with maximal speeds of about 21 m/s, associated with thermal changes in the air and surface temperatures, that are initiated after sunset and finish with sunrise proving that Gale, a 4.5 km deep impact crater, is an active Aeolian environment. At nighttime topographic slope winds are intense with maximal activity from 17:00 through 23:00 Local Mean Solar Time, and simultaneous changes of surface temperature are detected. During the day, the wind modulations are related to convection of the planetary boundary layer, winds are softer with maximum wind speed of about 14 m/s. The ground temperature is modulated by the forced convection of winds, with amplitudes between 0.2 K and 0.5 K, and the air temperatures fluctuate with amplitudes of about 2 K. The analysis of more than one and a half Martian years indicates the year-to-year repeatability of these environmental phenomena. The wind pattern minimizes at the beginning of the south hemisphere winter (Ls 90) season and maximizes during late spring and early summer (Ls 270). The procedure that we present here is a useful tool to investigate in a semi-quantitative way the winds by: i) filling both seasonal and diurnal gaps where wind measurements do not exist, ii) providing an alternative way for comparisons through different measuring principia and, iii) filling the gap of observation of short time-wind variability, where the REMS wind-sensor is blind
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| 50. |
- Webster, Christopher R., et al.
(författare)
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Background levels of methane in Mars' atmosphere show strong seasonal variations
- 2018
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Ingår i: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 360:6393, s. 1093-1096
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Tidskriftsartikel (refereegranskat)abstract
- Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.
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