Characterization of dust activity on Mars from MY27 to MY32 by PFS-MEX observations

We present spatial and temporal distributions of dust on Mars from Ls = 331 in MY26 until Ls = 80 in MY33 retrieved from the measurements taken by the Planetary Fourier Spectrometer (PFS) aboard Mars Express. In agreement with previous observations, large dust opacity is observed mostly in the southern hemisphere spring/summer and particularly over regions of higher terrain and large topographic variation. We present a comparison with dust opacities obtained from Thermal Emission Spectrometer (TES) - Mars Global Surveyor (MGS) measurements. We found good consistency between observations of two instruments during overlapping interval (Ls = 331 in MY26 until Ls = 77 in MY27). We found a different behavior of the dust opacity with latitude in the various Martian years (inter-annual variations). A global dust storm occurred in MY28. We observe a different spatial distribution, a later occurrence and dissipation of the dust maximum activity in MY28 than in other Martian years. A possible precursor signal to the global dust storm in MY 28 is observed at Ls = 200 - 235 especially over west Hellas. Heavy dust loads alter atmospheric temperatures. Due to the absorption of solar radiation and emission of infrared radiation to space by dust vertically non-uniformly distributed, a strong heating of high atmospheric levels (40 - 50 km) and cooling below around 30 km are observed.Comment: in press in Icarus. 47 pages, 15 figure

Daily dust variation from the PFS MEx observations

We collected over 7 Martian years (MY) of data observed by the Planetary Fourier Spectrometer (PFS) to present a daily variation of dust content in the Martian atmosphere. We found three typical behaviors of dust opacities with LT (local time). The most peculiar variation was observed when global dust storms (MYs 28 and 34) or particularly strong regional storms (MY 29) occurred on Mars. Here, large dust opacities were measured at 10 LT (MY 34) and 11 LT (MY 28). Then, relatively small values of dust opacities were found in the evening (20 LT). The non-dusty season, particularly near northern summer solstice, was characterized by a deep minimum of the total dust opacity at late night/early morning, while small variations around the mean value were observed during daytime. The clear trend of dust was observed over both hemispheres during early morning. We noted elevated dust opacities in the second half of the year compared to the non-dusty season in all Martian years without global dust storms. The daily variation of three types of storms occurring in moderately dusty conditions was also investigated. Dust in A storms was present in the atmosphere at all LTs and was mostly confined to the southern hemisphere. The maximum of dust opacities in B storms was found at 15–17 LT, close to the South Pole. C storms were mainly constrained to southern latitudes and occurred from the late morning to midday

Vertical temperature profiles in the Venus mesosphere obtained by two retrieval methods from the VIRTIS-VEX observations

We present vertical temperature profiles derived by two different retrieval methods from nighttime radiation measurements performed by VIRTIS(M)-VEx (Visible and Infrared Thermal Imaging Spectrometer, M channel-Venus Express). The Bayesian approach to the optimal estimation method and the relaxation method are applied in this study. This is a first attempt to present and compare results obtained from two independent methods. It allows us to be more convinced of our interpretation. After comparison of temperature profiles we conclude that both retrieval methods are able to sound the atmospheric layers higher than 59 km (In our conclusion we have no preference for any approach. Two methodologies are of equivalent value. Both methods resolve temperature inversions at high altitudes (∼84 km), the quality of fits for all observations is equally well. Only for the Bayesian approach, the retrieval uncertainty above 62 km up to 95 km is less than 2 K. A disadvantage of this method is the time-consuming calculation of weighting functions. The atmospheric temperatures over the "cold collar" region located at 60°S-75°S (60-70 km) are ∼10 K smaller than for latitudes poleward of 75°S (polar region). The cold collar region is seen very clearly in our results for both methods

Similarities and Differences of Global Dust Storms in MY 25, 28, and 34

To better understand the dust cycle on Mars during years with planet-encircling dust storms, we analyze the last three events that took place in Mars Year (MY) 25, MY 28, and MY 34. Global dust storms that occurred in MY 25 and MY 34 (June 2018) were taking place during equinox, while the MY 28 storm had an onset after perihelion. Before the expansion phase of the MY 25 and MY 34 storms, we find similar regions (northern rim of Hellas, Arabia Terra, and Utopia Planitia) where dust is present. Possible precursor dust storms over Hellas and the southern polar cap edges were observed during MY 28 as a component of background dust activity. These features are not found in equinoctial dust storms on this scale. Dust during the MY 25 and MY 34 storms encircled the entire planet by the similar season (Ls = 193°). The MY 34 storm is characterized by a shorter decay phase compared to the events in MY 25 and MY 28. Dust opacity is correlated with atmospheric temperatures at 0.5 mbar and nighttime surface temperatures, while daytime surface temperatures are anticorrelated with dust opacity

PFS/MEX limb observations of 4.3-μm CO2 non-LTE emission in the atmosphere of Mars

We present PFS-MEX limb observations of the CO2 non-local thermodynamic equilibrium (non-LTE) emission at 4.3 μm in the atmosphere of Mars collected in more than six Martian years. With unprecedented spatial and temporal coverage, and relatively high spectral resolution, this unique dataset promises to improve our understanding of the upper atmosphere of Mars. The former allows analyses of the emission as a function of tangent altitude, solar zenith angle, season, latitude, local time, and thermal condition of the atmosphere. The latter allows unambiguous identification of several emission bands of different isotopologues. We selected observations in the altitude range 50-200 km. No emission was detected for altitudes higher than 170 km. The spectral shape of the non-LTE emission changes dramatically with the altitude of the tangent point, reflecting the different contribution of the major and minor CO2 bands and isotopologues to the total emission at different heights. For altitudes higher than 130 km the observed spectrum is dominated by the second hot (SH) bands of the main isotopologue 12C16O2 (also referred to as 626 SH). At lower altitudes, the contribution of the isotopic 13C16O2 second hot bands (636 SH) to the observed spectrum gradually increases, and is maximum around 70-80 km. Similar consideration apply to the fourth hot bands of the 12C16O2 (626 FRH), and particularly those from the (2001x) levels, whose contribution is maximum around 80-90 km. The 626 SH bands can be observed up to an altitude 160-170 km, and their emission is peaked around 120-130 km. The 626 FRH and 636 SH bands are not observed above 130-140 km. Both the first hot (FH) and the fundamental band (FB) of the main isotopologue show a peculiar behavior. Indeed, these emissions can be observed at all altitudes, from 50 km up to 170 km. The intensity of the FH band increases linearly with decreasing height, while the intensity of the FB band is essentially constant at all altitudes, and rapidly decreases above 150 km. For a fixed altitude, the solar zenith angle (SZA) is the main parameter affecting the intensity and the spectral shape of the non-LTE emission. For SZA between 0 and 40° the intensity of the emission does not show significant variations. For SZAs larger than 40° the observed emission decreases rapidly with increasing SZA, following a cosine-like relation. The different illumination also affects the spectral shape of the non-LTE emission spectrum. High incidence angles tend to increase the relative contribution of weaker bands compared to stronger/optically thicker bands. For a fixed SZA, we found variation of the intensity of the emission with local time, in response to variations of the thermal structure of the atmosphere. Latitudinal variation of the intensity of the CO2 non-LTE are also investigated. The maximum intensity is observed around the sub-solar latitudes, where the solar flux is maximum. The intensity of the emission and the altitude at which the maximum emission is observed also changes with the season. The altitude where the maximum intensity of the 626 SH bands is observed decreases from 120-130 km at the perihelion (Ls = 251°), down to ∼85 km at the southern winter solstice (Ls = 90°). This is explained by the variability of the thermal structure (scale heights) of the Martian atmosphere with the season, as a response to the changing solar flux. The altitude of a given pressure level depends on the thermal structure of the atmosphere which, in turn, depends on the season. On the contrary, the pressure level of the peak emission does not depend on the scale heights, as it is mainly controlled by the CO2 column density above the peak. These results, while on one hand confirm and provide more insights and constraints to some aspects of the non-LTE processes on Mars, on the other hand further stimulate and challenge current theoretical models, possibly bringing closer the moment in which the measurements could be inverted to derive important information about the upper mesosphere and lower thermosphere of Mars

Mesospheric CO2 ice clouds on Mars observed by Planetary Fourier Spectrometer onboard Mars Express

We have investigated mesospheric CO2 ice clouds on Mars through analysis of near-infrared spectra acquired by Planetary Fourier Spectrometer (PFS) onboard the Mars Express (MEx) from MY 27 to MY 32. With the highest spectral resolution achieved thus far in the relevant spectral range among remote-sensing experiments orbiting Mars, PFS enables precise identification of the scattering peak of CO2 ice at the bottom of the 4.3 μm CO2 band. A total of 111 occurrences of CO2 ice cloud features have been detected over the period investigated. Data from the OMEGA imaging spectrometer onboard MEx confirm all of PFS detections from times when OMEGA operated simultaneously with PFS. The spatial and seasonal distributions of the CO2 ice clouds detected by PFS are consistent with previous observations by other instruments. We find CO2 ice clouds between Ls = 0° and 140° in distinct longitudinal corridors around the equatorial region (± 20°N). Moreover, CO2 ice clouds were preferentially detected at the observational LT range between 15-16 h in MY 29. However, observational biases prevent from distinguishing local time dependency from inter-annual variation. PFS also enables us to investigate the shape of mesospheric CO2 ice cloud spectral features in detail. In all cases, peaks were found between 4.240 and 4.265 μm. Relatively small secondary peaks were occasionally observed around 4.28 μm (8 occurrences). These spectral features cannot be reproduced using our radiative transfer model, which may be because the available CO2 ice refractive indices are inappropriate for the mesospheric temperatures of Mars, or because of the assumption in our model that the CO2 ice crystals are spherical and composed by pure CO2 ice

Preliminary analysis of PFS/MEx observations of Comet Siding Spring

On October 19th 2014, Mars experienced a close encounter with Comet C/2013 A1 (Siding Spring), at a distance of 138,000 km. We analyze observations by the Planetary Fourier Spectrometer (PFS) onboard Mars Express performed between October 13th and October 21st 2014 to search for spectral signatures of the comet and to investigate possible effects of its passage on the suspended dust and ice content in the Martian atmosphere

12 years of atmospheric monitoring by the Planetary Fourier Spectrometer onboard Mars Express

We use thermal-infrared spectra returned by the Mars Express Planetary Fourier Spectrometer (PFS-MEx) to retrieve atmospheric and surface temperature, and dust and water ice aerosol optical depth. More than 2,500,000 spectra have been used to build this new dataset, covering the full range of season, latitude, longitude, and local time. The data presented here span more than six Martian years (from MY26, Ls = 331°, 10 January 2004 to MY 33, Ls = 78°, 6 December 2015). We successfully retrieved atmospheric temperatures and aerosols opacity in the polar regions, including the polar nights. By exploiting PFS/MEx capability to perform observations at different local times (LT), this dataset allows investigation of the daily cycles of suspended dust and ice. We present an overview of the seasonal and latitudinal dependence of atmospheric quantities during the relevant period, as well as an assessment of the interannual variability in the current Martian climate, including spatial, daily (LT), seasonal, and interannual variations of the aphelion equatorial cloud belt. With unprecedented spatial and temporal coverage and details revealed, this dataset offers new challenges to the GCMs and, at the same time, a new reference for the MYs complementary to those observed by MGS-TES

Mesospheric CO2 ice clouds on Mars observed by Planetary Fourier Spectrometer onboard Mars Express

We investigate mesospheric CO2 ice clouds on Mars detected by the Planetary Fourier Spectrometer (PFS) onboard Mars Express (MEx). The relatively high spectral resolution of PFS allows firm identification of the clouds' reflection spike. A total of 279 occurrences of the CO2 ice clouds features has been detected at the bottom of 4.3 μm CO2 band from the MEx/PFS data during the period from MY27 to MY32. 115 occurrences out of them are also confirmed by simultaneous observations by MEx/OMEGA imaging spectrometer. The spatial and seasonal distributions of the CO2 ice clouds observed by PFS are consistent with the previous studies: the CO2 ice clouds are only observed between Ls=0° and 140° at distinct longitudinal corridors around the equatorial region (±20°N). The CO2 ice clouds are preferentially detected at local time between 15-17h. The relatively high spectral resolution of PFS allows us to investigate the spectral shape of the CO2 ice clouds features. The CO2 ice clouds reflection spike is peaked between 4.24 and 4.29 μm, with no evidence of the secondary peak at 4.32-4.34 μm observed by MEx/OMEGA (Määttänen et al., 2010). In most of the cases (about 75%), the peak is present between 4.245 and 4.255 μm. Moreover, small secondary peaks are found around 4.28 μm (about 15 occurrences). These spectral features cannot be reproduced by the synthetic spectra with the assumption of a spherical particle shape in our radiative transfer model (DISORT). This can be due to the fact that the available CO2 ice reflective indexes are either inaccurate or inappropriate for the mesospheric temperatures, or that the particle shape is not spherical. Accurate measurements of the reflective index depending on temperature and detailed comparison with the model taking into account non-spherical shapes will give a clue to solve this issue

The Phase A study of the ESA M4 mission candidate ARIEL

© 2018, The Author(s). ARIEL, the Atmospheric Remote sensing Infrared Exoplanet Large survey, is one of the three M-class mission candidates competing for the M4 launch slot within the Cosmic Vision science programme of the European Space Agency (ESA). As such, ARIEL has been the subject of a Phase A study that involved European industry, research institutes and universities from ESA member states. This study is now completed and the M4 down-selection is expected to be concluded in November 2017. ARIEL is a concept for a dedicated mission to measure the chemical composition and structure of hundreds of exoplanet atmospheres using the technique of transit spectroscopy. ARIEL targets extend from gas giants (Jupiter or Neptune-like) to super-Earths in the very hot to warm zones of F to M-type host stars, opening up the way to large-scale, comparative planetology that would place our own Solar System in the context of other planetary systems in the Milky Way. A technical and programmatic review of the ARIEL mission was performed between February and May 2017, with the objective of assessing the readiness of the mission to progress to the Phase B1 study. No critical issues were identified and the mission was deemed technically feasible within the M4 programmatic boundary conditions. In this paper we give an overview of the final mission concept for ARIEL as of the end of the Phase A study, from scientific, technical and operational perspectives. ispartof: Experimental Astronomy vol:46 issue:1 pages:211-239 status: publishe