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Studies, e.g. [1,2], reveal that the South-Pole Aitken (SPA) basin is unique, particularly because it is the deepest basin on the Moon and might be expected to expose the lunar mantle [3]. The innermost part of SPA is rich in high Ca-pyroxenes, except for some central crater peaks, where low Ca-pyroxenes dominate. No extensive olivine-rich areas are observed, implying a mantle rich in low Ca-pyroxenes instead of olivine [1, 3, 4]. Furthermore, thorium anomalies have been discovered in two craters within Aitken basin [5]. Here, we focus on the spectral analysis of one of the most interesting impact crater inside SPA, the Apollo basin. Recently, [6] published a detailed geological map of the area surrounding Apollo basin (35.69°S, 151.48°W; D~524 km), using morphology, stratigraphy, crater size-frequency distribution measurements, and Clementine spectral data to define the unit. Our work explores data from the M3 imaging spectrometer onboard Chandrayaan-1 [7] for this region. These analyses are part of the PLANMAP project, and the integration of the spectroscopical information with the results from [6] will permit to produce highly informative geological maps of the Moon [8]. This work is funded by the European Union's Horizon 2020 research grant agreement No 776276- PLANMAP. References [1] Ohtake, M. et al., 2014, GRL. [2] Moriarty, D.P. et al., 2018, JGR. [3] Dhingra, D., 2018, Geosciences. [4] Melosh, H. J., et al., 2017, Geology. [5] Lawrence, D.J. et al., 2000, JGR. [6] Ivanov, M.A., 2018, JGR. [7] Pieters et al., 2009, Current Science [8] https://www.planmap.eu/

Studies, e.g. (Ohtake et al., 2014, Moriarty and Pieters, 2018), reveal that the South-Pole Aitken (SPA) basin is unique, particularly because it is the deepest basin on the Moon and might be expected to expose the lunar mantle (Dhingra et al., 2018). The innermost part of SPA is rich in high Ca-pyroxenes, except for some central crater peaks, where low Ca-pyroxenes dominate. No extensive olivine-rich areas are observed, implying a mantle rich in low Ca-pyroxenes instead of olivine (Ohtake et al., 2014, Dhingra et al., 2018, Melosh et al., 2018). Furthermore, thorium anomalies have been discovered in two craters within Aitken basin (Lawrence et al., 2000). Here, we focus on the spectral analysis of one of the most interesting impact crater inside SPA, the Apollo basin. Recently, Ivanov et al., (2018) published a detailed geological map of the area surrounding Apollo basin (35.69°S, 151.48°W; D~524 km), using morphology, stratigraphy, crater size- frequency distribution measurements, and Clementine spectral data to define the unit. Our work explores data from the M3 imaging spectrometer onboard Chandrayaan-1 (Pieters et al., 2009) for this region. A preliminary analysis of Apollo basin emphasizes a spectral variability between the smooth terrains within the floor and rest of the crater. The smooth terrains appear darker and show a clear compositional variation with respect to the surroundings regions, indicating the presence of other mineralogical phases mixed with pyronexes, and/or a different geological context. These study is part of the PLANMAP project, and the integration of the spectroscopical information with the results from Ivanov, et al., (2018) will permit to produce highly informative geological maps of the Moon (https://www.planmap.eu/). This work is funded by the European Union's Horizon 2020 research grant agreement No 776276- PLANMAP. References [1] Ohtake, M. et al., 2014. Geologic structure generated by large-impact basin formation observed at the South Pole-Aitken basin on the Moon. Geophysical ...

H05 Hokusai (22.5°N–65°N, 0°–90°E) is one of the northern quadrangles of Mercury [1, 2]. It is characterized by different features, and includes several morpho-stratigraphic units. Smooth plains is the most widespread, covering ~43% of the entire quadrangle, followed by fresh crater material (~17%) and intercrater plains (~10%). The remaining part of the quadrangle contains intermediate plains (7%), degraded crater material (9%) and heavily degraded material (8%) [1]. Other morpho-stratigraphic units, such as smooth and hummocky crater floor material, account for a few percent [1]. Furthermore, this quadrangle includes part of the Hokusai ray system, the largest example on Mercury, and several pyroclastic deposits, including Nathair Facula, one of the highest-reflectance features observed on the planet, located at 480 km NE of Rachmaninoff crater [3, 4]. Spectral analysis based on specific spectral parameters represents a suitable approach to investigate compositional variations. We observed different spectral behavior among large parts of the morpho-stratigraphic units and surface features mapped by [1]. In particular, the units that show the highest spectral variability are the intermediate plains, smooth plains and fresh crater material, together with pyroclastic deposits and crater rays. Such a result indicates spectral variation related to the different units with implications for the geological processes on Mercury's surface. This work is funded by the European Union's Horizon 2020 research grant agreement No 776276- PLANMAP and by the Italian Space Agency (ASI) within the SIMBIO-SYS project (ASI-INAF agreement 2017-47-H.0). References [1] Wright et al., 2018, LPSC 2018 [2] https://planetarynames.wr.usgs.gov/Page/mercuryQuadMap [3] Rothery, D. et al., 2018 Oxford Research Encyclopedia of Planetary Science. Ed. [4] Procter, L. et al., 2010, Science 329.

We report on daytime limb observations of Mars upper atmosphere acquired by the OMEGA instrument on board the European spacecraft Mars Express. The strong emission observed at 4.3m is interpreted as due to CO2 fluorescence of solar radiation and is detected at a tangent altitude in between 60 and 110km. The main value of OMEGA observations is that they provide simultaneously spectral information and good spatial sampling of the CO2 emission. In this study we analyzed 98 dayside limb observations spanning over more than 3 Martian years, with a very good latitudinal and longitudinal coverage. Thanks to the precise altitude sounding capabilities of OMEGA, we extracted vertical profiles of the non-local thermodynamic equilibrium (non-LTE) emission at each wavelength and we studied their dependence on several geophysical parameters, such as the solar illumination and the tangent altitude. The dependence of the non-LTE emission on solar zenith angle and altitude follows a similar behavior to that predicted by the non-LTE model. According to our non-LTE model, the tangent altitude of the peak of the CO2 emission varies with the thermal structure, but the pressure level where the peak of the emission is found remains constant at approximate to 0.03 0.01Pa, . This non-LTE model prediction has been corroborated by comparing SPICAM and OMEGA observations. We have shown that the seasonal variations of the altitude of constant pressure levels in SPICAM stellar occultation retrievals correlate well with the variations of the OMEGA peak emission altitudes, although the exact pressure level cannot be defined with the spectroscopy for the investigation of the characteristics of the atmosphere of Venus (SPICAM) nighttime data. Thus, observed changes in the altitude of the peak emission provide us information on the altitude of the 0.03Pa pressure level. Since the pressure at a given altitude is dictated by the thermal structure below, the tangent altitude of the peak emission represents then an important piece of information of the atmosphere, of great value for validating general circulation models. We thus compared the altitude of OMEGA peak emission with the altitude of the 0.03Pa level predicted by the Laboratoire de meteorologie dynamique (LMD)-Mars global circulation model and found that the peak emission altitudes from OMEGA present a much larger variability than the tangent altitude of the 0.03Pa level predicted by the general circulation model. This variability could be possibly due to unresolved atmospheric waves. Further studies using this strong CO2 limb emission data are proposed. ; A.P. acknowledges funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement 246556.This work has received funding from the European Union's Horizon 2020 Programme (H2020-Compet-08-2014) under grant agreement UPWARDS-633127. ; Peer reviewed

NOMAD is a suite of three spectrometers that will be launched in 2016 as part of the joint ESA-Roscosmos ExoMars Trace Gas Orbiter mission. The instrument contains three channels that cover the IR and UV spectral ranges and can perform solar occultation, nadir and limb observations, to detect and map a wide variety of Martian atmospheric gases and trace species. Part I of this work described the models of the UVIS channel; in this second part, we present the optical models representing the two IR channels, SO (Solar Occultation) and LNO (Limb, Nadir and Occultation), and use them to determine signal to noise ratios (SNRs) for many expected observational cases. In solar occultation mode, both the SO and LNO channel exhibit very high SNRs >5000. SNRs of around 100 were found for the LNO channel in nadir mode, depending on the atmospheric conditions, Martian surface properties, and observation geometry. ; NOMAD has been made possible thanks to funding by the Belgian Science Policy Office (BELSPO) and financial and contractual coordination by the ESA Prodex Office. The research was performed as part of the "Interuniversity Attraction Poles" programme financed by the Belgian government (Planet TOPERS). UK funding is acknowledged under the UK Space Agency grant ST/I003061/1. ; Peer Reviewed

A publisher correction to this article was published on 17 April 2019 ; Global dust storms on Mars are rare1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere3, primarily owing to solar heating of the dust3. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars4. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes5,6, as well as a decrease in the water column at low latitudes7,8. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H2O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals3. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere. © 2019, The Author(s), under exclusive licence to Springer Nature Limited. ; This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493); by the Spanish MICINN through its Plan Nacional and by European funds under grants ESP2015-65064-C2-1-P and ESP2017-87143-R (MINECO/FEDER); by the UK Space Agency through grants ST/R005761/1, ST/P001262/1, ST/R001405/1, ST/S00145X/1, ST/R001367/1, ST/P001572/1 and ST/R001502/1; and the Italian Space Agency through grant 2018-2-HH.0. The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the 'Center of Excellence Severo Ochoa' award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709). This work was supported by the Belgian Fonds de la Recherche Scientifique - FNRS under grant number 30442502 (ET_HOME). The ACS experiment is led by IKI, Space Research Institute in Moscow, assisted by LATMOS in France. The project acknowledges funding by Roscosmos and CNES. The science operations of ACS are funded by Roscosmos and ESA. IKI affiliates acknowledge funding under grant number 14.W03.31.0017 and contract number 0120.0 602993 (0028-2014-0004) of the Russian government. ; Peer Reviewed

A publisher correction to this article was published on 17 April 2019 ; The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today1. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations2–5. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere6,7, which—given methane's lifetime of several centuries—predicts an even, well mixed distribution of methane1,6,8. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections2,4. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally. © 2019, The Author(s), under exclusive licence to Springer Nature Limited. ; ExoMars is the space mission of ESA and Roscosmos. The ACS experiment is led by IKI, the Space Research Institute in Moscow, assisted by LATMOS in France. The project acknowledges funding by Roscosmos and CNES. The science operations of ACS are funded by Roscosmos and ESA. IKI affiliates acknowledge funding under grant number 14.W03.31.0017 and contract number 0120.0 602993 (0028-2014-0004) of the Russian government. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), assisted by co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the UK (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination of the ESA Prodex Office (PEA 4000103401 and PEA 4000121493), by Spanish MICINN through its Plan Nacional and by European funds under grants ESP2015-65064-C2-1-P and ESP2017-87143-R (MINECO/FEDER), as well as by the UK Space Agency through grants ST/R005761/1, ST/P001262/1, ST/R001405/1, ST/S00145X/1, ST/R001367/1, ST/P001572/1 and ST/R001502/1, and the Italian Space Agency through grant 2018-2-HH.0. This work was supported by the Belgian Fonds de la Recherche Scientifique-FNRS under grant number 30442502 (ET_HOME). ; Peer Reviewed

NOMAD (Nadir and Occultation for MArs Discovery) is one of the four instruments on board the ExoMars Trace Gas Orbiter, scheduled for launch in March 2016. It consists of a suite of three high-resolution spectrometers - SO (Solar Occultation), LNO (Limb, Nadir and Occultation) and UVIS (Ultraviolet and Visible Spectrometer). Based upon the characteristics of the channels and the values of Signal-to-Noise Ratio obtained from radiometric models discussed in (Vandaele et al., 2015a, 2015b; Thomas et al., 2016), the expected performances of the instrument in terms of sensitivity to detection have been investigated. The analysis led to the determination of detection limits for 18 molecules, namely CO, HO, HDO, CH, CH, CH, HCO, CH, SO, HS, HCl, HCN, HO, NH, NO, NO, OCS, O. NOMAD should have the ability to measure methane concentrations Inter-university Attraction Poles> programme financed by the Belgian Government (Planet TOPERS no P7-15) and a BRAIN Research Grant BR/143/A2/SCOOP. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement no. 607177 CrossDrive. UK funding is acknowledged under the UK Space Agency Grant ST/I003061/1. ; Peer Reviewed