Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano

Starting in September 2018, a daily repeating extremely elongated cloud was observed extending up to 1800km from the Mars Arsia Mons volcano. We study this Arsia Mons Elongated Cloud (AMEC) using images from VMC, HRSC, and OMEGA on board Mars Express, IUVS on MAVEN, MCC on Mars Orbiter Mission (MOM), MARCI on MRO, and Visible Camera on Viking 2 orbiter. We study the daily cycle of this cloud, showing how the morphology and other parameters of the cloud evolved rapidly with local time. The cloud expands every morning from the western slope of the volcano, at a westward velocity of around 160m/s, and an altitude of around 45km over martian areoid. The expansion starts with sunrise, and resumes around 2.5 hours later, when cloud formationresumes and the elongated tail detaches from the volcano and keeps moving westward until it evaporates before afternoon, when most sun-synchronous missions observe. This daily cycle repeated regularly for at least 80 sols in 2018 (Martian Year 34). We find in images from past years that this AMEC is an annually repeating phenomenon that takes place around the Solar Longitude range 220º-320º. We study the AMEC in Martian Year 34 in terms of Local Time and Solar Longitude, and then compare with observations from previous years, in search for interannual variations, taking into account the possible influence of the recent Global Dust Storm

Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano

Starting in September 2018, a daily repeating extremely elongated cloud was observed extending from the Mars Arsia Mons volcano. We study this Arsia Mons Elongated Cloud (AMEC) using images from VMC, HRSC, and OMEGA on board Mars Express, IUVS on MAVEN, and MARCI on MRO. We study the daily cycle of this cloud, showing how the morphology and other parameters of the cloud evolved with local time. The cloud expands every morning from the western slope of the volcano, at a westward velocity of around 150m/s, and an altitude of around 30-40km over the local surface. Starting around 2.5 hours after sunrise (8.2 Local True Solar Time, LTST), the formation of the cloud resumes, and the existing cloud keeps moving westward, so it detaches from the volcano, until it evaporates in the following hours. At this time, the cloud has expanded to a length of around 1500km. Short time later, a new local cloud appears on the western slope of the volcano, starting around 9.5 LTST, and grows during the morning. This daily cycle repeated regularly for at least 90 sols in 2018, around Southern Solstice (Ls 240-300) in Martian Year (MY) 34. According with these and previous MEx/VMC observations, this elongated cloud is a seasonal phenomenon occurring around Southern Solstice every Martian Year. We study the interannual variability of this cloud, the influence of the Global Dust Storms in 2018 on the cloud’s properties (Sánchez-Lavega et al., Geophys. Res. Lett. 46, 2019), and its validity as a proxy for the global state of the Martian atmosphere (Sánchez-Lavega et al., J. Geophys. Res., 123, 3020, 2018). We discuss the physical mechanisms behind the formation of this peculiar cloud in Mars

Quantifying the latitudinal distribution of climate-related landforms on Mars' southern hemisphere

The focus of this work is to contribute information about possible climate-related environments on Mars from a geomorphological perspective. In order to understand the latitudinal distribution of current and former climatic environments on Mars, we applied the so-called grid-mapping approach in order to quantify the geography of 17 climate-related landforms that each indicates a particular morphoclimate at the time of their evolution. Grid-mapping combines small-scale mapping with large-scale analyses; thus, it is possible to reveal relations that are only visible from a wider perspective. While the northern mid-latitudes of Mars have already been analysed by using this method, there was no adequate equivalent for the southern hemisphere. We therefore mapped three study areas representative of the southern cratered highlands. These study areas were in Noachis Terra, Terra Cimmeria, and Terra Sirenum respectively. As the basement of the southern highlands has been formed during the Noachian, we considered all latitudes (from the equator to the pole) and climate-related landforms of all Martian eras (Amazonian, Hesperian, Noachian), in order to determine any possible morphoclimatic belts. Unlike on Earth, we could not simply transfer existing geomorphologic classes to Mars. Instead, we reclassified the landforms into H2O– and CO2-based morphologies, as both constituents have different physical properties. As a result, we detected three cumulative morphoclimatic environments, formed under the same or very similar conditions during the late Amazonian: an aeolian zone (0°-~30°S), an H2O zone (~30°-70°S), as well as a CO2 zone (≥70°S). The aeolian and H2O zones could be further subdivided into two subdivisions: an active (0°-10°S) and inactive (10°-~30°S) aeolian zone as well as a volatile/unstable (~30°S-~60°S) and permanent/stable (60°-~70°S) H2O zone. Our observations are consistent with recent models of the distribution of water-ice on the Martian surface during the Amazonian. Although we detected landforms pre-dating the Amazonian, we could not detect clear evidence for Noachian or Hesperian morphoclimatic environments, as more recent landforms cover most of the mid to high latitudes. Grid-mapping also enabled the finding of a widely undescribed crater morphology on Mars, which we term multi-annular craterlets. They are characterised by small diameters (<1 km), a multi-ring facies, and a widely flat topography (the former crater depression is entirely filled with multi-layered deposits). We suggest that they were formed during deposition and erosion of multiple layers of the latitude-dependent mantle

Hydroxyl airglow on Venus in comparison with Earth

International audienceHydroxyl nightglow is intensively studied in the Earth atmosphere, due to its coupling to the ozone cycle. Recently, it was detected for the first time also in the Venus atmosphere, thanks to the VIRTIS-Venus Express observations. The main Delta nu=1, 2 emissions in the infrared spectral range, centred, respectively, at 2.81 and 1.46 mum (which correspond to the (1-0) and (2-0) transitions, respectively), were observed in limb geometry ( Piccioni et al., 2008) with a mean emission rate of 880±90 and 100±40 kR (1R=10 6 photon cm -2 s -1 (4 pister) -1), respectively, integrated along the line of sight. In this investigation, the Bates-Nicolet chemical reaction is reported to be the most probable mechanism for OH production on Venus, as in the case of Earth, but HO 2 and O may still be not negligible as mechanism of production for OH, differently than Earth. The nightglow emission from OH provides a method to quantify O 3, HO 2, H and O, and to infer the mechanism of transport of the key species involved in the production. Very recently, an ozone layer was detected in the upper atmosphere of Venus by the SPICAV (Spectroscopy for Investigation of Characteristics of the Atmosphere of Venus) instrument onboard Venus Express ( Montmessin et al., 2009); this discovery enhances the importance of ozone to the OH production in the upper atmosphere of Venus through the Bates-Nicolet mechanism. On Venus, OH airglow is observed only in the night side and no evidence has been found whether a similar emission exists also in the day side. On Mars it is expected to exist both on the day and night sides of the planet, because of the presence of ozone, though OH airglow has not yet been detected. In this paper, we review and compare the OH nightglow on Venus and Earth. The case of Mars is also briefly discussed for the sake of completeness. Similarities from a chemical and a dynamical point of view are listed, though visible OH emissions on Earth and IR OH emissions on Venus are compared

Global Mapping of Venus' Atmosphere Using Accumulated Projections of Virtis Venus Express Observations

International audienc

Global Mapping of Venus' Atmosphere Using Accumulated Projections of Virtis Venus Express Observations

International audienc

Global Mapping of Venus' Atmosphere Using Accumulated Projections of Virtis Venus Express Observations

International audienc

The Mars Express limbs observations database

The capability to orient Mars Express allows a great diversity of observations modes, in particular nadir and limb. During day and night limb’s observations, 4 out of 7 MEX instruments (the spectrometers: SPICAM, OMEGA, PFS and the high-resolution camera HRSC) work together to provide spectra (.12 µ�m to 45 �µm) of the Martian atmosphere, at each altitude step, with the associated image. We will present the limbs database of more than 10 years in orbit with striking results (dust and clouds detached layers, day and night emissions). The database is now accessible to the scientific community via the ESA/PSA website (www.rssd.esa.int/PSA)

Calibration of Hyperspectral Imaging Data: VIRTIS-M Onboard Venus Express

International audienceThe Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) is flying onboard the European Space Agency mission Venus Express and orbiting around Venus since April 11, 2006, providing very valuable remote sensing data of the planet. The instrument combines a double capability: a high-resolution imaging in the visible-infrared range (0.28-5 um) at moderate spectral resolution (VIRTIS-M channel) and a high-resolution spectroscopy in the 2-5 um range (VIRTIS-H channel). The scientific objectives of VIRTIS cover a large field and span from the study of the thermal emission of the surface up to the composition and dynamics of the upper atmosphere. The team is composed of people coming from institutes from more than ten countries. About 2.5 Gb of raw compressed data is coming, in average, every day from the spacecraft, which is to be further processed and distributed to the team for data analysis. This paper is meant to be a reference for all of the calibration processes performed on the hyperspectral images of the VIRTIS-M channel, which will be useful for the analysis of the measurements, to improve the interpretation of the final products and ultimately to reach a better understanding of Venus' atmosphere