The Emirates Mars Mission (EMM) – Hope Probe – was developed to understand Mars atmospheric circulation, dynamics, and processes through characterization of the Mars atmosphere layers and its interconnections enabled by a unique high-altitude (19,970 km periapse and 42,650 km apoapse) low inclination orbit that will offer an unprecedented local and seasonal time coverage over most of the planet. EMM has three scientific objectives to (A) characterize the state of the Martian lower atmosphere on global scales and its geographic, diurnal and seasonal variability, (B) correlate rates of thermal and photochemical atmospheric escape with conditions in the collisional Martian atmosphere, and (C) characterize the spatial structure and variability of key constituents in the Martian exosphere. The EMM data products include a variety of spectral and imaging data from three scientific instruments measuring Mars at visible, ultraviolet, and infrared wavelengths and contemporaneously and globally sampled on both diurnal and seasonal timescale. Here, we describe our strategies for addressing each objective with these data in addition to the complementary science data, tools, and physical models that will facilitate our understanding. The results will also fill a unique role by providing diagnostics of the physical processes driving atmospheric structure and dynamics, the connections between the lower and upper atmospheres, and the influences of these on atmospheric escape.

We report a new water‐ice cloud feature observed during the Mars year 34 global dust storm: twilight cloud bands that routinely formed just past the evening terminator. We use images taken by the MAVEN/IUVS instrument. These bands were often latitudinally continuous, spanning over 6,000 km and were present between 18:00 and 19:00 local time. They were present for nearly the entire time IUVS imaged the evening terminator and often reached altitudes of at least 40 to 50 km during the mature phase of the storm. We compare these observations to LMD global climate model simulations. The simulations generally contain the temporal and spatial extents of the bands seen in IUVS data throughout the storm, but there are some discrepancies. We infer that these clouds formed as a result of semidiurnal thermal tides.

We model expected dynamo currents above, and resulting magnetic field profiles at, InSight's landing site on Mars, including for the first time the effect of electron-ion collisions. We calculate their diurnal and seasonal variability using inputs from global models of the Martian thermosphere, ionosphere, and magnetosphere. Modeled currents primarily depend on plasma densities and the strength of the neutral wind component perpendicular to the combined crustal and draped magnetic fields that thread the ionosphere. Negligible at night, currents are the strongest in the late morning and near solstices due to stronger winds and near perihelion due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the InSight landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind environment. Plain Language Summary In the upper atmospheres of planets, solar extreme ultraviolet (EUV) radiation produces ions and electrons. Electric currents flow whenever electrons and ions move differently from each other, due to their opposite charges and different masses. When neutral wind causes this differential motion, it is called a dynamo current. Here we simulate these dynamo currents above the NASA InSight Mars lander, resulting from magnetic and collision forces acting upon ions and electrons in the Martian upper atmosphere. We find that modeled currents primarily depend on (a) the density of electrons and ions and (b) the strength of the neutral wind component that is perpendicular to the combined draped and crustal magnetic field that sits within the Mars ionosphere. Negligible at night, predicted currents are the strongest in the late morning and near solstices, due to stronger winds, and near Mars' closest approach the sun, due to both stronger winds and higher plasma densities from solar EUV photoionization. Resulting surface magnetic fields of tens of nanotesla and occasionally >100 nT may be expected at the landing site. We expect currents and surface fields to vary significantly with changes in the draped magnetic field caused by Mars' dynamic solar wind and space weather environment.

Near-surface perennial water ice on Mars has been previously inferred down to latitudes of about 45° and could result from either water vapor diffusion through the regolith under current conditions or previous ice ages precipitations. In this paper we show that at latitudes as low as 25° in the southern hemisphere buried water ice in the shallow (< 1 m) subsurface is required to explain the observed surface distribution of seasonal CO2 frost on pole facing slopes. This result shows that possible remnants of the last ice age, as well as water that will be needed for the future exploration of Mars, are accessible significantly closer to the equator than previously thought, where mild conditions for both robotic and human exploration lie. While perennial water ice is routinely observed both at the surface and in the subsurface at high latitudes [Kieffer et al., 1976; Boyton, 2002; Mitrofanov, 2002; Bibring et al., 2004; Mellon et al., 2004; Bandfield and Feldman, 2008; Smith et al., 2009], only subsurface water ice can survive throughout the entire year at mid-latitudes. Evidence for shallow (< 1 m) subsurface water ice has been obtained from observations down to latitudes of about 45° in both hemispheres [Mellon et al., 2004; Byrne et al., 2009], and deeper buried glaciers have been locally inferred down to 40° latitude [Holt et al., 2008; Plaut et al., 2009]. It is not clear yet to what extent this subsurface ice has formed under current conditions via water vapor diffusion through the regolith and/or is the remnant of previous ice ages precipitations that occurred at higher obliquities [Mellon and Jalosky, 1995; Head et al., 2003; Schorghofer 2007; Hudson et al., 2009]. At more equatorward latitudes, morphological observations consistent with the past presence of shallow subsurface water ice have been reported [Squyres and Carr, 1986; Mustard et al., 2001; Head et al., 2003]. It has been suggested that this water ice may be locally preserved [Christensen, 2003], and modeling predictions indicate that subsurface water ice could be stable today on pole facing slopes at those latitudes [Aharonson and Schorghofer, 2006]. However, there is no observational evidence. The OMEGA (Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité onboard Mars Express) and CRISM (Compact Reconnaissance Imaging Spectrometer for Mars onboard Mars Reconnaissance Orbiter) near-infrared imaging spectrometers have been observing the surface of Mars since 2004 and 2006 respectively. These instruments measure solar radiation scattered by the surface, mainly in the first upper hundreds of microns. They provide spectral images with a spatial resolution ranging from 20 meters to 5 kilometers and a spectral sampling between 7 nm and 40 nm. While these data have been widely used to assess the composition of both minerals and condensates on the surface of Mars, they do not provide direct evidence of the properties of the subsurface. Nevertheless, surface conditions are partly driven by the thermal properties of the subsurface. In fact, the current amount of CO2 that

The SPICAM experiment onboard Mars Express has accumulated during the last decade a wealth of observations that has permitted a detailed characterization of the atmospheric composition and activity from the near-surface up to above the exosphere. The SPICAM climatology is one of the longest assembled to date by an instrument in orbit around Mars, offering the opportunity to study the fate of major volatile species in the Martian atmosphere over a multi-(Mars)year timeframe. With his dual ultraviolet (UV)-near Infrared channels, SPICAM observes spectral ranges encompassing signatures created by a variety atmospheric gases, from major (CO2) to trace species (H2O, O-3). Here, we present a synthesis of the observations collected for water vapor, ozone, clouds and dust, carbon dioxide, exospheric hydrogen and airglows. The assembled climatology covers the MY 27-MY 31 period. However, the monitoring of UV-derived species was interrupted at the end of 2014 (MY30) due to failure of the UV channel. A SO2 detection attempt was undertaken, but proved unsuccessful from regional to global scales (with upper limit greater than already published ones). One particular conclusion that stands out from this overview work concerns the way the Martian atmosphere organizes an efficient mass transfer between the lower and the upper atmospheric reservoirs. This highway to space, as we name it, is best illustrated by water and hydrogen, both species having been monitored by SPICAM in their respective atmospheric reservoir. Coupling between the two appear to occur on seasonal timescales, much shorter than theoretical predictions. (C) 2017 The Authors. Published by Elsevier Inc.

We present here the comparison of the electron den- sity profiles predicted by a 3D global climate model (GCM), the Mars GCM developed at the Laboratoire de Meteorologie Dynamique (LMD-MGCM) [4], with the measurements from the instrument MARSIS on board Mars Express [5]. The observations were ob- tained during 5 Martian Years (MY), from MY27 to MY31 (mid 2005-end of 2013). The model was run using the observed day-to-day variability of the UV solar flux and of the dust load during that period. We focus the comparison on two parameters: the electron density at the main peak, and the altitude of the peak. Special attention will be paid to the variability of these two parameters with different geophysical parameters (latitude, SZA, ...), which can provide interesting in- formation about the neutral upper atmosphere of Mars and its interaction with the UV solar radiation.

A dedicated mission to investigate exoplanetary atmospheres represents a major milestone in our quest to understand our place in the universe by placing our Solar System in context and by addressing the suitability of planets for the presence of life. EChO -the Exoplanet Characterisation Observatory- is a mission concept specifically geared for this purpose. EChO will provide simultaneous, multi-wavelength spectroscopic observations on a stable platform that will allow very long exposures. EChO will build on observations by Hubble, Spitzer and groundbased telescopes, which discovered the first molecules and atoms in exoplanetary atmospheres. EChO will simultaneously observe a broad enough spectral region -from the visible to the mid-IR- to constrain from one single spectrum the temperature structure of the atmosphere and the abundances of the major molecular species. The spectral range and resolution are tailored to separate bands belonging to up to 30 molecules to retrieve the composition and temperature structure of planetary atmospheres. The target list for EChO includes planets ranging from Jupiter-sized with equilibrium temperatures Teq up to 2000 K, to those of a few Earth masses, with Teq 300 K. We have baselined a dispersive spectrograph design covering continuously the 0.4-16 micron spectral range in 6 channels (1 in the VIS, 5 in the IR), which allows the spectral resolution to be adapted from several tens to several hundreds, depending on the target brightness. The instrument will be mounted behind a 1.5 m class telescope, passively cooled to 50 K, with the instrument structure and optics passively cooled to 45 K. EChO will be placed in a grand halo orbit around L2. We have also undertaken a first-order cost and development plan analysis and find that EChO is easily compatible with the ESA M-class mission framework.

Martian gully landforms resemble terrestrial debris flows formed by the action of liquid water and have thus been interpreted as evidence for potential habitable environments on Mars within the past few millennia. However, ongoing gully formation has been detected under surface conditions much too cold for liquid water, but at times in the martian year when a thin layer of seasonal CO 2 frost is present and defrosting above the regolith. These observations suggest that the CO 2 condensation–sublimation cycle could play a role in gully formation. Here we use a thermo-physical numerical model of the martian regolith underlying a CO 2 ice layer and atmosphere to show that the pores beneath the ice layer can be filled with CO 2 ice and subjected to extreme pressure variations during the defrosting season. The subsequent gas fluxes can destabilize the regolith material and induce gas-lubricated debris flows with geomorphic characteristics similar to martian gullies. Moreover, we find that subsurface CO 2 ice condensation, sublimation and pressurization occurs at conditions found at latitudes and slope orientations where gullies are observed. We conclude that martian gullies can result from geologic dry ice processes that have no terrestrial analogues and do not require liquid water. Such dry ice processes may have helped shape the evolution of landforms elsewhere on the martian surface.

We present for the first time an assimilation of Thermal Emission Spectrometer (TES) water vapour column data into a Mars global climate model (MGCM). We discuss the seasonal cycle of water vapour, the processes responsible for the observed water vapour distribution, and the cross-hemispheric water transport. The assimilation scheme is shown to be robust in producing consistent reanalyses, and the global water vapour column error is reduced to around 2-4 pr mu m depending on season. Wave activity is shown to play an important role in the water vapour distribution, with topographically steered flows around the Hellas and Argyre basins acting to increase transport in these regions in all seasons. At high northern latitudes, zonal wavenumber 1 and 2 stationary waves during northern summer are responsible for spreading the sublimed water vapour away from the pole. Transport by the zonal wavenumber 2 waves occurs primarily to the west of Tharsis and Arabia Terra and, combined with the effects of western boundary currents, this leads to peak water vapour column abundances here as observed by numerous spacecraft. A net transport of water to the northern hemisphere over the course of one Mars year is calculated, primarily because of the large northwards flux of water vapour which occurs during the local dust storm around Ls = 240-260 degrees. Finally, outlying frost deposits that surround the north polar cap are shown to be important in creating the peak water vapour column abundances observed during northern summer. (C) 2014 Elsevier Inc. All rights reserved.

We examine the Martian valley networks in the framework of topographic influences on precipitation. We use an analytical model and the Laboratoire de Météorologie Dynamique (LMD) early Mars global circulation model (GCM) to explore the local‐scale distribution of orographically forced precipitation as a function of atmospheric pressure. In simulations with 500 mbar and 1 bar CO2 atmospheres, orographic lifting results in enhanced snowfall upslope of the observed valley network tributaries. Our framework also suggests that a 2 bar atmosphere cannot create the observed valley pattern at the highest‐relief valley network, Warrego Valles. As in previous work, the GCM does not generate temperatures warm enough for rain or significant snowmelt in the highlands with CO2 greenhouse warming alone. Thus while transient periods of unusual warming are still required to melt the deposits and carve the valleys, our model predicts snow deposition in the correct locations.

The inner edge of the classical habitable zone is often defined by the critical flux needed to trigger the runaway greenhouse instability. This 1D notion of a critical flux, however, may not be so relevant for inhomogeneously irradiated planets, or when the water content is limited (land planets). Here, based on results from our 3D global climate model, we find that the circulation pattern can shift from super-rotation to stellar/anti stellar circulation when the equatorial Rossby deformation radius significantly exceeds the planetary radius. Using analytical and numerical arguments, we also demonstrate the presence of systematic biases between mean surface temperatures or temperature profiles predicted from either 1D or 3D simulations. Including a complete modeling of the water cycle, we further demonstrate that for land planets closer than the inner edge of the classical habitable zone, two stable climate regimes can exist. One is the classical runaway state, and the other is a collapsed state where water is captured in permanent cold traps. We identify this "moist" bistability as the result of a competition between the greenhouse effect of water vapor and its condensation. We also present synthetic spectra showing the observable signature of these two states. Taking the example of two prototype planets in this regime, namely Gl581c and HD85512b, we argue that they could accumulate a significant amount of water ice at their surface. If such a thick ice cap is present, gravity driven ice flows and geothermal flux should come into play to produce long-lived liquid water at the edge and/or bottom of the ice cap. Consequently, the habitability of planets at smaller orbital distance than the inner edge of the classical habitable zone cannot be ruled out. Transiting planets in this regime represent promising targets for upcoming observatories like EChO and JWST.

T. Appere, B. Schmitt, Institut de Planetologie et d'Astrophysique de Grenoble, Universite J. Fourier, CNRS/INSU, Grenoble, France (thomas.appere@obs.ujf-grenoble.fr), Y. Langevin, Institut d'Astrophysique Spatiale, Universite Paris-Sud XI, CNRS/INSU, Orsay, France, A. Spiga, Laboratoire de Meteorologie Dynamique, IPSL, CNRS/INSU, Universite Pierre et Marie Curie, Paris, France, S. Doute, A. Pommerol, Physikalisches Institut, Universitat Bern, Silderstrasse 5, CH-3012 Bern, Schwitzerland, F. Forget, B. Gondet and J.-P. Bibring

This article reflects my personal experience and illustrates some developments in the field of planetary spectroscopy, achieved within the Planetology Group of Paris Observatory over the past fifty years. Over these decades, planetary spectroscopy has led to the identification of minor atmospheric species with mixing ratios as low as a few parts per billion (ppbv). Since the early 1970s, we have been measuring infrared spectra of giant planets and their satellites, in order to search for new minor species and to determine elemental and isotopic ratios, for better constraining their formation and evolution processes. In particular, observations of Jupiter at the time of the Shoemaker-Levy 9 collision, in 1994, allowed us to monitor the thermal sequence and the formation of stratospheric water vapor; a few years later, spectra taken by the Infrared Space Observatory confirmed the presence of an external oxygen source in all giant planets and Titan. More recently, the advent of bi-dimensional infrared arrays has allowed us to map the distribution of these components over planetary disks, and to use them as tracers of dynamical and photochemical processes. In complement to in-orbit observations recorded by space missions, high-resolution spectral mapping from the ground allows us to obtain instantaneous global maps of the planets, and thus to trace transient phenomena or temporal variations of minor atmospheric species over short and long timescales. Over the past twenty years, we have been monitoring the behavior of minor atmospheric species on Mars and Venus, using the TEXES (Texas Echelon Cross Echelle Spectrograph) at the NASA IRTF (InfraRed Telescope Facility) at Maunakea Observatory, and the EXES (Echelon Cross Echelle Spectrograph) aboard SOFIA (Stratospheric Observatory For Infrared Astronomy): H2O2 and H2O on Mars, D/H on Mars, SO2 and H2O at the cloud top of Venus. In addition, in an attempt to build a 3-D image of the sulfur and water cycles on Venus, we have obtained maps of SO, SO2 and HDO in its upper mesosphere (about 20 km above the cloud top) using the ALMA (Atacama Large Millimeter/submillimeter Array) facility in Chile. These observations are presented and discussed in the light of global dynamical and photochemical models, and interpreted in the context of the past and present history of these planets. In the conclusion, I present the perspectives of this work for the forthcoming development of exoplanetary spectroscopy.

We will summarize 3.5 Martian years (Mars Years 27-30) of high-altitude CO2 cloud data from MEx/OMEGA and selected results from Mex/HRSC. The 3-year dataset shows that the equatorial cloud activity is centered around the northern summer solstice with a pause at the aphelion, and that their appearance is limited in latitude and longitude. HRSC-measured altitudes and cloud speeds provide a rare dataset for comparison with GCMs. A comparison with the LMD Mars Global Climate Model shows a good agreement between the model-predicted winds and those observed by the HRSC. The LMD-MGCM predicts a strong diurnal variation of temperature at the cloud observation altitudes due to the propagation of the diurnal thermal tide. The coldest temperatures in the near-equator cloud altitude range (60-85 km) are observed towards the end of the afternoon, whereas the warmest temperatures are found in the early morning hours. Most of the observed clouds are cirrus-type, filamented clouds, but some OMEGA-observed clouds exhibit round, clumpy structures that have been suggested to be of convective origin. We asses the plausibility of the hypothesis of mesospheric convection in light of observations and theoretical Convective Available Potential Energy calculations. Estimates of convective potential and vertical velocities based on observed cloud properties suggest that the convective clouds could most likely be clusters of smaller scale convective updrafts. SPICAM stellar occultations have revealed large supersaturations at high altitudes: to attain the estimated values of CAPE and vertical velocity, most probably only moderate deviations from saturation are required. Based on nucleation modeling, such deviations may imply cloud formation via heterogeneous nucleation onto small condensation nuclei.