Search

Selected in 2021 as the fifth class M mission of ESA’s “Cosmic Vision” programme, EnVision is one the three next exploration mission of Venus, alongside NASA’s VERITAS and DAVINCI. EnVision will bring a holistic approach, by studying the surface and subsurface, different layers of the atmosphere, past and present volcanic activity, as well as coupling processes. To that end, the payload will include a synthetic aperture radar for surface mapping (VenSAR, NASA), a subsurface radar sounder and a radioscience experiment to monitor gravimetric and atmospheric properties.Finally, the spectrometer suite VenSpec will investigate the surface and atmospheric compositions to analyse their relations with internal activity, using the thermal IR imager VenSpec-M and the high-resolution IR spectrometer VenSpec-H. The UV channel of the suite VenSpec-U, also called VeSUV, will focus on the atmosphere above the clouds, and aims more specifically at characterising the abundance and variability of sulphured gases such as SO and SO2, and the unidentified UV absorber. To do so, VeSUV will operate in pushbroom mode in the 190-380 nm range with an improved spectral resolution between 205 and 235 nm, and will observe the backscattered sunlight on the dayside of Venus at a spatial sampling ranging from 3 to 24 km.In order to characterise the instrument’s performances, the sensitivity to bias is analysed using a gain matrix formulation. A perturbation is locally introduced on a synthetic spectrum and a fitting algorithm involving the same radiative transfer model is used to retrieve the atmospheric parameters, for several values of perturbation. As they are small, the assumption of a linear relation between the perturbation and the resulting error on the estimated parameters is made, their ratio corresponding to the matrix element. This method allows a conversion between the measured signal and the atmospheric parameters independently from the bias spectrum (e.g. straylight, calibration error, contamination during mission), as it is computed separately for each wavelength.

EnVision was selected as ESA’s 5th M-class mission, targeting a launch in the early 2030s. The mission is a partnership between ESA and NASA, where NASA provides the Synthetic Aperture Radar payload. The scientific objective of EnVision is to provide a holistic view of the planet from its inner core to its upper atmosphere. The mission phase B1 started in December 2021 to complete trade-offs, consolidate requirements, interfaces and system specifications. Phase B1 will be concluded with the Mission Adoption Review planned in fall 2023, followed by Mission Adoption in 2024. To meet its science objectives, the EnVision mission needs to return a significant volume of science data to Earth, with a large distance-to-Earth dynamic range (from 0.3 to 1.7 AU), from a low Venus polar orbit, in the hot Venus environment (exacerbated by the operation of highly dissipative units), while operating three spectrometers in an almost cryogenic level environment. This needs to be achieved within constraints on the spacecraft mass as well as Agency programmatic boundaries. Achieving the science objectives under these multiple constraints without oversizing the spacecraft calls for a careful planning of science operations, making the science planning strategy a critical driver in the design of the whole mission, against which the spacecraft and ground segment are then sized.The payload reference operations scenario simulation demonstrates that all identified surface targets can be imaged with VenSAR, with a performance fully compliant with the science requirements. The first two cycles allow imaging once 80% of the identified Regions of Interest (RoIs) at 30 m resolution. The following two cycles are mostly devoted to 2nd observations of these areas for stereo-topography mapping and the two last cycles to 3rd observations of the “activity” type. Dual polarization and high resolution SAR observations can be performed at any longitude at least once across the 6 cycles. Our strategy is to obtain the widest range of data types that enables us to put the highest resolution datasets into regional and global context. Similarly, understanding atmospheric processes requires a combination of global-scale mapping with targeted observations resolving smaller-scale processes.

The VenSpec-H instrument is part of the EnVision payload. EnVision is a medium class mission to determine the nature and current state of geological activity on Venus, and its relationship with the atmosphere, to understand how Venus and Earth could have evolved so differently. The launch of the spacecraft is planned in 2031 for a 4 years mission duration. VenSpec-H is part of the VenSpec suite [1], including also an IR mapper and a UV spectrometer [2] suite. The science objectives of this suite are to search for temporal variations in surface temperatures and tropospheric concentrations of volcanically emitted gases, indicative of volcanic eruptions; and study surface-atmosphere interactions and weathering by mapping surface emissivity and tropospheric gas abundances. Recent and perhaps ongoing volcanic activity has been inferred in data from both Venus Express and Magellan. Maintenance of the clouds requires a constant input of H2O and SO2. A large eruption would locally alter the composition by increasing abundances of H2O, SO2 and CO and perhaps decreasing D/H ratio. Observations of changes in lower atmospheric SO2, CO and H2O vapour levels, cloud level H2SO4 droplet concentration, and mesospheric SO2, are therefore required to link specific volcanic events with past and ongoing observations of the variable and dynamic mesosphere, to understand both the importance of volatiles in volcanic activity on Venus and their effect on cloud maintenance and dynamics. To contribute to this investigation, VenSpec-H is designed to measure H2O, HDO, CO, OCS and SO2 both on the nightside and on the dayside. To ensure the reliability of the analysis, the BIRA-IASB radiative transfer code, ASIMUT-ALVL [3], has been scrutinized making sure all contributions were properly modelled. The radiances of the nightside atmosphere of Venus originate from the thermal emission of the surface and atmosphere while on the dayside they originate from the sunlight penetrating the atmosphere and bouncing back on the cloud cover. While VenSpec-H will be able to measure 4 spectral ranges between 1 to 2.5 microns, we focused on the upper wavelengths’ range, from 2.35 to 2.5 microns, identified as Band#2 in VenSpec-H’s design and enabling simultaneous measurements of the different molecular species. A sensitivity study was performed on nightside spectra. The impacts of the molecular species (line by line and collision induced absorption) and of the aerosols were quantified. We will discuss the choices we have made in terms of absorption line parameters and clouds’ physical properties Acknowledgements This work has been performed with the support of the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office. References [1] J. Helbert et al., “The VenSpec suite on the ESA EnVision mission to Venus”, Proc. SPIE 11128, Infrared Remote Sensing and Instrumentation XXVII, 1112804 (2019). [2] E. Marcq et al., “Instrumental requirements for the study of Venus’ cloud top using the UV imaging spectrometer VeSUV”, Advances in Space Research, 68 (2021) 275-291. [3] A.C. Vandaele, M. Kruglanski and M. De Mazière, “Modeling and retrieval of atmospheric spectra using ASIMUT”, Proc. of the First 'Atmospheric Science Conference', ESRIN, Frascati, Italy, 2006.

EnVision was selected as ESA's 5th Medium-class mission in the Agency's Cosmic Vision plan, targeting a launch in the early 2030s. EnVision's overarching science questions are to explore the full range of geoscientific processes operating on Venus. It will investigate Venus from its inner core to its atmosphere at an unprecedented scale of resolution, characterising in particular core and mantle structure, signs of past geologic processes, and looking for evidence of past liquid water. Far more than a simple radar mission, this suite of investigations works together to comprehensively assess surface and subsurface geological processes, interior geophysics and geodynamics, and atmospheric pathways of key volcanogenic gases, which together illuminate how and why Venus turned out so differently to Earth. Recent modeling studies strongly suggest that the evolution of the atmosphere and interior of Venus are coupled, emphasizing the need to study the atmosphere, surface, and interior of Venus as a system. EnVision is an ESA Venus orbiter mission formulated in collaboration with NASA; As a key partner in the mission, NASA provides the Synthetic Aperture Radar, VenSAR. The EnVision payload consists of five instruments provided by European and US institutions. The five instruments comprise a comprehensive measurement suite spanning infrared, ultraviolet- visible, microwave and high frequency wavelengths, complemented by the Radio Science investigation exploiting the spacecraft TT&C system. All instruments in the payload have substantial heritage and robust margins relative to the requirements with designs suitable for operation in the Venus environment. This suite of instruments was chosen to meet the broad spectrum of measurement requirements needed to support EnVision science investigations.

Introduction The VenSpec-H instrument is part of the EnVision M5 mission payload, which has been selected by ESA in June 2021 for launch in 2031. EnVision is a medium-class mission to determine the nature and current state of geological activity on Venus, and its relationship with the atmosphere, to understand how Venus and Earth could have evolved so differently. VenSpec-H will target different molecular species in nadir viewing geometry, as to better characterize the surface-atmosphere interaction. VenSpec-H is part of the VenSpec suite [1], including also an IR mapper and a UV spectrometer [2]. Instrument VenSpec-H is a nadir pointing, high-resolution (R~8000) infrared spectrometer that will perform observations in different spectral windows between 1 and 2.5 microns. This instrument was originally developed with direct heritage from NOMAD-LNO [3, 4] that is currently onboard ExoMars Trace Gas Orbiter. Due to the scientific requirements of the EnVision mission, a series of modifications have been introduced to address the spectral coverage and SNR of the instrument. A significant effort is now undergoing to develop and validate these “new” components for the operational environments and mission lifetime. The VenSpec-H instrument is comprised of two boxes as shown above, the instrument box and the electronics box. The instrument box contains a warm base plate (0°C operating temperature) where the filter wheel and detector/cooler are mounted, and a cold base plate (-45°C operating temperature) where the majority of the optical elements are mounted. The majority of the electronics are in a separate box to improve the thermal stability of the instrument box. Consortium The VenSpec-H consortium is led by Belgium with the participation of Spain, Netherlands, Switzerland, Germany, Portugal, and Czech Republic. The organization is outlined below. With such a large consortium, communication and organization are essential. To this effect we hold regular full team meetings, as well as smaller focus groups on topics such as filter wheel, thermal/mechanical, optical development, and polarization. Acknowledgements This work has been performed with the support of the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office. References [1] Helbert, J., et al., Proc. SPIE 11128, Infrared Remote Sensing and Instrumentation XXVII, 1112804 (2019) [2] Marcq et al., “Instrumental requirements for the study of Venus’ cloud top using the UV imaging spectrometer VeSUV”, Advances in Space Research, 68 (2021) 275-291. [3] Neefs, E., et al., Appl Opt 54(28), 8494-520 (2015) [4] Vandaele, A.C., et al., Space Science Reviews 214(5) (2018)

Large planetesimals and planetary embryos ranging from several hundred to a few thousand kilometers can develop magma oceans through mutual collisions, gravitational energy, and the heating of short-lived radioactive elements. After the evaporation of the protoplanetary gas disk, one can divide such planetary embryos into two distinct populations. If they grow to a certain mass of about >0.5 MEarth before the dissipation of the disk, they will start to accrete a substantial primordial hydrogen-dominated atmosphere, while the gravitational potential of the smaller ones (≤0.5 MEarth) will be too low to support this type of primordial atmosphere. For the smaller planetary embryos, the initial magma ocean will subsequently solidify, and a steam atmosphere will be catastrophically outgassed that, if it does not condense, may be lost efficiently via hydrodynamic escape. The escaping H-atoms will further drag heavier trace elements like noble gases and outgassed moderately volatile elements (MVEs) such as K, Na, Si, and Mg into space. For the larger population of planetary embryos, however, the magma ocean below the primordial atmosphere will not solidify until most of the gaseous envelope will be lost, thereby providing favorable conditions for MVEs to be dissolved within such atmosphere. In our first study (Benedikt et al. 2020), we applied an upper atmosphere hydrodynamic escape model that includes the dragging of heavier species by escaping H-atoms and investigated atmospheric and elemental escape from planetary embryos between 1 MMoon and 1.5 MMars (that is, the population of small protoplanets that does not accrete a primordial hydrogen-dominated atmosphere) by assuming that the noble gases and MVEs mostly reside within the escaping atmosphere. Our results indicated that the steam atmospheres and the embedded trace elements will be lost efficiently before they condense for masses ≤0.5 MMars and orbital distances up to 1 AU. For heavier embryos of up to 1.5 MMars the atmosphere together with the trace elements can only be lost completely if a shallow magma ocean remains below the gaseous envelope which might be achieved through frequent impacts onto the planetary embryo. For embryos with masses ≤MMoon, on the other hand, the gravity is too weak for a dense atmosphere to build up against the high magma ocean related surface temperatures and all outgassed elements will escape immediately into space. The studied planetary embryos will, therefore, be severely depleted in noble gases and MVEs. In a follow-up study (Erkaev et al. 2022), we are currently focusing on the loss of the heat producing element 40K from initially bigger planetary embryos (that is, the population of protoplanets that was able to accrete a substantial primordial atmosphere). Contrary to our first study, we additionally applied equilibrium condensation models with the equilibrium chemistry GGCHEM code (Woitke et al. 2018) and found that for magma ocean surface temperatures of ≥2500 K no condensates that fix potassium are thermally stable, and 40K isotopes indeed populate such a primordial atmosphere to a great extent. By applying a sophisticated multispecies hydrodynamic upper atmosphere evolution model to study the loss of the atmosphere together with 40K, we found that depending on the initial size of the protoplanet and the early evolution of the host star, this process can indeed remove substantial amounts of 40K from protoplanetary bodies that are ≥0.5 MEarth. This effect alone can, together with the loss of MVEs from the smaller planetary embryos that serve as building blocks for the bigger ones, result in a wide variety of different potassium abundances at the fully grown planet. Since different abundances of heat producing elements have a significant influence onto the subsequent thermal and tectonic evolution of a planet, and therewith connected, on its tectonic modes (e.g., O’Neill et al. 2020), the process of early hydrodynamic escape of the heat producing isotope 40K can significantly impact the habitability, since not all rocky planets will end up with the "right" amount of heat production in its interior. However, this process cannot be viewed separately; other factors will additionally determine the initial heat budget of a planet such as collisional erosion, the feeding zone of the growing protoplanet or the initial composition of the protoplanetary disk. References: Benedikt, M.R., Scherf, M., Lammer, H., Marcq, E., Odert, P., Leitzinger, M., Erkev, N.V., Escape of rock-forming volatile elements and noble gases from planetary embryos, Icarus, 347, 113772, 2020.Erkaev, N.V., Scherf, M., Herbort, O., Lammer, H., Odert, P., Kubyshkina, D., Leitzinger, M., Woitke, P., O’Neill, C., Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres, Mon. Not. R. Ast. Soc., under revision, 2022.O’Neill, C., O’Neill, H.S.C., Jellinek, A.M., On the Distribution and Variation of Radioactive Heat Producing Elements Within Meteorites, the Earth, and Planets, Space Sci. Rev., 216, id.37, 2020.Woitke, P., C. Helling, Hunter, G.H., Millard, J.D., Turner, G.E., Worters, M., Blecic, J., Stock, J.W., Equilibrium chemistry down to 100 K. Impact of silicates and phyllosilicates on the carbon to oxygen ratio, Astron. Astrophys. 614, id.A1, 2018.

Water-rich planets should be ubiquitous in the universe, and could represent a notable fraction of the sub-Neptune population. Among the detected exoplanets that have been characterized as sub-Neptunes, many are subject to important irradiation from their host star. As a consequence, hydrospheres of such planets are not in condensed phase, but are rather in supercritical state, with steam atmospheres on top. Such irradiated ocean planets (IOP) are good candidates to explain the distribution of masses and radii in the sub-Neptune category of exoplanets [1]. Here, we present the IOP model that computes the structure of water-rich planets that have high irradiation temperatures. The IOP model [2] combines two models in a self-consistent way: one for the interior structure, and one for the steam atmosphere. The interior structure model [3] contains several refractory layers (iron core and rocky mantle), and on top of them an hydrosphere with an up to date equation of state (EOS) with a validity range that extends to the plasma regime. The atmosphere model [4] connects the top of the interior model with the host star by solving equations of radiative transfer. Our model has been applied to the GJ 9827 system as a test case and indicates Earth- and Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction of ∼20 ± 10%. We also compute mass-radius relationships for IOP and their analytical expression, which can be found in [2]. This allows one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. Due to their high irradiation temperatures, sub-Neptunes are expected to be subject to strong atmospheric escape. This supports the idea that a massive hydrosphere could be the remnant of a complete loss of an H-He envelope. The stability of hydrospheres themselves is discussed as well [5]. Figure 1. Mass-radius relationships produced by our model (green, yellow and red thick lines) [2], compared to mass-radius relationships of planets with only condensed phases and no atmosphere (black, grey and light blue thin lines). A few planets of the solar system, the GJ-9827 system and the TOI-178 system are represented as well. Shaded regions correspond to important atmospheric loss by Jeans escape (H and H2O), or hydrodynamic escape. [1] Mousis, O., Deleuil, M., Aguichine, A., et al. 2020, ApJL, 896, L22.[2] Aguichine, A., Mousis, O., Deleuil, M., et al. 2021, ApJ, 914, 84A.[3] Brugger, B., Mousis, O., Deleuil, M., et al. 2017, ApJ, 850, 93.[4] Marcq, E., Baggio, L., Lefèvre, F., et al. 2019, Icarus, 319, 491M.[5] Vivien, H., Aguichine, A., Mousis, O., et al. 2022, accepted in ApJ.

From 2006 to 2014, the ESA Venus Express orbiter has provided a wealth of data that has not been fully analyzed yet. Here, using all available and suitable night side thermal spectra provided by the -H channel of the VIRTIS spectral imaging suite near 2.3 µm, we constrained the vertical profiles of various trace gases (CO, OCS, H2O or HDO, SO2) below the clouds in the 30-40 km altitude range. With the help of an updated version of the radiative transfer model used in our first study [Marcq et al., 2008], our preliminary results confirm previously reported findings [Marcq et al., 2008; Tsang et al., 2009; Arney et al., 2014], especially the latitudinal anti-correlation of CO and OCS. Such reanalyses of past data sets are relevant more than ever, since they provide background truth for designing future instruments on board recently selected missions towards Venus, such as the high-resolution IR spectrometer VenSpec-H onboard ESA's EnVision. Figure 1 (left): Best CO and cloud opacity fit of a VIRTIS-H (order 6) spectrum acquired during orbit #277Figure 2 (right) : Retrieved CO abundances (with 1σ error bars) near 36 km with respect to latitude.

On June 10, 2021, the European Space Agency (ESA) announced the selection of EnVision as its newest medium-class science mission. EnVision's overarching science questions are to explore the full range of geoscientific processes operating on Venus [1, 2]. It will investigate Venus from its inner core to its atmosphere at an unprecedented scale of resolution, characterising in particular core and mantle structure, signs of past geologic processes, and looking for evidence of past liquid water. Recent modeling studies strongly suggest that the evolution of the atmosphere and interior of Venus are coupled, emphasizing the need to study the atmosphere, surface, and interior of Venus as a system. The nominal science phase of the mission will last six Venus sidereal days (four Earth years). EnVision will downlink 210 Tbits of science data, using a Ka-/X-band comms system with a 2.5 m diameter fixed high-gain antenna. As a key partner in the mission, NASA provides the Synthetic Aperture Radar, VenSAR.The EnVision payload consists of five instruments provided by European and US institutions. The five instruments comprise a comprehensive measurement suite spanning infrared, ultraviolet-visible, microwave and high frequency wavelengths. This suite is complemented by the Radio Science investigation exploiting the spacecraft TT&C system. All instruments in the payload have substantial heritage and robust margins relative to the requirements with designs suitable for operation in the Venus environment. This suite of instruments was chosen to meet the broad spectrum of measurement requirements needed to support EnVision science investigations. Two parallel competitive industrial studies will continue in the Definition Phase B1, to complete trade-offs, consolidate requirements and interfaces, produce system specifications, support development of the science operations, calibration strategies, science products definition under the responsibility of the Future Missions Department (SCI-F) and under the authority of the EnVision Study Manager until Mission Adoption Review (MAR) scheduled in 2024. [1] ESA's EnVision Assessment Study Report: sci.esa.int/web/cosmic-vision/envision-assessment-study-report-yellow-book. [2] EnVision mission website: www.envisionvenus.eu.

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution., Comment: Ariel Definition Study Report, 147 pages. Reviewed by ESA Science Advisory Structure in November 2020. Original document available at: https://www.cosmos.esa.int/documents/1783156/3267291/Ariel_RedBook_Nov2020.pdf/

International audience; While the Ariel mission is primarily designed for the study of warm and hot objects, with an equilibrium temperature above 500 K, in this paper we want to explore a larger sample of possible colder targets. We thus investigate the detectability with Ariel of “temperate” exoplanets (with an equilibrium temperature of 400 K). We first consider the case of hydrogen-rich exoplanets (from Jupiters to sub-Neptunes) and we calculate their infrared transmission spectrum for several classes of stars. We consider the Tier 2 mode of Ariel, for which the resolving power (R = 50 for l < 4 mm and R=15 for l > 4 mm) is sufficient to get information about the chemical composition of the objects. Results show that temperate Jupiters and sub-Neptunes around all types of stars from G2 to M8, with revolution periods of a few tens of days and transit durations of a few hours, could be observed with Ariel, up to distances of about 50 pc for Jupiters and 25 pc for sub-Neptunes. In the case of temperate super-Earths, we estimate that they will not be observable in the Ariel Tier 2 mode. In a study of currently available target candidates, we find one sub-Neptune (TOI-178 g) as possibly observable in Ariel’s Tier 2. This study, a follow-up of “Transit spectroscopy of temperate Jupiters with ARIEL: A feasibility study” (Encrenaz et al., Exp. Astr. 46:31-44, 2018), is submitted to the ARIEL special issue of Experimental Astronomy (manuscript under revision)

Water-rich planets should be ubiquitous in the universe. Among the current exoplanet populations, many of those worlds are subject to important irradiation from their host star. As a consequence, water-rich worlds display supercritical water layer surrounded by an extended steam atmosphere making them good candidates for matching the observed mass-radius distribution of sub-Neptunes [1]. Here we describe a model that computes a realistic structure for water-rich planets by combining an interior model with an updated equation of state (EoS) for water, and an atmospheric model that takes into account radiative transfer. Our model has been applied to the GJ 9827 system as a test case and indicates Earth- or Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction of ∼20 ± 10%. We also provide mass-radius relationships for water-rich planets and their analytical expression. This allows one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. The possible existence of such planets is discussed in light of atmospheric loss processes, suggesting that some sub-Neptunes are the outcome of planets that lost their H/He reservoirs. Figure 1. Mass-radius relationships produced by our model (green, yellow and red thick lines) [2], compared to mass-radius relationships of planets with only condensed phases and no atmosphere (black, grey and light blue thin lines) [3,4]. A few planets of the solar system, the GJ-9827 system and the TOI-178 system are shown as well [5,6]. [1] Mousis, O., Deleuil, M., Aguichine, A., et al. 2020, ApJL, 896, L22.[2] Aguichine, A., Mousis, O., Deleuil, M., et al. 2021, accepted in ApJ.[3] Zeng, L., Sasselov, D. D., & Jacobsen, S. B. 2016, ApJ, 819, 127.[4] Brugger, B., Mousis, O., Deleuil, M., et al. 2017, ApJ, 850, 93.[5] Kosiarek, M. R., Berardo, D. A., Crossfield, I. J. M., et al. 2021, AJ, 161, 47.[6] Leleu, A., Alibert, Y., Hara, N. C., et al. 2021, A&A, 649, A26.

Exoplanets with size between the Earth and Neptune (1-4R⊕) do not have any equivalent in our Solar System and remain challenging to characterize. Yet, there are ubiquitous in the Galaxy and Fulton et al. (2017) showed that their distribution (number of planets per star vs radius) is bimodal highlighting a gap in the number of planets around 1.7R⊕. Planets with a radius below 1.7R⊕ are thought to be mostly rocky planets, and called Super-Earth, above this limit planets are most likely made of gas and called Sub-Neptune. We made use of the available data from the Hubble Space Telescope in Near-Infrared (HST WFC3 G141) and gathered 18 transmission spectra of planets with size below 6 R⊕ to study the transition between rocky and gaseous planets. First, we used TauREx3 (Al-Refaie et al. 2019), a Bayesian retrieval code, to rule out atmospheric scenarios. We proved that a primary clear atmosphere dominated by Hydrogen and Helium is rejected with more than 3σ for a large majority of planets in the sample. Then, we measured the amplitude of the spectra in the water absorption band (around 1.4μm) and compared observational values to simulated ones using a self-consistent modeling code ExoREM (Baudino et al. 2015; Charnay et al. 2018). We explored the connection between the water absorption amplitudes and the temperature by setting the stellar and planetary parameters to those of HD 3167 c (2.7 R⊕, 8.33 M⊕) and trying different metallicities (1, 10, 100 and 1000 x solar), cloud compositions and temperatures (300-1200K).

The VenSpec-H instrument is part of the EnVision payload which is currently being evaluated by ESA for mission selection. EnVision is a medium class mission to determine the nature and current state of geological activity on Venus, and its relationship with the atmosphere, to understand how Venus and Earth could have evolved so differently. VenSpec-H is part of the VenSpec suite [1], including also an IR mapper and a UV spectrometer [2] suite. The science objectives of this suite are to search for temporal variations in surface temperatures and tropospheric concentrations of volcanically emitted gases, indicative of volcanic eruptions; and study surface-atmosphere interactions and weathering by mapping surface emissivity and tropospheric gas abundances. Recent and perhaps ongoing volcanic activity has been inferred in data from both Venus Express and Magellan. Maintenance of the clouds requires a constant input of H2O and SO2. A large eruption would locally alter the composition by increasing abundances of H2O, SO2 and CO and perhaps decreasing D/H ratio. Observations of changes in lower atmospheric SO2, CO and H2O vapour levels, cloud level H2SO4 droplet concentration, and mesospheric SO2, are therefore required to link specific volcanic events with past and ongoing observations of the variable and dynamic mesosphere, to understand both the importance of volatiles in volcanic activity on Venus and their effect on cloud maintenance and dynamics. To contribute to this investigation, VenSpec-H is designed to measure H2O and HDO contents in the first scale height of Venus’ atmosphere and probe H2O, HDO, CO, OCS, SO2 in the 30 to 40 km altitude range [3-8]. To assess the performances of our instrument at detecting volcanic eruptions, we defined a couple of scenarios of plume releases and simulated the corresponding spectra. To simulate the vertical transport of the plume and the horizontal advection by the dynamics, the LMD Venus Mesoscale Model [9] is used, based on the WRF dynamical core and the Venus IPSL radiative transfer. The domain is focused on Imdr Regio, where VIRTIS observed a hotspot anomaly possibly linked to volcanic activity [10]. Tracers were added to the model representing H2O, CO and SO2. The chemistry and photodissociation sources and sinks are modelled by a linear relaxation of the tracer abundance toward a value representative of the deep atmosphere with a characteristic time. The deep atmosphere abundance is set to 130 ppm for SO2, 30 ppm for H2O and 20 ppm for CO. The relaxation time is set to 100 years for SO2, to 1000 years for CO and to 1 week, 1 month and 1 year for H2O representing the uncertainty of the chemistry timescale in that region. Several configurations are considered for the plume, an idealised set-up where the elevation height is fixed and the outgassing abundance is constant inside the plume and in time, and a more realistic set-up where a temperature and outgassing anomalies at the surface are prescribed is ongoing testing. The radiances of the nightside atmosphere of Venus originate from the thermal emission of the surface and atmosphere. The spectra were simulated from 1 to 2.5 microns, using ASIMUT-ALVL, a line-by-line radiative transfer code developed at BIRA-IASB [11]. CO2, H2O, HDO, CO, SO2, and OCS, as well as aerosols were included. The performances of the instrument will be described in terms of its capabilities to detect small variations in the atmosphere. References [1] J. Helbert et al., “The VenSpec suite on the ESA EnVision mission to Venus”, Proc. SPIE 11128, Infrared Remote Sensing and Instrumentation XXVII, 1112804 (2019). [2] E. Marcq et al., “Instrumental requirements for the study of Venus’ cloud top using the UV imaging spectrometer VeSUV”, Advances in Space Research, 68 (2021) 275-291. [3] B. Bézard et al., “Water vapor abundance near the surface of Venus from Venus Express/VIRTIS observations,” Journal of Geophysical Research, Planets, 114 (2009) E00B39. [4] B. Bézard et al., “The 1.10- and 1.18-μm nightside windows of Venus observed by SPICAV-IR aboard Venus Express,” Icarus, 216 (2011) 173–183. [5] A. Fedorova et al., “The CO2 continuum absorption in the 1.10-and 1.18-μm windows on Venus from Maxwell Montes transits by SPICAV IR onboard Venus Express,” Planetary and Space Science, 113 (2015) 66-77. [6] E. Marcq et al., “Remote sensing of Venus’ lower atmosphere from ground-based IR spectroscopy: latitudinal and vertical distribution of minor species,” Planetary and Space Science, 54 (2006) 1360-1370. [7] E. Marcq et al., “A latitudinal survey of CO, OCS, H2O,and SO2 in the lower atmosphere of Venus: spectroscopic studies using VIRTIS-H,” Journal of Geophysical Research, Planets, 113 (2008) E00B07. [8] E. Marcq et al., “Evidence for SO2 latitudinal variations below the clouds of Venus”, Astronomy & Astrophysics, 648 (2021) L8. [9] M. Lefèvre, A. Spiga and S. Lebonnois, “Mesoscale modeling of Venus' bow-shape waves”, Icarus, 335 (2019) 113376. [10] E. Smrekar, et al., “Recent Hotspot Volcanism on Venus from VIRTIS Emissivity”, Data. Science, 328 (2010) 605. [11] A.C. Vandaele, M. Kruglanski and M. De Mazière, “Modeling and retrieval of atmospheric spectra using ASIMUT”, Proc. of the First 'Atmospheric Science Conference', ESRIN, Frascati, Italy, 2006.

1. IntroductionVenus is hosting a global sulfuric acid cloud layer between 45 and 70 km which has been investi- gated by the Venus Express and Akatsuki mission as well as its coupling with the surface. One of the main questions that remains unclear about the dynamics of the Venusian atmosphere is how this convective cloud layer mixes momentum, heat, and chemical species and generates gravity waves. Several models have been developed to study these phenomenons. We proposed to use these models to study the impact of this turbulence on the chemical species, focusing on water and sulfuric dioxide. 2. ModelTo study the convective layer, a Large Eddy Simulations (LES) model [1] has been developed using the Weather-Research Forecast (WRF) non-hydrostatic dynamical core [2] coupled with the IPSL Venus GCM physics package [3]. The model is able to resolve a realistic convective layer between 47 and 55 km as well as one convective layer at cloud top altitudes (70 km) at the substellar point (Fig 1). Figure 1: Vertical cross-section of the vertical wind (m/s) at the Equator at noon. Between 47 and 55 km is the main convective layer, between 55 and 67 km are the gravity waves induced by convection and between 67 and 73 is the cloud top convective layer presents only at the substellar point. Tracers has been included in the model representing H2O and SO2, the chemistry and photodissociation sources and sinks are modeled by a linear relaxation of the tracer abundance toward a prescribed vertical profile with a characteristic time. The relaxation time ranges from 102 to 106 s. The prescribed vertical tracer profiles are constructed using observed abundance visible in Fig 2. Figure 2: Vertical profile of the tracer abudance relaxation profile. The black represents the value for the deep atmosphre [4], the star is the SO2 ground based observations at 65 km [5] and the circle is the cloud top H2O Venus Express value [6, 7]. 3. ResultsThis simple model is able to determine the vertical mixing for SO2 and H2O in the cloud layer, and for which chemical timescale the convection plays an important role. The resolution of 500 m allow an estimate of the horizontal turbulent spatial features, induced by the convection and gravity waves, for SO2 and H2O. References[1] Lefèvre et al., JGR : Planets, 123, 2773-2789, 2018.[2] Skamarock, W. C. and J. B. Klemp, J., Comput. Phys., 227, 3465-3485, 2008[3] Garate-Lopez, I. and Lebonnois., S., Icarus, 314,1-11, 2018.[4] Bézard, B. and De Bergh, C., JGR : Planets, 112, 2007.[5] Encrenaz, T. et al., A. & A., 595, 2016.[6] Fedorova, A. et al., Icarus, 275, 143-162, 2016.[7] Cottini., V. et al., Icarus, 217, 561-569, 2012.

This work aims to determine the mass-radius rela-tionships of highly irradiated (500< Tirr We show that these planets, even with smallwater contents, can become strongly inflated andproduce large radii for small masses.We alsoshow that strongly irradiated small planets cannotsustain their atmospheres due to the lack of hy-drostatic stability, implying they cannot preserveany hydrosphere. The temperature and the watermass fraction are the key parameters controllingthe extent of inflation and the thickness of thesupercritical layer. An important amount of wateralso leads to the contraction of the rocky interior.However, the composition of the rocky interioronly has a limited impact on the final mass-radiusrelationship, and barely impacts the behavior of thehydrosphere.

The increasing number of well characterised low-mass planets, combined with the valuable informations from stellar and planetary spectroscopy, opens the way to the modeling of planetary structures and compositions, which can be obtained with theoretical and numerical works. This approach gives a valuable insight to understand the formation of planetary systems in the low-mass range. We present a 1D planetary model where the interior is coupled with the atmosphere in radiative-convective equilibirum within a Bayesian retrieval scheme. In addition to a Fe core and a silicate mantle, we take into account water in all its possible phases, including steam and supercritical phases, which is necessary for systems with a wide range of stellar irradiations. Our interior-atmosphere model calculates the compositional and atmospheric parameters, such as Fe and water content, surface pressures, scale heights and albedos. We analyse the multiplanetary systems K2-138 and TRAPPIST-1, which present six low-mass planets with different densities and irradiations. From the individual composition of their planets, we derive a similar trend for both systems: a global increase on the water content with increasing distance from the star in the inner region of the systems, while the planets in the outer region present a constant water mass fraction. This trend reveals the possible effects of migration, formation location and atmospheric mass loss during their formation history.

Massive and water-rich planets should be ubiquitous in the universe. Many of those worlds are expected to be subject to important irradiation from their host star, and display supercritical water layers surrounded by extended steam atmospheres. Irradiated ocean planets with such inflated hydrospheres have been recently shown to be good candidates for matching the mass-radius distribution of sub-Neptunes. Here we describe a model that computes a realistic structure for water-rich planets by combining an interior model with an updated equation of state (EoS) for water, and an atmospheric model that takes into account radiative transfer. We find that the use of non appropriate EoSs can lead to the overestimation of the planetary radius by up to $\sim$10\%, depending on the planet size and composition. Our model has been applied to the GJ 9827 system as a test case and indicates Earth- or Venus-like interiors for planets b and c, respectively. Planet d could be an irradiated ocean planet with a water mass fraction of $\sim$$20\pm10\%$. We also provide fits for the mass-radius relationships, allowing one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. Our calculations finally suggest that highly irradiated planets lost their H/He content through atmospheric loss processes, and that the leftover material led to either super-Earths or sub-Neptunes, depending on the water mass fraction., Accepted for publication in ApJ

Context. Sulphur dioxide (SO2) is highly variable above the clouds of Venus, yet no spatial or temporal variability below the clouds had been known until now. Aims. In order to constrain Venus’s atmospheric circulation and chemistry (including possible volcanic outgassing), more accurate SO2 measurements below the clouds are therefore needed. Methods. We used the high-resolution iSHELL spectrometer located at the NASA IRTF to record thermal night-side spectra, which we fitted using an updated forward radiative transfer model that was previously employed to process SpeX/IRTF and VIRTIS-H/Venus Express spectra. Results. We report, for the first time, an increase in SO2 with increasing latitude (+30% between the minimum near 15°S and > 35°N). This is consistent with the interaction between the Hadley-cell circulation and a postulated vertical profile in SO2 estimated to increase between 30 and 40 km in altitude, as previously suggested by in situ ISAV measurements. Conclusions. This SO2 variability challenges our current understanding of Venus’s tropospheric thermochemistry and underlines the high scientific return from high-resolution spectroscopy from, for example, future orbiters.

International audience; Ultraviolet spectral imaging has been a powerful tool to investigate the cloud top of Venus, allowing for measurement of several minor gases (especially SO2, SO, O3), of cloud top aerosol’s microphysical properties and of atmospheric dynamics through tracking of the unevenly distributed UV absorber. After a brief review of recent UV instruments that orbited around Venus, we present the results of a state-of-the-art radiative transfer model from Marcq et al. (2020) to derive the spectral resolution and Signal-to-Noise ratio (SNR) required to derive abundances of these gases, retrieve optical properties of the aerosols beyond our current knowledge. This leads us to propose a two-channel UV hyperspectral push-broom imager called VeSUV (standing for Venusian Spectroscopy in UV) whose technical characteristics will improve on existing measurements by a factor of at least 2, and which is well suited to the integration into the payload of future low Venus orbit platforms such as the proposed EnVision mission to ESA M5 call.

Understanding Venus will benefit from a dedicated effort through an international program of missions that are coordinated and offering opportunities for coooperation. The recent discovery of phosphene in the Venus clouds and possibility of life will increase the exploration missions and cooperation and coordination will be very benefical.

International audience; The nighttime ozone and sulfur dioxide distributions were analyzed using the entire SPICAV‐UV/Venus Express stellar occultation dataset. After the discovery of an ozone layer at 100 km in the mesosphere reported by Montmessin et al. (2011), 132 other detections were made during the entire 8 years long observing period of the SPICAV UV instrument. In the rare detections the peak abundances of O3 accumulating in the mesosphere are observed with densities from 107 to 108 molecules⋅cm‐3 at 85‐110 km. The ozone layer is estimated to vary from 1 ppbv to 30 ppbv at 85‐95 km while at 95‐105 km the VMR is expected within an interval from 6 ppbv to 120 ppbv. Below 93 km, a puzzling decrease of mixing ratio is observed toward midnight at 30°N. Our work also provides an improved sequel to the analysis of the sulfur dioxide survey previously made in the upper mesosphere by Belyaev et al. (2017). On average, the SO2 content is found to remain constant throughout the vertical profile at a value of around 135±21 ppbv between 85 and 100 km. Rapid and large variations prevent to conclude firmly on any time or space pattern of SO2.

We present an atmospheric characterization study of two medium sized planets bracketing the radius of Neptune: HD 106315 c (R$_{\rm{P}}$=4.98 $\pm$ 0.23 R$_{\oplus}$) and HD 3167 c (R$_{\rm{P}}$=2.740$_{-0.100}^{+0.106}$ R$_{\oplus}$). We analyse spatially scanned spectroscopic observations obtained with the G141 grism (1.125 - 1.650 $\mu$m) of the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope. We use the publicly available Iraclis pipeline and TauREx3 atmospheric retrieval code and we detect water vapor in the atmosphere of both planets with an abundance of $\log_{10}[\mathrm{H_2O}]=-2.1^{+0.7}_{-1.3}$ ($\sim$5.68$\sigma$) and $\log_{10}[\mathrm{H_2O}]=-4.1^{+0.9}_{-0.9}$ ($\sim$3.17$\sigma$) for HD 106315 c and HD 3167 c, respectively. The transmission spectrum of HD 106315 c shows also a possible evidence of ammonia absorption ($\log_{10}[\mathrm {NH_3}]=-4.3^{+0.7}_{-2.0}$, $\sim$1.97$\sigma$ -even if it is not significant-), whilst carbon dioxide absorption features may be present in the atmosphere of HD 3167 c in the $\sim$1.1-1.6~$\mu$m wavelength range ($\log_{10}[\mathrm{CO_{2}}]= -2.4^{+0.7}_{-1.0}$, $\sim$3.28$\sigma$). However the CO$_2$ detection appears significant, it must be considered carefully and put into perspective. Indeed, CO$_2$ presence is not explained by 1D equilibrium chemistry models, and it could be due to possible systematics. The additional contribution of clouds, CO and CH$_4$ are discussed. HD 106315 c and HD 3167 c will be interesting targets for upcoming telescopes such as the James Webb Space Telescope (JWST) and the Atmospheric Remote-Sensing Infrared Exoplanet Large-Survey (Ariel)., Comment: Accepted for publication in AJ

Context. LHS 1140 is an M dwarf known to host two transiting planets at orbital periods of 3.77 and 24.7 days. They were detected with HARPS and Spitzer. The external planet (LHS 1140 b) is a rocky super-Earth that is located in the middle of the habitable zone of this low-mass star. All these properties place this system at the forefront of the habitable exoplanet exploration, and it therefore constitutes a relevant case for further astrobiological studies, including atmospheric observations. Aims. We further characterize this system by improving the physical and orbital properties of the known planets, search for additional planetary-mass components in the system, and explore the possibility of co-orbitals. Methods. We collected 113 new high-precision radial velocity observations with ESPRESSO over a 1.5-yr time span with an average photon-noise precision of 1.07 m s-1. We performed an extensive analysis of the HARPS and ESPRESSO datasets and also analyzed them together with the new TESS photometry. We analyzed the Bayesian evidence of several models with different numbers of planets and orbital configurations. Results. We significantly improve our knowledge of the properties of the known planets LHS 1140 b (Pb ∼ 24.7 days) and LHS 1140 c (Pc ∼ 3.77 days). We determine new masses with a precision of 6% for LHS 1140 b (6.48 ± 0.46 Mpdbl) and 9% for LHS 1140 c (mc = 1.78 ± 0.17 Mpdbl). This reduces the uncertainties relative to previously published values by half. Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140 b might be iron-enriched and LHS 1140 c might be a true Earth twin. In both cases, the water content is compatible to a maximum fraction of 10-12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet LHS 1140 b. Our results also provide evidence for a new planet candidate in the system (md = 4.8 ± 1.1Mpdbl) on a 78.9-day orbital period, which is detected through three independent methods. The analysis also allows us to discard other planets above 0.5 Mpdbl for periods shorter than 10 days and above 2 Mpdbl for periods up to one year. Finally, our co-orbital analysis discards co-orbital planets in the tadpole and horseshoe configurations of LHS 1140 b down to 1 Mpdbl with a 95% confidence level (twice better than with the previous HARPS dataset). Indications for a possible co-orbital signal in LHS 1140 c are detected in both radial velocity (alternatively explained by a high eccentricity) and photometric data (alternatively explained by systematics), however. Conclusions. The new precise measurements of the planet properties of the two transiting planets in LHS 1140 as well as the detection of the planet candidate LHS 1140 d make this system a key target for atmospheric studies of rocky worlds at different stellar irradiations., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

Small planets (1-3.9 Rearth) constitute more than half of the inventory of the 4000-plus exoplanets discovered so far. Smaller planets are sufficiently dense to be rocky, but those with radii larger than 1.6 Rearth are thought to display in many cases hydrogen/helium gaseous envelopes up to 30% of the planetary mass. These low-mass planets are highly irradiated and the question of their origin, evolution, and possible links remains open. Here we show that close-in ocean planets affected by greenhouse effect display hydrospheres in supercritical state, which generate inflated atmospheres without invoking the presence of large hydrogen/helium gaseous envelopes. We present a new set of mass-radius relationships for ocean planets with different compositions and different equilibrium temperatures, which are found to be well adapted to low-density sub-Neptune planets. Our model suggests that super-Earths and water-rich sub-Neptunes could belong to the same family of planets, i.e. hydrogen/helium-free planets, with differences between their interiors simply resulting from the variation in the water content.

Introduction: The Venus Emissivity Mapper is the first flight instrument designed to focus on mapping the surface of Venus using several atmospheric windows around 1 µm. After years of development, VEM now has a mature design. An existing laboratory prototype has verified an achievable instrument SNR of well above 1000, as well as predicted error in retrieval of relative emissivity of better than 1%, assuming the availability of improved Venus topography.VEM science goals: The instrument will provide a global map of rock type from orbit, assessing iron contents and the redox state of the surface by observing the surface with six narrow band filters, ranging from 0.86 to 1.18 µm. Three additional windows allow corrections for cloud composition and variability, two measure water abundance, and three compensate for stray light. Continuous observation of Venus’ thermal emission will also place tighter constraints on current volcanic activity. Eight channels provide measurements of atmospheric water vapor abundance as well as cloud microphysics and dynamics, permitting accurate correction of atmospheric interference on the surface data.The instrument is currently part of two Phase A studies: is part of the payload of the NASA VERITAS mission as well as of the ESA EnVision mission, here as the VenSpec-M channel in the VenSpec spectrometer suite. Combining VEM with a high-resolution radar mapper will provide key insights into the divergent evolution of Venus and Earth. Flying VEM on more than one mission will enable a long timeline of monitoring for volcanic activity on Venus. Combined with the existing VenusExpress data, VEM enables detection and mapping of surface changes over decades.VEM Design: The VEM system design is a pushbroom multispectral imaging system. It leverages a proven measurement technique pioneered by VIRTIS on Venus Express (VEX). It also incorporates lessons learned from VIRTIS to achieve greatly improved sensitivity and spectral and spatial coverage:A filter array (rather than a grating) provides wavelength stability (band-center and width-scatter) ~5× more stable and maximizes signal to the focal-plane array (FPA). Spectral windows below 1µm are covered for the first time. A two-stage baffle decreases scattered light and improves sensitivity. Use of an InGaAs detector with an integrated thermal electric cooler (TEC) eliminates the need for cryogenic cooling. The design maturity, combined with a standard camera optical design, leads to low development risk.VEM prototyping: VEM has been under development for several years with significantly financial investment from DLR. Following creation of the first breadboard model in 2015 during Phase A for the NASA Discovery proposal VERITAS, a laboratory prototype (LP) of the VEM instrument has been developed. This prototype includes the development version of the VEM optics with a filter array with two active filter strips. The optics underwent a set of calibration measurements on sub-unit level at LATMOS prior to delivery to DLR. All key optical design parameters including transmission and wavelength coverage have been verified using the VEMO prototype.A first performance evaluation of the VEM prototype used two Venus analog samples heated to Venus surface temperatures. This was performed using the Venus simulations setup at the Planetary Spectroscopy Laboratory with the prototype mounted on the chamber. The retrieved emissivities match laboratory values, and uncertainty for a single unbinned exposure is VEM atmospheric correction: Methodology for retrieving surface emissivity is complex but well understood and demonstrated. To distinguish between surface and atmospheric contributions, VEM uses an updated version of the extensively tested pipeline developed to process VIRTIS data, combined with a radiative transfer model (RTM). Surface emissivity retrieval techniques were developed based on Galileo NIMS observations at 1700, 1800 and 2300 nm. VEM cloud bands occur at 1195, 1310, and 1510 nm, the first on the flank of the 1180‑nm surface windows. VEM’s cloud bands are close to surface bands, providing near-optimal correction. Only relative emissivity measurements are needed to calculate the spectral slope to meet our surface emissivity requirements. We do not have a requirement on the accuracy of the retrieved emissivity. However, we can now tie an emissivity retrieval to in situ measurements to assess accuracy. For this comparison, the Venera 9 and 10 landing sites (not observed by VIRTIS) will be observed by VEM both on EnVision and on VERITAS.VEM observes each spot on the surface multiple times. Therefore both atmospheric and instrument noise are reduced by averaging image swaths acquired at different times. Applying the updated analysis of atmospheric error for VEM parameters and taking multiple-look averaging into account, our capability for emissivity precision is better than 1.5% for all bands and better than 1% in most bands.Conclusion: VEM builds on recent advances in the laboratory analog spectroscopy at PSL at DLR. It is the first flight instrument designed to focus on mapping the surface of Venus using atmospheric windows around 1 µm. VEM has a mature design with an existing laboratory prototype that verifies an achievable instrument SNR of >1000, as well as a predicted error in the retrieval of relative emissivity of better than 1%.

Planetary interior models rely on the thermodynamic properties of the used materials. Equations of states (EOSs) are key ingredients to compute internal structures, as they link the pressure and density profiles, and leave a unique solution satisfying all equations describing the interior of the planet. Often, when thermodynamic data are lacking, the formulation of EOSs allow extrapolation in both pressure and temperature. The effect of temperature on EOSs is often minor, implying that models of isothermal planets provide consistent results. This approach meets limitations in the case of fluids (liquids, gases and supercritical fluids), whose properties are very sensitive to variations in temperature. Here we propose a way to compute the relevant thermodynamic parameters in supercritical water from the most recent EOSs, in order to compute the internal structures of irradiated ocean planets, coupled with a 1D convective-radiative atmospheric model. Our results allow a better understanding of the diversity of observed sub-Neptunes, linking their internal structure to formation conditions.

Instrument description The VenSpec-U instrument is a dual channel UV spectral imager (low and high spectral resolution channels, “LR” and “HR” hereafter), part of the VenSpec spectrometer suite on board the proposed Venus orbiter EnVision. Each channel consists of an entrance baffle, an objective composed of two lenses and a stop diaphragm, and a spectrometer composed of a slit and a toroidal holographic grating. It also includes s shortpass filter to reject the wavelengths above the higher limit of both channel bands and a zero-order trap to avoid straylight due to internal reflexions of the grating zero-order. The optical layout is presented in Figure 1. Both LR and HR slits are parallel and the optical layout is such that both channels have the same instantaneous field of view (FoV), allowing simultaneous observations and calibrations. Each slit image is then spectrally dispersed by its respective toroidal holographic grating and is formed on a shared CMOS back-side illuminated detector. Figure 1: VenSpec-U optical layout overview, with the HR and LR channels respectively on the left and on the right. The narrow-slit axis of the detector contains the spectral information, whereas the long-slit axis contains the spatial information along the 22.5° FoV of each slit. The spectra of LR and HR channels are dispersed one above the other on the focal plane. The remaining spatial direction is provided through orbital scrolling (“pushbroom” strategy). Binning on the spatial axis is performed on the detector. The detector will be controlled such that the integration time and the binning scheme is adjusted independently (and simultaneously) for each channel giving high flexibility and providing parameters for the optimisation of each acquisition. Instrument Performance the HR channel (210-240 nm) at 0.2 nm spectral resolution and spatial sampling not coarser than 36 km (12 km target) should reach a SNR of at least 100; the LR channel (190-380 nm) at 2 nm spectral resolution and spatial sampling not coarser than 6 km (3 km target) should reach a SNR of at least 200. According to our forward model based on HST-STIS [Jessup et al., 2015] and SPICAV-UV heritage [Marcq et al., 2020], this shall be sufficient to measure the targeted species (SO, SO2, UV absorber) with a relative accuracy better than 25%. These measurements shall allow to characterize variability of Venus cloud top on temporal scales ranging from hours to years and spatial scales ranging from a few kilometers to planetary scale in relation to the climate and/or present day volcanic activity of Venus. Bibliography K. L. Jessup et al., Coordinated Hubble Space Telescope and Venus Express Observations of Venus’ upper cloud deck, Icarus 258, 2015 E. Marcq et al., Climatology of SO2 and UV absorber at Venus’ cloud top from SPICAV-UV nadir dataset, Icarus 335, 2020

If Venus were a newly discovered exoplanet, it would be one of the most Earth-like yet identified. Its similarity in size, bulk density and cloud top temperatures give no clue to the hellish temperatures at its surface. Venus hosts an array of geological features as complex as Earth, but without its organisation, and sustains a chemically reactive atmosphere, but without life. Proposed in response to ESA’s M5 call, with enabling support from NASA, EnVision is currently in Phase A study for the next medium-class mission opportunity proceeding towards a final mission selection in summer 2021 for a launch in 2032. Here we discuss the science questions motivating the mission in more detail. Building on discoveries from Magellan, Venus Express and Akatsuki, EnVision will focus on three overarching questions: Is Venus geodynamically active? How did Venus arrive at its current state? How does the Venus climate work and how do the interior, surface and atmosphere interact? 1 – Is Venus geodynamically active? Venus should be geologically active today and its globally young surface implies extensive volcanic resurfacing, but whether this happened in episodic global events or in a continuous process of small-scale resurfacing is uncertain. Constraining the rate of volcanic and tectonic activity can reveal whether Venus occupies one of these end members, or lies somewhere on the spectrum between. Magellan radar image mosaic of a 550 km wide region of Lada Terra (47°S, 25°E) showing a system of radar-bright and dark lava flows breaching a ridge belt and ponding in a large radar-bright deposit covering 100,000 km². Ammavaru, the source caldera, lies 300 km to the west (JPL/Caltech). Understanding the tectonic regime driving resurfacing and heat loss is as important as knowing the rate of activity. The surface appears partitioned into areas of low strain bounded by narrow high strain margins. The abundance of steep slopes and landslides implies active uplift in these high strain areas, but existing data provide no constraint on the frequency of landslides or rates of tectonic movement. Are the low strain regions actively created and destroyed, like Earth’s oceanic plates, or simply mobilised locally? What is the significance of the global network of elevated rift systems and linear lowland wrinkle-ridged plains? Unique to Venus are coronae, quasi-circular volcano-tectonic features, typically 100–500 km across. Are they the surface expression of plumes, or magmatic intrusions, or subduction zones? The processes of weathering, mass wasting and aeolian transport are critical for understanding both the geological history and climatic evolution of Venus. Venus Express found anomalously high IR emissivities near suspected active volcanoes, interpreted as fresh, unweathered lava flows, but both their mineralogy and the weathering processes involved are unknown. Magellan detected several, probably impact-related, dune fields at the limit of its resolution, and found indirect evidence for globally distributed smale-scale ripples. 2 – How Did Venus Arrive at its Current State? The cratering record reveals that the Venus surface is, on average, under 1 Ga old. While some areas are likely active today, other regions, e.g. the tessera highlands, may be considerably older. Magellan data imply a variety of age relationships and long-term activity, with a non-random association between geological features and elevation, e.g. the uplands are consistently more deformed than the lowlands. Impact craters themselves show alteration to dark floors, perhaps from airfall deposits or magmatic resurfacing. Densely fractured plains (right) abutting tessera (bottom); both are embayed by younger plains (dark areas). A steep-sided volcanic dome (upper left) may be the source of the plains or unrelated to them, and older or younger than the tesserae. Magellan image at 46°N, 360°E, after Basilevsky and McGill (2007). Constraining the history is critical to understanding not only when and how resurfaced, but whether that activity has changed systematically through time. Were the plains formed in a short period by massive outpourings or by many thousands of small flows over their entire history? Or did many different mechanisms – including sedimentary processes – operate at different times and places? Globally, Venus exhibits perhaps even more tectonic deformation than Earth: what is its role in resurfacing the planet and have the regimes of tectonic deformation changed over time? How did tesserae, especially, accumulate their extraordinary degree of deformation? The interior of Venus is probably Earth-like, but not the same; its core size is poorly constrained by Magellan gravity data. These data are consistent with an organised pattern of mantle convection but lack the resolution necessary to connect it with geological-scale features. 3 - How does the Venus climate work and how do the Interior, Surface and Atmosphere Interact? How and why the atmospheres of two Earth-like planets evolved so differently is one of the many compelling reasons to study Venus, directly addressing the question of how our own world became habitable. Understanding its evolution depends on knowing the exchanges between its interior, surface and space. The lower/middle clouds of Venus as imaged by Akatsuki IR2 camera. Dark areas represent thicker clouds, which may represent volcanic plumes of ash or sulphate particulates. (JAXA/ISAS/DART/Damia Bouic) Models suggest that the clouds are maintained by a constant input of H2O and SO2, both of which vary considerably, perhaps because of volcanic emissions. Elevated D/H ratios indicate the loss of early oceans, but the ‘starting’ mantle D/H ratio is unknown. Identification of granites in the ancient highlands would support this inference, but the direct detection and characterisation of volcanic volatiles is key to inferring past climate evolution. Beyond the specific investigations outlined above, however, the most important unknown factor in determining the present day state of Venus and its atmosphere, and how it arrived at that state, is the interaction between the interior, surface and atmosphere: the whole being more than the sum of the parts. References Basilevsky and McGill (2007), Surface evolution of Venus, in Exploring Venus as a Terrestrial Planet, Geophysical Monograph Series 176, edited by L. W. Esposito, E. R. Stofan and T. E. Cravens, pp. 23-43, American Geophysical Union, Washington, DC

Small planets ($\sim$1--3.9 $\Rearth$) constitute more than half of the inventory of the 4000-plus exoplanets discovered so far. Smaller planets are sufficiently dense to be rocky, but those with radii larger than $\sim$1.6 $\Rearth$ are thought to display in many cases hydrogen/helium gaseous envelopes up to $\sim$30\% of the planetary mass. These low-mass planets are highly irradiated and the question of their origin, evolution, and possible links remains open. Here we show that close-in ocean planets affected by greenhouse effect display hydrospheres in supercritical state, which generate inflated atmospheres without invoking the presence of large hydrogen/helium gaseous envelopes. We present a new set of mass-radius relationships for ocean planets with different compositions and different equilibrium temperatures, which are found to be well adapted to low-density sub-Neptune planets. Our model suggests that super-Earths and water-rich sub-Neptunes could belong to the same family of planets, i.e. hydrogen/helium-free planets, with differences between their interiors simply resulting from the variation in the water content., Accepted for publication in The Astrophysical Journal Letters

Since January 2012, we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). Here, we present new data recorded in February and April 2019 in the 1345 cm−1(7.4μm) spectral range, where SO2, CO2, and HDO (used as a proxy for H2O) transitions were observed. The cloud top of Venus was probed at an altitude of about 64 km. As in our previous studies, the volume mixing ratio (vmr) of SO2was estimated using the SO2/CO2line depth ratio of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2line depth ratio, assuming a D/H ratio of 200 times the Vienna standard mean ocean water. As reported in our previous analyses, the SO2mixing ratio shows strong variations with time and also over the disk, showing evidence for the formation of SO2plumes with a lifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We have used the 2019 data in addition to our previous dataset to study the long-term variations of SO2and H2O. The data reveal a long-term anti-correlation with a correlation coefficient of −0.80; this coefficient becomes −0.90 if the analysis is restricted to the 2014–2019 time period. The statistical analysis of the SO2plumes as a function of local time confirms our previous result with a minimum around 10:00 and two maxima near the terminators. The dependence of the SO2vmr with respect to local time shows a higher abundance at the evening terminator with respect to the morning. The dependence of the SO2vmr with respect to longitude exhibits a broad maximum at 120–200° east longitudes, near the region of Aphrodite Terra. However, this trend has not been observed by other measurements and has yet to be confirmed.

International audience; Large planetesimals and planetary embryos ranging from several hundred to a few thousand kilometers can develop magma oceans through mutual collisions, gravitational energy, and the heating of short-lived radioactive elements. During their solidification after the dissipation of the disk a steam atmosphere will be catastrophically outgassed and may be lost efficiently via hydrodynamic escape, as long as it does not condense. The escaping H-atoms that originate from the dissociation of H2O and H2 will drag heavier trace elements like noble gases such as Ne and Ar and outgassed moderately volatile rock-forming elements such as K, Na, Si, Mg, etc. into space. Under consideration of various EUV flux evolution scenarios of young solar-type stars, we apply an upper atmosphere hydrodynamic escape model that includes the dragging of heavier species by escaping H-atoms. We investigate the atmospheric/elemental escape and fractionation from planetary embryos with masses of 1 MMoon, 0.5 MMars, 1 MMars, and 1.5 MMars at different orbital distances between the orbits of Venus and Mars. Our results indicate that the steam atmospheres and the embedded trace elements will be lost efficiently before they condense for masses ≤0.5 MMars and orbital distances up to 1 AU. For heavier embryos of up to 1.5 MMars almost all of the considered steam atmospheres can be lost within ≈12 Myr, which lies within the time frame of the formation of the first Martian protocrust after ≈20 Myr, i.e. for such steam atmospheres to be lost completely a shallow magma ocean must remain below the atmosphere, which might be achieved through frequent impacts onto the planetary embryo. The considered outgassed noble gases and rock-forming elements will be completely dragged away together with the steam atmospheres under the assumption that the trace elements will reach the thermosphere. For embryos with masses ≤MMoon the gravity is too weak for a dense atmosphere to build up for the high magma ocean related surface temperatures and all outgassed elements will escape immediately to space. For all considered planetary masses and orbits the loss rates of Ar and Ne are so high that there will be no fractionation of their isotopes. The studied planetary embryos, even though not isotopically fractionated, will therefore be severely depleted in noble gases and moderately volatile elements. Hydrodynamic escape might then also affect the final composition of terrestrial planets that accrete out of such planetary embryos, such as the volatile content and the Fe/Mg ratio of a planet.

International audience; Hubble Space Telescope Imaging Spectrograph (HST/STIS) observations were obtained on 3 dates in December 2010 and January 2011 recording the cloud top properties over Aphrodite Terra and a low elevation region downwind of Aphrodite through LSTs extending from 7 to 11 a.m. From these data we trace the cloud top sulfur-oxide chemistry and UV albedo sensitivity to LST, latitude and topography. Above regions co-located in LST and latitude, albedo variations observed at 245 nm parallel those observed at 365 nm-following the pattern expected from Hadley cell circulation. However, darkening of the cloud top albedo at LSTs between 9.5 and 11 h beyond that expected from simple Hadley circulation was also observed. Above the plains the albedo darkening intensified rapidly with LST and was observed at latitudes extending as high as ~30 N; however, above the mountains the darkening was either entirely absent or evident only at 0 N at an intensity 2× lower than that observed over the plains. Because the observed 245 nm albedo LST variations were inconsistent with that expected from multiple scattering of the coincidently retrieved SO2 gas abundance, we conclude that the 245 nm albedo is diagnostic of the vertical and spatial distribution, abundance (and potentially the identity) of Venus' unidentified UV absorber—rather than SO2 gas. The LST albedo trends are best explained by the onset of subsolar convective activity that intensifies with LST expanding vertically from the boundary between the middle and upper clouds to the cloud tops and increasing the detectability of the unknown absorbing species at the cloud tops. The terrain dependence in the observed intensity implies the time at which the expansion reaches the cloud tops is later above the mountains than over the plains. Additionally, at the time of observation, the low-latitude large-scale vertical mixing rates that control the latitudinal gradients of the SO2 and unknown absorber abundances above and within the cloud top region were lower over Aphrodite Terra than the plains, to the extent that photochemical processing destroyed the spatial correlation between those absorbing species. These observations show the power of UV spectroscopy to diagnose the distinct influences of deep (Hadley-cell type) and shallow convective mixing processes on the vertical and horizontal distribution of Venus' unknown absorbing species, and the sensitivity of these processes to LST and topography, relative to the sulfur oxide chemistry. These results are essential for accurate climate modeling—and when compared to recent Venus missions motivate a need for additional follow-on observing campaigns that simultaneously trace key cloud top chemistry and dynamic processes including the LST dependent evolution of planetary scale gravity waves (GWs). With the inevitable aging of the Hubble Telescope, follow-on observations providing temporally coincident traces of the cloud top albedo, sulfur-oxide chemistry and GW features will require a new age of space-based telescopes and Venus orbiting mission with sensitivity to UV, visible and IR wavelengths.

Following the announcement of the detection of phosphine (PH$_3$) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the infrared range. Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO$_2$ and H$_2$O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm$^{-1}$ where a PH$_3$ transition is present. From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-$\sigma$ upper limit of 5 ppbv for the PH$_3$ mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths. Our result brings a strong constraint on the maximum PH$_3$ abundance at the cloud top and in the lower mesosphere of Venus., Comment: Astronomy & Astrophysics, in press

International audience; Following our previous work (Marcq et al., 2013, Marcq et al., 2011), we have updated our forward radiative transfer code and processed the whole SPICAV-UV/Venus Express nadir dataset (2006-2014) in order to retrieve SO2 abundance at cloud top – assuming a SO2 decreasing scale height of 3 km and a ratio SO/SO2 tied to 10% – as well as the imaginary index of scattering mode 1 particles, representative of the remaining UV absorption, since the OSSO vertical profile found by Frandsen et al. (2016) cannot account for our observations. Our main results mostly confirm and extend the validity of those discussed by Marcq et al. (2013), namely: (i) long-term variations of low latitude SO2 at 70 km between ∼ 100 ppbv (2007, 2009) and less than 10 ppbv (2014); (ii) in average, decreasing SO2 with increasing latitude and depletion near the sub-solar point, consistent with a competition between advection and photo-chemical destruction; (iii) secular increase of mode 1 imaginary index at 250 nm, from 10−2 to 5 ⋅ 10−2 between 2006 and 2010; (iv) if not related instead to long-term variability, a possible localized enrichment of SO2 and UV brightness increase above the western slopes of Aphrodite Terra, consistent with Bertaux et al. (2016) supply mechanism through orographic gravity waves. This spatial and temporal variability underlines the need for a long term monitoring of Venus SO2 and cloud top from ground-based facilities until the next generation of Venusian orbiters is operational.

How the volatile content influences the primordial surface conditions of terrestrial planets and, thus, their future geodynamic evolution is an important question to answer. We simulate the secular convective cooling of a 1-D magma ocean (MO) in interaction with its outgassed atmosphere. The heat transfer in the atmosphere is computed either using the grey approximation or using a k-correlated method. We vary the initial CO2 and H2O contents (respectively from 0.1 × 10−2 to 14 × 10−2 wt % and from 0.03 to 1.4 times the Earth Ocean current mass) and the solar distance—from 0.63 to 1.30 AU. A first rapid cooling stage, where efficient MO cooling and degassing take place, producing the atmosphere, is followed by a second quasi steady state where the heat flux balance is dominated by the solar flux. The end of the rapid cooling stage (ERCS) is reached when the mantle heat flux becomes negligible compared to the absorbed solar flux. The resulting surface conditions at ERCS, including water ocean's formation, strongly depend both on the initial volatile content and solar distance D. For D > DC, the “critical distance,” the volatile content controls water condensation and a new scaling law is derived for the water condensation limit. Although today's Venus is located beyond DC due to its high albedo, its high CO2/H2O ratio prevents any water ocean formation. Depending on the formation time of its cloud cover and resulting albedo, only 0.3 Earth ocean mass might be sufficient to form a water ocean on early Venus.

This paper presents an updated version of the simple 1D radiative-convective H2O-CO2 atmospheric model from Marcq [2012] and used by Lebrun et al. [2013] in their coupled interior-atmosphere model. This updated version includes a correction of a major miscalculation of the outgoing longwave radiation (OLR), and extends the validity of the model (P-coordinate system, possible inclusion of N2, improved numerical stability). It confirms the qualitative findings of Marcq [2012], namely (1) the existence of a blanketing effect in any H2O-dominated atmosphere: the outgoing longwave radiation (OLR) reaches an asymptotic value, also known as Nakajima's limit and first evidenced by Nakajima et al. [1992], around 280W/m2 neglecting clouds, significantly higher than our former estimate from Marcq[2012]. (2) The blanketing effect breaks down for a given threshold temperature Tϵ, with a fast increase of OLR with increasing surface temperature beyond this threshold, making extrasolar planets in such an early stage of their evolution easily detectable near 4μm provided they orbit a red dwarf. Tϵ

During accretion, the young rocky planets are so hot that they become endowed with a magma ocean. From that moment, the mantle convective thermal flux control the cooling of the planet and an atmosphere is created by outgassing. This atmosphere will then play a key role during this cooling phase. Studying this cooling phase in details is a necessary step to explain the great diversity of the observed telluric planets and especially to assess the presence of surface liquid water. We used here a radiative-convective 1D atmospheric model (H2O, CO2) to study the impact of the Bond albedo on the evolution of magma ocean planets. We derived from this model the thermal emission spectrum and the spectral reflectance of these planets, from which we calculated their Bond albedos. Compared to Marcq et al. (2017), the model now includes a new module to compute the Rayleigh scattering, and state of the art CO2 and H2O gaseous opacities data in the visible and infrared spectral ranges. We show that the Bond albedo of these planets depends on their surface temperature and results from a competition between Rayleigh scattering from the gases and Mie scattering from the clouds. The colder the surface temperature is, the thicker the clouds are, and the higher the Bond albedo is. We also evidence that the relative abundances of CO2 and H2O in the atmosphere strongly impact the Bond albedo. The Bond albedo is higher for atmospheres dominated by the CO2, better Rayleigh scatterer than H2O. Finally, we provide the community with an empirical formula for the Bond albedo that could be useful for future studies of magma ocean planets., 16 pages, 10 figures, 5 tables. Accepted for publication in the Journal Icarus the 27 August 2018

International audience; After the first sporadic detections of an ozone (O33 volume mixing ratio peaks in the 10 to 20 ppbv range, yielding observable column densities in the 0.1 to 0.5 Dobson units (DU), comparable to nominal values on Mars but much smaller than for Earth ( ∼ 300 DU). These measurements are supported by our 3D-photochemical model coupled with the LMD-IPSL GCM (Lebonnois et al., 2010), which indicates that the ozone layer identified by SPICAV results from downward transport of O2 ( ∼ 50 ppmv) molecules over the poles by the mean meridional circulation. Our findings do not contradict previous upper limits (

Since January 2012 we have been monitoring the behavior of sulfur dioxide and water on Venus, using the Texas Echelon Cross-Echelle Spectrograph (TEXES) imaging spectrometer at the NASA InfraRed Telescope Facility (IRTF, Mauna Kea Observatory). We present here the observations obtained between January 2016 and September 2018. As in the case of our previous runs, data were recorded around 1345 cm−1 (7.4 μm). The molecules SO2, CO2, and HDO (used as a proxy for H2O) were observed, and the cloudtop of Venus was probed at an altitude of about 64 km. The volume mixing ratio of SO2 was estimated using the SO2/CO2 line depth ratios of weak transitions; the H2O volume mixing ratio was derived from the HDO/CO2 line depth ratio, assuming a D/H ratio of 200 times the Vienna Standard Mean Ocean Water (VSMOW). As reported in our previous analyses, the SO2 mixing ratio shows strong variations with time and also over the disk, showing evidence of the formation of SO2 plumes with a lifetime of a few hours; in contrast, the H2O abundance is remarkably uniform over the disk and shows moderate variations as a function of time. We performed a statistical analysis of the behavior of the SO2 plumes, using all TEXES data between 2012 and 2018. They appear mostly located around the equator. Their distribution as a function of local time seems to show a depletion around noon; we do not have enough data to confirm this feature definitely. The distribution of SO2 plumes as a function of longitude shows no clear feature, apart from a possible depletion around 100E–150E and around 300E–360E. There seems to be a tendency for the H2O volume mixing ratio to decrease after 2016, and for the SO2 mixing ratio to increase after 2014. However, we see no clear anti-correlation between the SO2 and H2O abundances at the cloudtop, neither on the individual maps nor over the long term. Finally, there is a good agreement between the TEXES results and those obtained in the UV range (SPICAV/Venus Express and UVI/Akatsuki) at a slightly higher altitude. This agreement shows that SO2 observations obtained in the thermal infrared can be used to extend the local time coverage of the SO2 measurements obtained in the UV range.

Context. Planetary mass and radius data are showing a wide variety in densities of low-mass exoplanets. This includes sub-Neptunes, whose low densities can be explained with the presence of a volatile-rich layer. Water is one of the most abundant volatiles, which can be in the form of different phases depending on the planetary surface conditions. To constrain their composition and interior structure, it is required to develop models that calculate accurately the properties of water at its different phases. Aims. We present an interior structure model that includes a multiphase water layer with steam, supercritical and condensed phases. We derive the constraints for planetary compositional parameters and their uncertainties, focusing on the multiplanetary system TRAPPIST-1, which presents both warm and temperate planets. Methods. We use a 1D steam atmosphere in radiative-convective equilibrium with an interior whose water layer is in supercritical phase self-consistently. For temperate surface conditions, we implement liquid and ice Ih to ice VII phases in the hydrosphere. We adopt a MCMC inversion scheme to derive the probability distributions of core and water compositional parameters Results. We refine the composition of all planets and derive atmospheric parameters for planets b and c. The latter would be in a post-runaway greenhouse state and could be extended enough to be probed by space mission such as JWST. Planets d to h present condensed ice phases, with maximum water mass fractions below 20%. Conclusions. The derived amounts of water for TRAPPIST-1 planets show a general increase with semi-major axis, with the exception of planet d. This deviation from the trend could be due to formation mechanisms, such as migration and an enrichment of water in the region where planet d formed, or an extended CO$_{2}$-rich atmosphere., 11 pages, 7 figures. Accepted by Astronomy & Astrophysics (in press)

Based on the analysis of UV images (at 365 nm) of Venus cloud top (altitude 67 ± 2 km) collected with VMC (Venus Monitoring Camera) on board Venus Express (VEX), it is found that the zonal wind speed south of the equator (from 5°S to 15°S) shows a conspicuous variation (from -101 to -83 m/s) with geographic longitude of Venus, correlated with the underlying relief of Aphrodite Terra. We interpret this pattern as the result of stationary gravity waves produced at ground level by the up lift of air when the horizontal wind encounters a mountain slope. These waves can propagate up to the cloud top level, break there and transfer their momentum to the zonal flow. Such upward propagation of gravity waves and influence on the wind speed vertical profile was shown to play an important role in the middle atmosphere of the Earth by Lindzen [1981], but is not reproduced in the current GCM of Venus atmosphere from LMD. In the equatorial regions, the UV albedo at 365 nm varies also with longitude. We argue that this variation may be simply explained by the divergence of the horizontal wind field. In the longitude region (from 60° to -10°) where the horizontal wind speed is increasing in magnitude (stretch), it triggers air upwelling which brings the UV absorber at cloud top level and decreases the albedo, and vice-versa when the wind is decreasing in magnitude (compression). This picture is fully consistent with the classical view of Venus meridional circulation, with upwelling at equator revealed by horizontal air motions away from equator: the longitude effect is only an additional but important modulation of this effect. This interpretation is comforted by a recent map of cloud top H2O [Fedorova et al., 2015], showing that near the equator the lower UV albedo longitude region is correlated with increased H2O. We argue that H2O enhancement is the sign of upwelling, suggesting that the UV absorber is also brought to cloud top by upwelling.