M. S. Chaffin, D. M. Kass, S. Aoki, A. A. Fedorova, J. Deighan, K. Connour, N. G. Heavens, A. Kleinböhl, S. K. Jain, J.-Y. Chaufray, M. Mayyasi, J. T. Clarke, A. I. F. Stewart, J. S. Evans, M. H. Stevens, W. E. McClintock, M. M. J. Crismani, G. M. Holsclaw, F. Lefevre, D. Y. Lo, F. Montmessin, N. M. Schneider, B. Jakosky, G. Villanueva, G. Liuzzi, F. Daerden, I. R. Thomas, J.-J. Lopez-Moreno, M. R. Patel, G. Bellucci, B. Ristic, J. T. Erwin, A. C. Vandaele, A. Trokhimovskiy, O. I. Korablev


Mars has lost most of its initial water to space as atomic hydrogen and oxygen. Spacecraft measurements have determined that present-day hydrogen escape undergoes large variations with season that are inconsistent with long-standing explanations. The cause is incompletely understood, with likely contributions from seasonal changes in atmospheric circulation, dust activity and solar extreme ultraviolet input. Although some modelling and indirect observational evidence suggest that dust activity can explain the seasonal trend, no previous study has been able to unambiguously distinguish seasonal from dust-driven forcing. Here we present synoptic measurements of dust, temperature, ice, water and hydrogen on Mars during a regional dust event, demonstrating that individual dust events can boost planetary H loss by a factor of five to ten. This regional storm occurred in the declining phase of the known seasonal trend, establishing that dust forcing can override this trend to drive enhanced escape. Because similar regional storms occur in most Mars years, these storms may be responsible for a large fraction of Martian water loss and represent an important driver of Mars atmospheric evolution.


chaffin et al



If you have interesting results that you would like to reach a wider audience, ESA can publicise your work!


Submission Procedure

  • This should be done around a month before the expected publishing date, e.g. when the first reviews come back after submission of your paper.
  • ESA will contact you, and assign a writer to develop your story, make infographics, etc.

Nature 568, 521–525 (2019)


Ann Carine Vandaele, Oleg Korablev, Frank Daerden, Shohei Aoki, Ian R. Thomas, Francesca Altieri, Miguel López-Valverde, Geronimo Villanueva, Giuliano Liuzzi, Michael D. Smith, Justin T. Erwin, Loïc Trompet, Anna A. Fedorova, Franck Montmessin, Alexander Trokhimovskiy, Denis A. Belyaev, Nikolay I. Ignatiev, Mikhail Luginin, Kevin S. Olsen, Lucio Baggio, Juan Alday, Jean-Loup Bertaux, Daria Betsis, David Bolsée, R. Todd Clancy, Edward Cloutis, Cédric Depiesse, Bernd Funke, Maia Garcia-Comas, Jean-Claude Gérard, Marco Giuranna, Francisco Gonzalez-Galindo, Alexey V. Grigoriev, Yuriy S. Ivanov, Jacek Kaminski, Ozgur Karatekin, Franck Lefèvre, Stephen Lewis, Manuel López-Puertas, Arnaud Mahieux, Igor Maslov, Jon Mason, Michael J. Mumma, Lori Neary, Eddy Neefs, Andrey Patrakeev, Dmitry Patsaev, Bojan Ristic, Séverine Robert, Frédéric Schmidt, Alexey Shakun, Nicholas A. Teanby, Sébastien Viscardy, Yannick Willame, James Whiteway, Valérie Wilquet, Michael J. Wolff, Giancarlo Bellucci, Manish R. Patel, Jose-Juan López-Moreno, François Forget, Colin F. Wilson, Håkan Svedhem, Jorge L. Vago, Daniel Rodionov, NOMAD Science Team & ACS Science Team


Global dust storms on Mars are rare but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere, primarily owing to solar heating of the dust. In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars. Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes, as well as a decrease in the water column at low latitudes. Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H2O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H2O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals. The observed changes in H2O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere.

S. Aoki, F. Daerden, S. Viscardy, I. R. Thomas, J. T. Erwin, S. Robert, L. Trompet, L. Neary, G. L. Villanueva, G. Liuzzi, M. M. J. Crismani, R. T. Clancy, J. Whiteway, F. Schmidt, M. A. Lopez-Valverde, B. Ristic, M. R. Patel, G. Bellucci, J.-J. Lopez-Moreno, K. S. Olsen, F. Lefèvre, F. Montmessin, A. Trokhimovskiy, A. A. Fedorova, O. Korablev, A. C. Vandaele


Hydrogen chloride (HCl) was recently discovered in the atmosphere of Mars by two spectrometers onboard the ExoMars Trace Gas Orbiter. The reported detection made in Martian Year 34 was transient, present several months after the global dust storm during the southern summer season. Here, we present the full data set of vertically resolved HCl detections obtained by the NOMAD instrument, which covers also Martian year 35. We show that the particular increase of HCl abundances in the southern summer season is annually repeated, and that the formation of HCl is independent from a global dust storm event. We also find that the vertical distribution of HCl is strikingly similar to that of water vapor, which suggests that the uptake by water ice clouds plays an important role. The observed rapid decrease of HCl abundances at the end of the southern summer would require a strong sink independent of photochemical loss.


aoki hcl h20

Nature 568, 517–520 (2019)


Oleg Korablev, Ann Carine Vandaele, Franck Montmessin, Anna A. Fedorova, Alexander Trokhimovskiy, François Forget, Franck Lefèvre, Frank Daerden, Ian R. Thomas, Loïc Trompet, Justin T. Erwin, Shohei Aoki, Séverine Robert, Lori Neary, Sébastien Viscardy, Alexey V. Grigoriev, Nikolay I. Ignatiev, Alexey Shakun, Andrey Patrakeev, Denis A. Belyaev, Jean-Loup Bertaux, Kevin S. Olsen, Lucio Baggio, Juan Alday, Yuriy S. Ivanov, Bojan Ristic, Jon Mason, Yannick Willame, Cédric Depiesse, Laszlo Hetey, Sophie Berkenbosch, Roland Clairquin, Claudio Queirolo, Bram Beeckman, Eddy Neefs, Manish R. Patel, Giancarlo Bellucci, Jose-Juan López-Moreno, Colin F. Wilson, Giuseppe Etiope, Lev Zelenyi, Håkan Svedhem, Jorge L. Vago & The ACS and NOMAD Science Teams


The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere, which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.


J.‐C. Gérard, S. Aoki, L. Gkouvelis, L. Soret, Y. Willame, I. R. Thomas, C. Depiesse, B. Ristic, A. C. Vandaele, B. Hubert, F. Daerden, M. R. Patel, J.‐J. López‐Moreno, G. Bellucci, J. P. Mason, M. A. López‐Valverde


Following the recent detection of the oxygen green line airglow on Mars, we have improved the statistical analysis of the data recorded by the NOMAD/UVIS instrument on board the ExoMars Trace Gas Orbiter mission by summing up hundreds of spectra to increase the signal‐to‐noise ratio. This led to the observation of the OI 630 nm emission, the first detection in a planetary atmosphere outside the Earth. The average limb profile shows a broad peak intensity of 4.8 kR near 150 km. Comparison with a photochemical model indicates that it is well predicted by current photochemistry, considering the sources of uncertainty. The red/green line intensity ratio decreases dramatically with altitude as a consequence of the efficient quenching of O(1D) by CO2. Simultaneous observations of the green and red dayglow will provide information on variations in the thermosphere in response to seasonal changes and the effects of solar events.


gerard 630nm emission



Icarus, Vol. 321, Issue 11, 670-691, DOI: 10.1016/j.icarus.2018.09.021. (2019)


Liuzzi, G.; Villanueva, G.L.; Mumma, M.J.; Smith, M.D.; Daerden, F.; Ristic, B.; Thomas, I.; Vandaele, A.C.; Patel, M.R.; Lopez-Moreno, J.-J.; Bellucci, G.


The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.

Giuliano Liuzzi, Geronimo L. Villanueva, Sebastien Viscardy, Daniel Mège, Matteo M. J. Crismani, Shohei Aoki, Joanna Gurgurewicz, Pierre‐Antoine Tesson, Michael J. Mumma, Michael D. Smith, Sara Faggi, Vincent Kofman, Elise W. Knutsen, Frank Daerden, Lori Neary, Frédéric Schmidt, Loïc Trompet, Justin T. Erwin, Séverine Robert, Ian R. Thomas, Bojan Ristic, Giancarlo Bellucci, Jóse Juan Lopez‐Moreno, Manish R. Patel, Ann Carine Vandaele
Following the recent detection of HCl in the atmosphere of Mars by ExoMars/Trace Gas Orbiter, we present here the first measurement of the 37Cl/35Cl isotopic ratio in the Martian atmosphere using a set of Nadir Occultation for MArs Discovery (NOMAD) observations. We determine an isotopic anomaly of −6 ± 78‰ compared to Earth standard, consistent with the −51‰–−1‰ measured on Mars’ surface by Curiosity. The measured isotopic ratio is also consistent with surface measurements, and suggests that Cl reservoirs may have undergone limited processing since formation in the Solar Nebula. The examination of possible sources and sinks of HCl shows only limited pathways to short‐term efficient Cl fractionation and many plausible reservoirs of “light” Cl.
liuzzi hcl isotope

Space Science Reviews, Vol. 214, Issue 5, A80, DOI: 10.1007/s11214-018-0517-2. (2018)


Vandaele, A.C.; Lopez-Moreno, J.-J.; Patel, M.R.; Bellucci, G.; Daerden, F.; Ristic, B.; Robert, S.; Thomas, I.R.; Wilquet, V.; Allen, M.; Alonso-Rodrigo, G.; Altieri, F.; Aoki, S.; Bolsée, D.; Clancy, T.; Cloutis, E.; Depiesse, C.; Drummond, R.; Fedorova, A.; Formisano, V.; Funke, B.; González-Galindo, F.; Geminale, A.; Gérard, J.-C.; Giuranna, M.; Hetey, L.; Ignatiev, N.; Kaminski, J.; Karatekin, O.; Kasaba, Y.; Leese, M.; Lefèvre, F.; Lewis, S.R.; López-Puertas, M.; López-Valverde, M.; Mahieux, A.; Mason, J.; McConnell, J.; Mumma, M.; Neary, L.; Neefs, E.; Renotte, E.; Rodriguez-Gomez, J.; Sindoni, G.; Smith, M.; Stiepen, A.; Trokhimovsky, A.; Vander Auwera, J.; Villanueva, G.; Viscardy, S.; Whiteway, J.; Willame, Y.; Wolff, M.; the NOMAD Team


The NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite on board the ExoMars Trace Gas Orbiter (TGO) has been designed to investigate the composition of Mars’ atmosphere, with a particular focus on trace gases, clouds and dust. The detection sensitivity for trace gases is considerably improved compared to previous Mars missions, compliant with the science objectives of the TGO mission. This will allow for a major leap in our knowledge and understanding of the Martian atmospheric composition and the related physical and chemical processes. The instrument is a combination of three spectrometers, covering a spectral range from the UV to the mid-IR, and can perform solar occultation, nadir and limb observations. In this paper, we present the science objectives of the instrument and explain the technical principles of the three spectrometers. We also discuss the expected performance of the instrument in terms of spatial and temporal coverage and detection sensitivity.


Michael D. Smith, Frank Daerden, Lori Neary, Alain S.J. Khayat, James A. Holmes, Manish R. Patel, Geronimo Villanueva, Giuliano Liuzzi, Ian R. Thomas, Bojan Ristic, Giancarlo Bellucci, Jose Juan Lopez-Moreno, Ann Carine Vandaele.


More than a full Martian year of observations have now been made by the Nadir Occultation for MArs Discovery (NOMAD) instrument suite on-board the ExoMars Trace Gas Orbiter. Radiative transfer modeling of NOMAD observations taken in the nadir geometry enable the seasonal and global-scale variations of carbon monoxide gas in the Martian atmosphere to be characterized. These retrievals show the column-averaged volume mixing ratio of carbon monoxide to be about 800 ppmv, with significant variations at high latitudes caused by the condensation and sublimation of the background CO2 gas. Near summer solstice in each hemisphere, the CO volume mixing ratio falls to 400 ppmv in the south and 600 ppmv in the north. At low latitudes, carbon monoxide volume mixing ratio inversely follows the annual cycle of surface pressure. Comparison of our retrieved CO volume mixing ratio against that computed by the GEM-Mars general circulation model reveals a good match in their respective seasonal and spatial trends, and can provide insight into the physical processes that control the distribution of CO gas in the current Martian atmosphere.


smith LNO CO

Space Sci Rev (2018) 214: 29.


Miguel A. López-Valverde, Jean-Claude Gerard, Francisco González-Galindo, Ann-Carine Vandaele, Ian Thomas, Oleg Korablev, Nikolai Ignatiev, Anna Fedorova, Franck Montmessin, Anni Määttänen, Sabrina Guilbon, Franck Lefevre, Manish R. Patel, Sergio Jiménez-Monferrer, Maya García-Comas, Alejandro Cardesin, Colin F. Wilson, R. T. Clancy, Armin Kleinböhl, Daniel J. McCleese, David M. Kass, Nick M. Schneider, Michael S. Chaffin, José Juan López-Moreno, Julio Rodríguez


The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere.

Space Science Reviews, 08 February 2021,

C. E. Newman, M. de la Torre Juárez, J. Pla-García, R. J. Wilson, S. R. Lewis, L. Neary, M. A. Kahre, F. Forget, A. Spiga, M. I. Richardson, F. Daerden, T. Bertrand, D. Viúdez-Moreiras, R. Sullivan, A. Sánchez-Lavega, B. Chide & J. A. Rodriguez-Manfredi

Nine simulations are used to predict the meteorology and aeolian activity of the Mars 2020 landing site region. Predicted seasonal variations of pressure and surface and atmospheric temperature generally agree. Minimum and maximum pressure is predicted at Ls∼145∘ and 250∘, respectively. Maximum and minimum surface and atmospheric temperature are predicted at Ls∼180∘ and 270∘, respectively; i.e., are warmest at northern fall equinox not summer solstice. Daily pressure cycles vary more between simulations, possibly due to differences in atmospheric dust distributions. Jezero crater sits inside and close to the NW rim of the huge Isidis basin, whose daytime upslope (∼east-southeasterly) and nighttime downslope (∼northwesterly) winds are predicted to dominate except around summer solstice, when the global circulation produces more southerly wind directions. Wind predictions vary hugely, with annual maximum speeds varying from 11 to 19 ms−1 and daily mean wind speeds peaking in the first half of summer for most simulations but in the second half of the year for two. Most simulations predict net annual sand transport toward the WNW, which is generally consistent with aeolian observations, and peak sand fluxes in the first half of summer, with the weakest fluxes around winter solstice due to opposition between the global circulation and daytime upslope winds. However, one simulation predicts transport toward the NW, while another predicts fluxes peaking later and transport toward the WSW. Vortex activity is predicted to peak in summer and dip around winter solstice, and to be greater than at InSight and much greater than in Gale crater.


 Icarus, Vol. 300, 458-476, DOI: 10.1016/j.icarus.2017.09.028. (2018)


Neary, L.; Daerden, F. 


GEM-Mars is a gridpoint-based three-dimensional general circulation model (GCM) of the Mars atmosphere extending from the surface to approximately 150 km based on the GEM (Global Environmental Multiscale) model, part of the operational weather forecasting and data assimilation system for Canada. After the initial modification for Mars, the model has undergone considerable changes. GEM-Mars is now based on GEM 4.2.0 and many physical parameterizations have been added for Mars-specific atmospheric processes and surface-atmosphere exchange. The model simulates interactive carbon dioxide-, dust-, water- and atmospheric chemistry cycles. Dust and water ice clouds are radiatively active. Size distributed dust is lifted by saltation and dust devils. The model includes 16 chemical species (CO2, Argon, N2, O2, CO, H2O, CH4, O3, O(1D), O, H, H2, OH, HO2, H2O2 and O2(a1g)) and has fully interactive photochemistry (15 reactions) and gas-phase chemistry (31 reactions). GEM-Mars provides a good simulation of the water and ozone cycles. A variety of other passive tracers can be included for dedicated studies, such as the emission of methane. The model has both a hydrostatic and non-hydrostatic formulation, and together with a flexible grid definition provides a single platform for simulations on a variety of horizontal scales. The model code is fully parallelized using OMP and MPI. Model results are evaluated by comparison to a selection of observations from instruments on the surface and in orbit, relating to atmosphere and surface temperature and pressure, dust and ice content, polar ice mass, polar argon, and global water and ozone vertical columns. GEM-Mars will play an integral part in the analysis and interpretation of data that is received by the NOMAD spectrometer on the ESA-Roskosmos ExoMars Trace Gas Orbiter. The present paper provides an overview of the current status and capabilities of the GEM-Mars model and lays the foundations for more in-depth studies in support of the NOMAD mission.

Science Advances 10 Feb 2021,

Geronimo L. Villanueva,Giuliano Liuzzi,Matteo M. J. Crismani,Shohei Aoki,Ann Carine Vandaele,Frank Daerden,Michael D. Smith, Michael J. Mumma,Elise W. Knutsen,Lori Neary,Sebastien Viscardy,Ian R. Thomas,Miguel Angel Lopez-Valverde,Bojan Ristic,Manish R. Patel,James A. Holmes,Giancarlo Bellucci,Jose Juan Lopez-Moreno, and the NOMAD team

Isotopic ratios and, in particular, the water D/H ratio are powerful tracers of the evolution and transport of water on Mars. From measurements performed with ExoMars/NOMAD, we observe marked and rapid variability of the D/H along altitude on Mars and across the whole planet. The observations (from April 2018 to April 2019) sample a broad range of events on Mars, including a global dust storm, the evolution of water released from the southern polar cap during southern summer, the equinox phases, and a short but intense regional dust storm. In three instances, we observe water at very high altitudes (>80 km), the prime region where water is photodissociated and starts its escape to space. Rayleigh distillation appears the be the driving force affecting the D/H in many cases, yet in some instances, the exchange of water reservoirs with distinctive D/H could be responsible.



Applied Optics, Vol. 56, Issue 10, 2771-2782 (2017), DOI: 10.1364/AO.56.002771.

Patel, M.R.; Antoine, P.; Mason, J.; Leese, M.; Hathi, B.; Stevens, A.H.; Dawson, D.; Gow, J.; Ringrose, T.; Holmes, J.; Lewis, S.R.; Beghuin, D.; Van Donink, P.; Ligot, R.; Dewandel, J.-L.; Hu, D.; Bates, D.; Cole, R.; Drummond, R.; Thomas, I.R.; Depiesse, C.; Neefs, E.; Equeter, E.; Ristic, B.; Berkenbosch, S.; Bolsée, D.; Willame, Y.; Vandaele, A.C.; Lesschaeve, S.; De Vos, L.; Van Vooren, N.; Thibert, T.; Mazy, E.; Rodriguez-Gomez, J.; Morales, R.; Candini, G.P.; Pastor-Morales, M.C.; Sanz, R.; Aparicio del Moral, B.; Jeronimo-Zafra, J.-M.; Gómez-López, J.M.; Alonso-Rodrigo, G.; Pérez-Grande, I.; Cubas, J.; Gomez-Sanjuan, A.M.; Navarro-Medina, F.; Benmoussa, A.; Giordanengo, B.; Gissot, S.; Bellucci, G.; Lopez-Moreno, J.J.

NOMAD is a spectrometer suite on board the ESA/Roscosmos ExoMars Trace Gas Orbiter, which launched in March 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel, allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at the day-and night-side, and during solar occultations. Here, in part 2 of a linked study, we describe the design, manufacturing, and testing of the ultraviolet and visible spectrometer channel called UVIS. We focus upon the optical design and working principle where two telescopes are coupled to a single grating spectrometer using a selector mechanism.

Science Advance 10 Feb 2021,

Oleg Korablev,Kevin S. Olsen,Alexander Trokhimovskiy,Franck Lefèvre,Franck Montmessin,Anna A. Fedorova,Michael J. Toplis,Juan Alday,Denis A. Belyaev,Andrey Patrakeev,Nikolay I. Ignatiev,Alexey V. Shakun,Alexey V. Grigoriev,Lucio Baggio,Irbah Abdenour,Gaetan Lacombe, Yury S. Ivanov,Shohei Aoki,Ian R. Thomas,Frank Daerden,Bojan Ristic,Justin T. Erwin,Manish Patel,Giancarlo Bellucci,Jose-Juan Lopez-Moreno, Ann C. Vandaele

A major quest in Mars’ exploration has been the hunt for atmospheric gases, potentially unveiling ongoing activity of geophysical or biological origin. Here, we report the first detection of a halogen gas, HCl, which could, in theory, originate from contemporary volcanic degassing or chlorine released from gas-solid reactions. Our detections made at ~3.2 to 3.8 μm with the Atmospheric Chemistry Suite and confirmed with Nadir and Occultation for Mars Discovery instruments onboard the ExoMars Trace Gas Orbiter, reveal widely distributed HCl in the 1- to 4-ppbv range, 20 times greater than previously reported upper limits. HCl increased during the 2018 global dust storm and declined soon after its end, pointing to the exchange between the dust and the atmosphere. Understanding the origin and variability of HCl shall constitute a major advance in our appraisal of martian geo- and photochemistry.



Space Telescopes and Instrumentation: Optical, Infrared, and Millimeter Wave, Proc. of SPIE Vol. 9904, 99045B (2016), doi:10.1117/12.2233353


Zafra, J.M.J.; Mesa, R.S.; López, J.M.G.; Gómez, J.F.R.; Del Moral, B.A.; Muñoz, R.M.; Candini, G.P.; Morales, M.C.P.; Muñoz, N.R.; López-Moreno, J.J.; Vandaele, A.C.; Neefs, E.; Drummond, R.; Delanoye, S.; Berkenbosch, S.; Clairquin, R.; Ristic, B.; Maes, J.; Bonnewijn, S.; Patel, M.R.; Leese, M.


NOMAD is a spectrometer suite: UV-visible-IR spectral ranges. NOMAD is part of the payload of ESA ExoMars Trace Gas Orbiter Mission. SINBAD boards are in charge of the communication and management of the power and control between the spacecraft and the instrument channels. SINBAD development took four years, while the entire development and test required five years, a very short time to develop an instrument devoted to a space mission. The hardware of SINBAD is shown in the attached poster: developed boards, prototype boards and final models. The models were delivered to the ESA in order to testing and integration with the spacecraft.

Icarus (2020)

Elise W. Knutsen, Geronimo L. Villanueva, Giuliano Liuzzi, Matteo M.J. Crismani, Michael J. Mumma, Michael D. Smith, Ann Carine Vandaele, Shohei Aoki, Ian R. Thomas, Frank Daerden, Sébastien Viscardy, Justin T. Erwin, Loic Trompet, Lori Neary, Bojan Ristic, Miguel Angel Lopez-Valverde, Jose Juan Lopez-Moreno, Manish R. Patel, Giancarlo Bellucci


Methane (CH4) on Mars has attracted a great deal of attention since it was first detected in January 2003. As methane is considered a potential marker for past/present biological or geological activity, any possible detection would require evidence with strong statistical significance. Ethane (C2H6) and ethylene (C2H4) are also relevant chemical species as their shorter lifetimes in the Martian atmosphere make them excellent tracers for recent and ongoing releases. If detected, a CH4/C2Hn ratio could aid in constraining the potential source of organic production. Here we present the results of an extensive search for hydrocarbons in the Martian atmosphere in 240,000 solar occultation measurements performed by the ExoMars Trace Gas Orbiter/NOMAD instrument from April 2018 to April 2019. The observations are global, covering all longitudes and latitudes from 85°N to 85°S, and sampled from 6 to 100 km altitude with a typical vertical resolution of 2 km. There were no statistically significant detections of organics and new stringent upper limits for global ethane and ethylene were set at 0.1 ppbv and 0.7 ppbv, respectively. No global background level of methane was observed, obtaining an upper limit of 0.06 ppbv, in agreement with early results from ExoMars (Korablev et al., 2019). Dedicated searches for localized plumes at more than 2000 locations provided no positive detections, implying that if methane were released in strong and rapid events, the process would have to be sporadic.


ch4 elise



Proceedings of SPIE 9904, Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, (2016) DOI: 10.1117/12.2230760.


Pastor-Morales, M.C.; Rodríguez-Gómez, J.F.; Morales-Muñoz, R.; Gómez-López, J.M.; Aparicio-del-Moral, B.; Candini, G.P.; Jerónimo-Zafra, J.M.; López-Moreno, J.J.; Robles-Muñoz, N.F.; Sanz-Mesa, R.; Neefs, E.; Vandaele, A.C.; Drummond, R.; Thomas, I.R.; Berkenbosch, S.; Clairquin, R.; Delanoye,S.; Ristic, B.; Maes, J.; Bonnewijn, S.; Patel, M.R.; Leese, M.; Mason, J.P.


The Spacecraft INterface and control Board for NomAD (SINBAD) is an electronic interface designed by the Instituto de Astrof´ısica de Andaluc´ıa (IAA-CSIC). It is part of the Nadir and Occultation for MArs Discovery instrument (NOMAD) on board in the ESA's ExoMars Trace Gas Orbiter mission. This mission was launched in March 2016. The SINBAD Flight Software (SFS) is the software embedded in SINBAD. It is in charge of managing the interfaces, devices, data, observing sequences, patching and contingencies of NOMAD. It is presented in this paper the most remarkable aspects of the SFS design, likewise the main problems and lessons learned during the software development process.



JQSRT (2021),

Frédéric Schmidt, Guillaume Cruz Mermy, Justin Erwin, Séverine Robert, Lori Neary, Ian R. Thomas, Frank Daerden, Bojan Ristic, Manish R. Patel, Giancarlo Bellucci, Jose-Juan Lopez-Moreno, Ann-Carine Vandaele


One of the main difficulties to analyze modern spectroscopic datasets is due to the large amount of data. For example, in atmospheric transmittance spectroscopy, the solar occultation channel (SO) of the NOMAD instrument onboard the ESA ExoMars2016 satellite called Trace Gas Orbiter (TGO) had produced ~ 10 millions of spectra in ~ 20000 acquisition sequences since the beginning of the mission in April 2018 until 15 January 2020. Other datasets are even larger with ~ billions of spectra for OMEGA onboard Mars Express or CRISM onboard Mars Reconnaissance Orbiter. Usually, new lines are discovered after a long iterative process of model fitting and manual residual analysis. Here we propose a new method based on unsupervised machine learning, to automatically detect new minor species. Although precise quantification is out of scope, this tool can also be used to quickly summarize the dataset, by giving few endmembers (”source”) and their abundances.

The methodology is the following: we proposed a way to approximate the dataset non-linearity by a linear mixture of abundance and source spectra (endmembers). We used unsupervised source separation in form of non-negative matrix factorization to estimate those quantities. Several methods are tested on synthetic and simulation data. Our approach is dedicated to detect minor species spectra rather than precisely quantifying them. On synthetic example, this approach is able to detect chemical compounds present in form of 100 hidden spectra out of 104, at 1.5 times the noise level. Results on simulated spectra of NOMAD-SO targeting CH4 show that detection limits goes in the range of 100–500 ppt in favorable conditions. Results on real martian data from NOMAD-SO show that CO2 and H2O are present, as expected, but CH4 is absent. Nevertheless, we confirm a set of new unexpected lines in the database, attributed by ACS instrument Team to the CO2 magnetic dipole.

[Ian: This paper concerns VEx/SOIR, but is included here on the NOMAD website because the same algorithm is used to calibrate SO and UVIS occultations]


Applied Optics (2016) Vol. 55, Issue 32, pp. 9275 - 9281

Loic Trompet, Arnaud Mahieux, Bojan Ristic, Séverine Robert, Valérie Wilquet, Ian R. Thomas, Ann Carine Vandaele, and Jean-Loup Bertaux


The Solar Occultation in the InfraRed (SOIR) instrument onboard the ESA Venus Express spacecraft, an infrared spectrometer sensitive from 2.2 to 4.3 μm, probed the atmosphere of Venus from June 2006 until December 2014. During this time, it performed more than 750 solar occultations of the Venus mesosphere and lower thermosphere. A new procedure has been developed for the estimation of the transmittance in order to decrease the number of rejected spectra, to check that the treated spectra are well calibrated, and to improve the quality of the calibrated spectra by reducing the noise and accurately normalizing it to the solar spectrum.

Nature Astronomy (2020),,


Gérard, J.-C.,; Aoki, S.; Willame, Y.; Gkouvelis, L.; Depiesse, C.; Thomas, I.R. | Ristic, B.; Vandaele, A.C.; Daerden, F.; Hubert, B.; Mason, J.; Patel, M.R.; López-Moreno, J.-J.; Bellucci, G.; López-Valverde, M.A.; Beeckman, B. 


The oxygen emission at 557.7 nm is a ubiquitous component of the spectrum of the terrestrial polar aurora and the reason for its usual green colour. It is also observed as a thin layer of glow surrounding the Earth near 90 km altitude in the dayside atmosphere but it has so far eluded detection in other planets. Here we report dayglow observations of the green line outside the Earth. They have been performed with the Nadir and Occultation for MArs Discovery ultraviolet and visible spectrometer instrument on board the European Space Agency’s ExoMars Trace Gas Orbiter. Using a special observation mode, scans of the dayside limb provide the altitude distribution of the intensity of the 557.7 nm line and its variability. Two intensity peaks are observed near 80 and 120 km altitude, corresponding to photodissociation of CO2 by solar Lyman alpha and extreme ultraviolet radiation, respectively. A weaker emission, originating from the same upper level of the oxygen atom, is observed in the near ultraviolet at 297.2 nm.These simultaneous measurements of both oxygen lines make it possible to directly derive a ratio of 16.5 between the visible and ultraviolet emissions, and thereby clarify a controversy between discordant ab initio calculations and atmospheric measurements that has persisted despite multiple efforts.This ratio is considered a standard for measurements connecting the ultraviolet and visible spectral regions. This result has consequences for the study of auroral and airglow processes and for spectral calibration.


green line

 Planetary and Space Science, (2016), Vol. 124, 94-104, DOI: 10.1016/j.pss.2016.03.003.


Robert, S.; Vandaele, A.C.; Thomas, I.; Willame, Y.; Daerden, F.; Delanoye, S.; Depiesse, C.; Drummond, R.; Neefs, E.; Neary, L.; Ristic, B.; Mason, J.; Lopez-Moreno, J.-J.; Rodriguez-Gomez, J.; Patel, M.R.; Bellucci, G.; the NOMAD Team


NOMAD (Nadir and Occultation for MArs Discovery) is one of the four instruments on board the ExoMars Trace Gas Orbiter, scheduled for launch in March 2016. It consists of a suite of three high-resolution spectrometers – SO (Solar Occultation), LNO (Limb, Nadir and Occultation) and UVIS (Ultraviolet and Visible Spectrometer). Based upon the characteristics of the channels and the values of Signal-to-Noise Ratio obtained from radiometric models discussed in (Vandaele et al., 2015a and Vandaele et al., 2015b; Thomas et al., 2016), the expected performances of the instrument in terms of sensitivity to detection have been investigated. The analysis led to the determination of detection limits for 18 molecules, namely CO, H2O, HDO, C2H2, C2H4, C2H6, H2CO, CH4, SO2, H2S, HCl, HCN, HO2, NH3, N2O, NO2, OCS, O3. NOMAD should have the ability to measure methane concentrations <25 parts per trillion (ppt) in solar occultation mode, and 11 parts per billion in nadir mode. Occultation detections as low as 10 ppt could be made if spectra are averaged (Drummond et al., 2011). Results have been obtained for all three channels in nadir and in solar occultation.

JGR (2020),


Liuzzi, G.; Villanueva, G.L.; Crismani, M.M.J.; Smith, M.D.; Mumma, M.J.; Daerden, F.; Aoki, S.; Vandaele, A.C.; Clancy, R.T.; Erwin, J.; Thomas, I.; Ristic, B.; Lopez-Moreno, J.-J.; Bellucci, G.; Patel, M.R.


Observations of water ice clouds and aerosols on Mars can provide important insights into the complexity of the water cycle. Recent observations have indicated an important link between dust activity and the water cycle, as intense dust activity can significantly raise the hygropause, and subsequently increase the escape of water after dissociation in the upper atmosphere. Here present observations from Nadir and Occultation for MArs Discovery/Trace Gas Orbiter that investigate the variation of water ice clouds in the perihelion season of Mars year 34 (April 2018–2019), their diurnal and seasonal behavior, and the vertical structure and microphysical properties of water ice and dust. These observations reveal the recurrent presence of a layer of mesospheric water ice clouds subsequent to the 2018 global dust storm. We show that this layer rose from 45 to 80 km in altitude on a time scale of days from heating in the lower atmosphere due to the storm. In addition, we demonstrate that there is a strong dawn‐dusk asymmetry in water ice abundance, related to nighttime nucleation and subsequent daytime sublimation. Water ice particle sizes are retrieved consistently and exhibit sharp vertical gradients (from 0.1 to 4.0 μm), as well as mesospheric differences between the global dust storm (<0.5 μm) and the 2019 regional dust storm (1.0 μm), which suggests differing water ice nucleation efficiencies. These results form the basis to advance our understanding of mesospheric water ice clouds on Mars, and further constrain the interactions between water ice and dust in the middle atmosphere.


Figure 05

Optics Express, Vol. 24, Issue 4, 3790-3805 (2016), DOI: 10.1364/OE.24.003790.


Thomas, I.R.; Vandaele, A.-C.; Robert, S.; Neefs, E.; Drummond, R.; Daerden, F.; Delanoye, S.; Ristic, B.; Berkenbosch, S.; Clairquin, R.; Maes, J.; Bonnewijn, S.; Depiesse, C.; Mahieux, A.; Trompet, L.; Neary, L.; Willame, Y.; Wilquet, V.; Nevejans, D.; Aballea, L.; Moelans, W.; De Vos, L.; Lesschaeve, S.; Van Vooren, N.; Lopez-Moreno, J.J.; Patel, M.R.; Bellucci, G.; the NOMAD Team


NOMAD is a suite of three spectrometers that will be launched in 2016 as part of the joint ESA-Roscosmos ExoMars Trace Gas Orbiter mission. The instrument contains three channels that cover the IR and UV spectral ranges and can perform solar occultation, nadir and limb observations, to detect and map a wide variety of Martian atmospheric gases and trace species. Part I of this work described the models of the UVIS channel; in this second part, we present the optical models representing the two IR channels, SO (Solar Occultation) and LNO (Limb, Nadir and Occultation), and use them to determine signal to noise ratios (SNRs) for many expected observational cases. In solar occultation mode, both the SO and LNO channel exhibit very high SNRs >5000. SNRs of around 100 were found for the LNO channel in nadir mode, depending on the atmospheric conditions, Martian surface properties, and observation geometry.

Icarus (2020),


A. Cardesin-Moinelo, B. Geiger, G. Lacombe, B. Ristic, M. Costa, D. Titov, H. Svedhem, J. Marin-Yaseli, D. Merritt, P. Martin, M.A. Lopez-Valverde


Two spacecraft launched and operated by the European Space Agency are currently performing observations in Mars orbit. For >15 years Mars Express has been conducting global surveys of the surface, the atmosphere and the plasma environment of the Red Planet. The Trace Gas Orbiter, the first element of the ExoMars programme, began its science phase in 2018 focusing on investigations of the atmospheric composition with unprecedented sensitivity as well as surface and subsurface studies. The coordination of observation programmes of both spacecraft aims at cross calibration of the instruments and exploitation of new opportunities provided by the presence of two spacecraft whose science operations are performed by two closely collaborating teams at the European Space Astronomy Centre (ESAC). 

 alex joint ops

Optical and radiometric models of the NOMAD instrument part I: the UVIS channel. , Optics Express (2015), Vol. 23, Issue 23, 30028-30042, DOI: 10.1364/OE.23.030028.


Vandaele, A.C.; Willame, Y.; Depiesse, C.; Thomas, I.R.; Robert, S.; Bolsee, D.; Patel, M.R.; Mason, J.P.; Leese, M.; Lesschaeve, S.; Antoine, P.; Daerden, F.; Delanoye, S.; Drummond, R.; Neefs, E.; Ristic, B.; Lopez-Moreno, J.J.; Bellucci, G.; the NOMAD Team 


The NOMAD instrument has been designed to best fulfil the science objectives of the ExoMars Trace Gas Orbiter mission that will be launched in 2016. The instrument is a combination of three channels that cover the UV, visible and IR spectral ranges and can perform solar occultation, nadir and limb observations. In this series of two papers, we present the optical models representing the three channels of the instrument and use them to determine signal to noise levels for different observation modes and Martian conditions. In this first part, we focus on the UVIS channel, which will sound the Martian atmosphere using nadir and solar occultation viewing modes, covering the 200-650nm spectral range. High SNR levels (>1000) can easily be reached for wavelengths higher than 300nm both in solar occultation and nadir modes when considering binning. Below 300nm SNR are lower primarily because of the lower signal and the impact of atmospheric absorption.

JGR (2019)


Aoki, S.; Vandaele, A.C.; Daerden, F.; Villanueva, G.L.; Liuzzi, G.; Thomas, I.R.; Erwin, J.T.; Trompet, L.; Robert, S.; Neary, L.; Viscardy, S.; Clancy, R.T.; Smith, M.D.; Lopez‐Valverde, M.A.; Hill, B.; Ristic, B.; Patel, M.R.; Bellucci, G.; Lopez‐Moreno, J.-J.; the NOMAD team


It has been suggested that dust storms efficiently transport water vapor from the near‐surface to the middle atmosphere on Mars. Knowledge of the water vapor vertical profile during dust storms is important to understand water escape. During Martian Year 34, two dust storms occurred on Mars: a global dust storm (June to mid‐September 2018) and a regional storm (January 2019). Here we present water vapor vertical profiles in the periods of the two dust storms (Ls = 162–260° and Ls = 298–345°) from the solar occultation measurements by Nadir and Occultation for Mars Discovery (NOMAD) onboard ExoMars Trace Gas Orbiter (TGO). We show a significant increase of water vapor abundance in the middle atmosphere (40–100 km) during the global dust storm. The water enhancement rapidly occurs following the onset of the storm (Ls~190°) and has a peak at the most active period (Ls~200°). Water vapor reaches very high altitudes (up to 100 km) with a volume mixing ratio of ~50 ppm. The water vapor abundance in the middle atmosphere shows high values consistently at 60°S‐60°N at the growth phase of the dust storm (Ls = 195°–220°), and peaks at latitudes greater than 60°S at the decay phase (Ls = 220°–260°). This is explained by the seasonal change of meridional circulation: from equinoctial Hadley circulation (two cells) to the solstitial one (a single pole‐to‐pole cell). We also find a conspicuous increase of water vapor density in the middle atmosphere at the period of the regional dust storm (Ls = 322–327°), in particular at latitudes greater than 60°S.


water shohei

Planetary and Space Science (2015), Vol. 119, 233, DOI: 10.1016/j.pss.2015.10.003.


Vandaele A. C.; Neefs E.; Drummond R.; Thomas I. R.; Daerden F.; Lopez-Moreno J.-J.; Rodriguez J.; Patel M. R.; Bellucci G.; Allen M.; Altieri F.; Bolsée D.; Clancy T.; Delanoye S.; Depiesse C.; Cloutis E.; Fedorova A.; Formisano V.; Funke B.; Fussen D.; Geminale A.; Gérard J.-C.; Giuranna M.; Ignatiev N.; Kaminski J.; Karatekin O.; Lefèvre F.; López-Puertas M.; López-Valverde M.; Mahieux A.; McConnell J.; Mumma M.; Neary L.; Renotte E.; Ristic B.; Robert S.; Smith M.; Trokhimovsky S.; Vander Auwera J.; Villanueva G.; Whiteway J.; Wilquet V.; Wolff M. 


The NOMAD spectrometer suite on the ExoMars Trace Gas Orbiter will map the composition and distribution of Mars׳ atmospheric trace species in unprecedented detail, fulfilling many of the scientific objectives of the joint ESA-Roscosmos ExoMars Trace Gas Orbiter mission. The instrument is a combination of three channels, covering a spectral range from the UV to the IR, and can perform solar occultation, nadir and limb observations. In this paper, we present the science objectives of the instrument and how these objectives have influenced the design of the channels. We also discuss the expected performance of the instrument in terms of coverage and detection sensitivity.

Aircraft Engineering and Aerospace Technology (2019),


Laszlo Hetey, Eddy Neefs, Ian Thomas, Joe Zender, Ann-Carine Vandaele, Sophie Berkenbosch, Bojan Ristic, Sabrina Bonnewijn, Sofie Delanoye, Mark Leese, Jon Mason, Manish Patel


This paper aims to describe the development of a knowledge management system (KMS) for the Nadir and Occultation for Mars Discovery (NOMAD) instrument on board the ESA/Roscosmos 2016 ExoMars Trace Gas Orbiter (TGO) spacecraft. The KMS collects knowledge acquired during the engineering process that involved over 30 project partners. In addition to the documentation and technical data (explicit knowledge), a dedicated effort was made to collect the gained experience (tacit knowledge) that is crucial for the operational phase of the TGO mission and also for future projects. The system is now in service and provides valuable information for the scientists and engineers working with NOMAD.

Applied Optics, Vol. 54, Issue 28, 8494-8520, DOI: 10.1364/AO.54.008494. 


Neefs, E.; Vandaele, A.C.; Drummond, R.; Thomas, I.R.; Berkenbosch, S.; Clairquin, R.; Delanoye, S.; Ristic, B.; Maes, J.; Bonnewijn, S.; Pieck, G.; Equeter, E.; Depiesse, C.; Daerden, F.; Van Ransbeeck, E.; Nevejans, D.; Rodriguez-Gomez, J.; Lopez-Moreno, J.-J.; Sanz, R.; Morales, R.; Candini, G.P.; Pastor-Morales, M.C.; Del Moral, B.A.; Jeronimo-Zafra, J.-M.; Gomez-Lopez, J.M.; Alonso-Rodrigo, G.; Perez-Grande, I.; Cubas, J.; Gomez-Sanjuan, A.M.; Navarro-Medina, F.; Thibert, T.; Patel, M.R.; Bellucci, G.; De Vos, L.; Lesschaeve, S.; Van Vooren, N.; Moelans, W.; Aballea, L.; Glorieux, S.; Baeke, A.; Kendall, D.; De Neef, J.; Soenen, A.; Puech, P.-Y.; Ward, J.; Jamoye, J.-F.; Diez, D.; Vicario-Arroyo, A.; Jankowski, M.


NOMAD is a spectrometer suite on board ESA’s ExoMars trace gas orbiter due for launch in January 2016. NOMAD consists of two infrared channels and one ultraviolet and visible channel allowing the instrument to perform observations quasi-constantly, by taking nadir measurements at dayside and nightside, and during solar occultations. In this paper, the design, manufacturing, and testing of the two infrared channels are described. We focus upon the optical working principle in these channels, where an echelle grating, used as a diffractive element, is combined with an acousto-optical tunable filter, used as a diffraction order sorter.

Icarus (2019),

L. Neary, F. Daerden, S. Aoki, J. Whiteway, R. T. Clancy, M. Smith, S. Viscardy, J. T. Erwin, I. R. Thomas, G. Villanueva, G. Liuzzi, M. Crismani, M. Wolff, S. R. Lewis, J. A. Holmes, M. R. Patel, M. Giuranna, C. Depiesse, A. Piccialli, S. Robert, L. Trompet, Y. Willame, B. Ristic, A. C. Vandaele


The Nadir and Occultation for MArs Discovery (NOMAD) instrument on board ExoMars Trace Gas Orbiter (TGO) measured a large increase in water vapor at altitudes in the range of 40-100 km during the 2018 global dust storm on Mars. Using a three-dimensional general circulation model, we examine the mechanism responsible for the enhancement of water vapor in the upper atmosphere. Experiments with different prescribed vertical profiles of dust show that when more dust is present higher in the atmosphere the temperature increases and the amount of water ascending over the tropics is not limited by saturation until reaching heights of 70-100 km. The warmer temperatures allow more water to ascend to the mesosphere. Photochemical simulations show a strong increase in high-altitude atomic hydrogen following the high-altitude water vapor increase by a few days.