Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

López‐Valverde, M. Á.; Gérard, Jean‐Claude; González‐Galindo, Francisco; Vandaele, Ann Carine; Thomas, Ian; Korablev, Oleg; Ignatiev, N.; Fedorova, Anna; Montmessin, Franck; Määttänen, Anni; Guilbon, Sabrina; Lefèvre, Franck; Patel, Manish R.; Jiménez-Monferrer, S.; García‐Comas, M.; Cardesin, Alejandro; Wilson, Colin; Clancy, R. T.; Kleinböhl, A.; McCleese, D. J.; Kass, D. M.; Schneider, N. M.; Chaffin, Michael; López-Moreno, J. J.; Rodriguez, J.

doi:10.1007/s11214-017-0463-4

Cited by 14 publications

(15 citation statements)

References 136 publications

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“…The full spectrum is always observed in limb observations and the integration time is kept at 20 s for the airglow observations. In this study, we use data collected by UVIS in the special limb modes where the UVIS channel usually pointing to nadir is oriented toward the planetary limb (López‐Valverde et al., 2018). They can either be “inertial” limb or “limb tracking” observations.…”

Section: Uvis Tgo Limb Observationsmentioning

confidence: 99%

The Mars Oxygen Visible Dayglow: A Martian Year of NOMAD/UVIS Observations

et al. 2022

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The Ultraviolet and Visible Spectrometer Ultraviolet (UVIS UV) and Visible Spectrometer channel of the Nadir and Occultation for MArs Discovery spectrometer aboard the ExoMars Trace Gas Orbiter has made limb observations of the Martian dayglow during more than a Martian year. Two pointing modes have been applied: (a) In the inertial mode, the spectrometer scans the atmosphere twice down to near the surface and provides altitude profiles of the dayglow; (b) in the tracking mode, the atmosphere is scanned at varying latitudes at a nearly constant altitude through the entire observation. We present a statistical study of the vertical and seasonal distribution of the recently discovered oxygen green and red lines at 557.7 nm and 630 nm. It indicates that the brightness of the green line emission responds to changes in the Lyman‐α flux. The peak altitude of the green line emission increases seasonally when the Sun‐Mars distance decreases. The lower peak of the green line statistically drops by 15–20 km between perihelion and aphelion at mid‐to high altitude. The main lower peak intensity shows an asymmetry between the two hemispheres. It is significantly brighter and more pronounced in the southern hemisphere than in the north. This is a consequence of the stronger Lyman‐α solar flux near perihelion. The second component of the oxygen red line at 636.4 nm is also detected for the first time in the Martian atmosphere. A photochemical model is used to simulate the variations of the green dayglow observed along limb tracking orbits.

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Section: Uvis Tgo Limb Observationsmentioning

confidence: 99%

The Mars Oxygen Visible Dayglow: A Martian Year of NOMAD/UVIS Observations

et al. 2022

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“…The UVIS‐NOMAD, an ultra‐light instrument covering the 200–650 nm spectral range, has both nadir and solar occultation modes. It has been occasionally operated to collect spectra in the “inertial limb” mode where the “nadir channel” points at the dayside limb in a fixed orientation in the inertial space (López‐Valverde et al., 2018). By virtue of the spacecraft's latitudinal motion along its orbit, the line of sight scans through the atmosphere from ∼400 km down to a predetermined altitude of the tangent point, generally close to 20 km.…”

Section: Limb Observations Of Oxygen Linesmentioning

confidence: 99%

“…In this study, we present new results related to the search for the presence of the nm emission in spectra obtained by averaging a large fraction of the dayside limb scans made with the UVIS instrument, which is part of the NOMAD suite of instruments (Patel et al, 2017;Vandaele et al, 2018) on board the TGO spacecraft. We determine its peak intensity and provide an estimate of its altitude distribution in the thermosphere.…”

Section: Introductionmentioning

confidence: 99%

First Observation of the Oxygen 630 nm Emission in the Martian Dayglow

Gérard

Aoki

Gkouvelis

et al. 2021

Geophysical Research Letters

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The first Martian dayglow observations were collected with the ultraviolet spectrometers on board Mariner 6, 7, and 9 flown to Mars in the early 1970s (Barth, 1974). They identified the presence of a series of oxygen and carbon lines and molecular bands originating from CO and CO 2 + . They obtained limb profiles of the strongest emissions. High quality extreme ultraviolet disk spectra were collected with the Hopkins Ultraviolet Telescope by Feldman et al. (2000). Later, limb observations with the SPICAM instrument on board Mars Express identified N 2 Vegard-Kaplan emissions in the middle ultraviolet (Leblanc et al., 2007). A major step forward was made with the Imaging Ultraviolet Spectrograph (IUVS) spectral imager on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, which has collected a wealth of ultraviolet limb scans (Jain et al., 2015).The possible presence of visible dayglow emissions in the Martian dayglow was investigated by Fox and Dalgarno (1979) who modeled the sources and sinks of O( 1 S) metastable atoms that produce emission of the green line and trans-auroral emissions at 555.7 and 297.2 nm respectively. They also predicted the

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“…The characteristics of UVIS are summarized in the Methods. As no airglow signal could be observed in the (limb) occultation channel, it was proposed 14 that the TGO spacecraft should be tilted to orient the line of sight of the nadir channel in the limb direction. This procedure was implemented as a test in April 2019.…”

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Detection of green line emission in the dayside atmosphere of Mars from NOMAD-TGO observations

et al. 2020

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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 1 . It is also observed as a thin layer of glow surrounding the Earth near 90 km altitude in the dayside atmosphere 2,3 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 CO 2 by solar Lyman α 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.The presence of the Martian green line dayglow emission was predicted about 40 years ago 4 . However, observations dedicated to the Martian dayglow have so far been sensitive to radiation beyond 340 nm, and thus focused on the ultraviolet (UV) spectrum [5][6][7][8] , including the Oi 297.2 nm emission. The [Oi] 557.7 and 297.2 nm forbidden emissions have the same 1 S upper state, so their intensity ratio is equal to that of their transition probability. The two transition probabilities and their ratio R = I(557.7 nm)/I(297.2 nm) have been obtained from ab initio calculations. The value recommended by NIST 1 is R = 16.7. However, atmospheric observations of the two emissions have led to lower values: R = 9.8 ± 1.0 in the terrestrial nightglow 9 and 9.3 ± 0.5 in the aurora 10 . These values depend on the instrumental calibration of two spectral windows bridged with the O 2 Herzberg i transition. As this ratio is invariant at low pressure, it is a useful standard for measurements connecting the UV and the visible regions.

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Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

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Cited by 14 publications

References 136 publications

The Mars Oxygen Visible Dayglow: A Martian Year of NOMAD/UVIS Observations

The Mars Oxygen Visible Dayglow: A Martian Year of NOMAD/UVIS Observations

First Observation of the Oxygen 630 nm Emission in the Martian Dayglow

Detection of green line emission in the dayside atmosphere of Mars from NOMAD-TGO observations

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