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Reflectivity of Venusâs Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives
We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52â1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283â800 nm wavelengths. Considerable absorption is present in the 350â450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns
Etude de lâexosphĂšre de Mercure par le spectromĂštre PHEBUS de la mission BepiColombo
Mercury is the least explored of the inner planets, only three spacecraft have explored it. Mariner 10 observed the planet during three close encounters in 1974 and 1975, unveiling a very thin atmosphere surrounding the planet, somewhat similar to that of the Moon, including hydrogen (H) and helium (He). Sodium (Na), potassium (K) and calcium (Ca) were later detected in Mercuryâs exosphere with ground based telescopes. The MESSENGER mission, launched in 2004, not only performed three close encounters of the planet but also orbited it for four years. The mission added magnesium (Mg) and manganese (Mn) to the list of species detected in Mercuryâs exosphere. Iron (Fe) and aluminum (Al) were also discovered from ground-based observations around the same period.BepiColombo is the third mission to visit Mercury. Launched in 2018, the ESA-JAXA joint mission is set to perform six flybys of Mercury before the insertion in orbit around the planet at the end of 2025. Three flybys of Mercury have already been performed, during which PHEBUS (Probing the Hermean Exosphere By Ultraviolet Spectroscopy) was able to observe the surfacebounded exosphere of Mercury. The instrument consists of two UV detectors (EUV and FUV) and two visible channels (c404 and c422). The c404 channel is dedicated to the K emission line at 404.7 nm while the c422 channel is dedicated to the Ca emission line at 422.8 nm. The geometry of observation was similar during the first two flybys, the spacecraft approaching the planet from its nightside, crossing its shadow before moving to its dayside. The closest approach to the surface occurred in the shadow of Mercury at an altitude of âŒ200 km. PHEBUS was pointing northward, slightly antisunward.The count rate registered by both channels depicts the geometry of observation, notably the transit in the shadow of Mercury. The maximum is reached shortly after the spacecraft went out of eclipse. The count rate then decreases as the spacecraft moved away from Mercury. During the flybys, both signals are polluted by sporadic spikes whose origin remains uncertain.Despite these spikes, Ca was clearly detected by the c422 channel. The c422 signal shows not only an enhancement of Ca at dawn but also a very extensive Ca corona on the morning side, which was not reported by MESSENGER. The scale height deduced from our Ca profiles (2,500â2,800 km) is in agreement with the value reported by MESSENGER at similar true anomaly angle. Using the Chamberlain model, I determined a high temperature at the exobase (>50,000 K), in agreement with MESSENGER results. Both the large scale height and temperature at the exobase imply a very energetic release process. I also report a day/night asymmetry in the Ca exosphere that could indicate that the source of Ca is predominantly on the dayside or be the consequence of a shift of the main source of Ca away from the dawn region. The next step consists in using a 3D exospheric model that will include the effects of photoionization and non uniform distribution of Ca. Finally, PHEBUS pointing during the flybys did not allow to observe the potential cold component of Ca as the altitudes 50 000K), ce qui est en accord avec les rĂ©sultats de MESSENGER. La grande hauteur dâĂ©chelle et la tempĂ©rature Ă lâexobase Ă©levĂ©e impliquent un processus de libĂ©ration trĂšs Ă©nergĂ©tique. Les donnĂ©es semblent Ă©galement indiquer une asymĂ©trie jour/nuit qui pourrait signifier que la source de Ca est principalement du cĂŽtĂ© jour ou ĂȘtre la consĂ©quence dâun dĂ©calage de la source de Ca par rapport Ă la rĂ©gion de lâaube. La prochaine Ă©tape consiste Ă utiliser un modĂšle exosphĂ©rique 3D prenant en compte la photoionisation et la distribution non uniforme du Ca. Enfin, le pointage de PHEBUS lors de ces deux premiers survols nâa pas permis dâobserver la potentielle composante froide du Ca puisque les altitudes <200 km nâont pas Ă©tĂ© explorĂ©es.Le canal c404 a dĂ©tectĂ© une ou plusieurs espĂšces Ă basse altitude cĂŽtĂ© matin lors des survols, potentiellement du K ou du Mn. Cette ligne dâĂ©mission du K nâa jamais Ă©tĂ© dĂ©tectĂ©e par MESSENGER.Quant au Mn, MESSENGER ne lâa pas observĂ© continuellement, il nâa Ă©tĂ© dĂ©tectĂ© quâĂ certaines saisons et dans certaines rĂ©gions de lâexosphĂšre.Ces conditions de dĂ©tection sont bien diffĂ©rentes de celles de BepiColombo.Il est donc difficile dâidentifier avec certitude lâespĂšce dĂ©tectĂ©e. Dâautres observations sont nĂ©cessaires.On peut tout de mĂȘme mentionner que lâĂ©chelle de hauteur dĂ©duite du profil c404 est âŒ135 km et que le modĂšle de Chamberlain appliquĂ© au profil c404 semble indiquer une tempĂ©rature Ă lâexobase <3000 K
Etude de lâexosphĂšre de Mercure par le spectromĂštre PHEBUS de la mission BepiColombo
Mercure est la planĂšte tellurique la moins explorĂ©e du systĂšme solaire, trois missions seulement lâont survolĂ©e. Mariner 10 a effectuĂ© trois survols de la planĂšte en 1974 et 1975, dĂ©couvrant une atmosphĂšre trĂšs mince, similaire Ă celle de la Lune, contenant de lâhĂ©lium (He) et de lâhydrogĂšne (H). Le sodium (Na), le potassium (K) et le calcium (Ca) ont Ă©tĂ© dĂ©tectĂ©s plus tard Ă partir dâobservations depuis la Terre. La mission MESSENGER, lancĂ©e en 2004, a non seulement survolĂ© Mercure Ă trois reprises mais a Ă©galement orbitĂ© la planĂšte durant quatre ans. Elle a dĂ©tectĂ© deux nouvelles espĂšces, le magnĂ©sium (Mg) et le manganĂšse (Mn). En parallĂšle, deux autres espĂšces ont Ă©tĂ© dĂ©couvertes grĂące Ă des observations depuis la Terre : le fer (Fe) et lâaluminium (Al). BepiColombo est la troisiĂšme mission Ă destination de Mercure. LancĂ©e en 2018, la mission conjointe ESA JAXA doit effectuer six survols de Mercure avant de sâinsĂ©rer en orbite fin 2025. Trois survols de Mercure ont dĂ©jĂ Ă©tĂ© rĂ©alisĂ©s lors desquels PHEBUS (Probing the Hermean Exosphere By Ultraviolet Spectroscopy) a pu observer lâexosphĂšre de Mercure. Lâinstrument est composĂ© de deux dĂ©tecteurs UV (EUV et FUV) et de deux canaux visibles (c404 et c422). Le canal c404 est dĂ©diĂ© Ă la ligne dâĂ©mission du K Ă 404,7 nm tandis que le canal c422 est dĂ©diĂ© Ă la ligne dâĂ©mission du Ca Ă 422,8 nm. La gĂ©omĂ©trie dâobservation des deux premiers survols est similaire, la sonde approchant la planĂšte cĂŽtĂ© nuit, traversant son ombre avant de se diriger cĂŽtĂ© jour. La sonde sâest approchĂ©e Ă âŒ200 km de la surface au point le plus proche cĂŽtĂ© nuit. PHEBUS pointait vers le nord, dans une direction opposĂ©e au soleil. Le taux de comptage enregistrĂ© par les deux canaux visibles illustre la gĂ©omĂ©trie dâobservation, notamment le passage dans lâombre de Mercure. Le maximum est atteint peu aprĂšs la sortie dâĂ©clipse. Le taux de comptage diminue ensuite Ă mesure que la sonde sâĂ©loigne de Mercure. Lors des survols, les signaux des deux canaux sont polluĂ©s par des pics sporadiques dont lâorigine reste incertaine. MalgrĂ© ces pics, le canal c422 a clairement dĂ©tectĂ© du Ca. Le signal c422 montre non seulement une concentration de Ca Ă lâaube mais Ă©galement une couronne de Ca trĂšs Ă©tendue du cĂŽtĂ© matin qui nâa pas Ă©tĂ© rapportĂ©e par MESSENGER. La hauteur dâĂ©chelle dĂ©duite de nos profils (2500-2800 km) est en accord avec la valeur rapportĂ©e par MESSENGER Ă un angle dâanomalie vraie similaire. En utilisant le modĂšle de Chamberlain, jâai dĂ©terminĂ© une tempĂ©rature Ă lâexobase trĂšs Ă©levĂ©e (>50 000K), ce qui est en accord avec les rĂ©sultats de MESSENGER. La grande hauteur dâĂ©chelle et la tempĂ©rature Ă lâexobase Ă©levĂ©e impliquent un processus de libĂ©ration trĂšs Ă©nergĂ©tique. Les donnĂ©es semblent Ă©galement indiquer une asymĂ©trie jour/nuit qui pourrait signifier que la source de Ca est principalement du cĂŽtĂ© jour ou ĂȘtre la consĂ©quence dâun dĂ©calage de la source de Ca par rapport Ă la rĂ©gion de lâaube. La prochaine Ă©tape consiste Ă utiliser un modĂšle exosphĂ©rique 3D prenant en compte la photoionisation et la distribution non uniforme du Ca. Enfin, le pointage de PHEBUS lors de ces deux premiers survols nâa pas permis dâobserver la potentielle composante froide du Ca puisque les altitudes 50,000 K), in agreement with MESSENGER results. Both the large scale height and temperature at the exobase imply a very energetic release process. I also report a day/night asymmetry in the Ca exosphere that could indicate that the source of Ca is predominantly on the dayside or be the consequence of a shift of the main source of Ca away from the dawn region. The next step consists in using a 3D exospheric model that will include the effects of photoionization and non uniform distribution of Ca. Finally, PHEBUS pointing during the flybys did not allow to observe the potential cold component of Ca as the altitudes <200 km were not explored.The c404 channel detected species at low altitudes on the morning side during the flybys, potentially K or Mn. This K emission line was never detected by MESSENGER. As for Mn, MESSENGER has not observed it continuously, its detection was confined to certain seasons and to certain regions of the exosphere. These detection conditions are very different from those of BepiColombo. It is therefore difficult to identify with certainty the detected species. Further observations are necessary. Note that the scale height deduced from the c404 profile is âŒ135 km and that the Chamberlain model applied to the c404 profile seems to indicate a temperature at the exobase <3000 K
Etude de lâexosphĂšre de Mercure par le spectromĂštre PHEBUS de la mission BepiColombo
Mercury is the least explored of the inner planets, only three spacecraft have explored it. Mariner 10 observed the planet during three close encounters in 1974 and 1975, unveiling a very thin atmosphere surrounding the planet, somewhat similar to that of the Moon, including hydrogen (H) and helium (He). Sodium (Na), potassium (K) and calcium (Ca) were later detected in Mercuryâs exosphere with ground based telescopes. The MESSENGER mission, launched in 2004, not only performed three close encounters of the planet but also orbited it for four years. The mission added magnesium (Mg) and manganese (Mn) to the list of species detected in Mercuryâs exosphere. Iron (Fe) and aluminum (Al) were also discovered from ground-based observations around the same period.BepiColombo is the third mission to visit Mercury. Launched in 2018, the ESA-JAXA joint mission is set to perform six flybys of Mercury before the insertion in orbit around the planet at the end of 2025. Three flybys of Mercury have already been performed, during which PHEBUS (Probing the Hermean Exosphere By Ultraviolet Spectroscopy) was able to observe the surfacebounded exosphere of Mercury. The instrument consists of two UV detectors (EUV and FUV) and two visible channels (c404 and c422). The c404 channel is dedicated to the K emission line at 404.7 nm while the c422 channel is dedicated to the Ca emission line at 422.8 nm. The geometry of observation was similar during the first two flybys, the spacecraft approaching the planet from its nightside, crossing its shadow before moving to its dayside. The closest approach to the surface occurred in the shadow of Mercury at an altitude of âŒ200 km. PHEBUS was pointing northward, slightly antisunward.The count rate registered by both channels depicts the geometry of observation, notably the transit in the shadow of Mercury. The maximum is reached shortly after the spacecraft went out of eclipse. The count rate then decreases as the spacecraft moved away from Mercury. During the flybys, both signals are polluted by sporadic spikes whose origin remains uncertain.Despite these spikes, Ca was clearly detected by the c422 channel. The c422 signal shows not only an enhancement of Ca at dawn but also a very extensive Ca corona on the morning side, which was not reported by MESSENGER. The scale height deduced from our Ca profiles (2,500â2,800 km) is in agreement with the value reported by MESSENGER at similar true anomaly angle. Using the Chamberlain model, I determined a high temperature at the exobase (>50,000 K), in agreement with MESSENGER results. Both the large scale height and temperature at the exobase imply a very energetic release process. I also report a day/night asymmetry in the Ca exosphere that could indicate that the source of Ca is predominantly on the dayside or be the consequence of a shift of the main source of Ca away from the dawn region. The next step consists in using a 3D exospheric model that will include the effects of photoionization and non uniform distribution of Ca. Finally, PHEBUS pointing during the flybys did not allow to observe the potential cold component of Ca as the altitudes 50 000K), ce qui est en accord avec les rĂ©sultats de MESSENGER. La grande hauteur dâĂ©chelle et la tempĂ©rature Ă lâexobase Ă©levĂ©e impliquent un processus de libĂ©ration trĂšs Ă©nergĂ©tique. Les donnĂ©es semblent Ă©galement indiquer une asymĂ©trie jour/nuit qui pourrait signifier que la source de Ca est principalement du cĂŽtĂ© jour ou ĂȘtre la consĂ©quence dâun dĂ©calage de la source de Ca par rapport Ă la rĂ©gion de lâaube. La prochaine Ă©tape consiste Ă utiliser un modĂšle exosphĂ©rique 3D prenant en compte la photoionisation et la distribution non uniforme du Ca. Enfin, le pointage de PHEBUS lors de ces deux premiers survols nâa pas permis dâobserver la potentielle composante froide du Ca puisque les altitudes <200 km nâont pas Ă©tĂ© explorĂ©es.Le canal c404 a dĂ©tectĂ© une ou plusieurs espĂšces Ă basse altitude cĂŽtĂ© matin lors des survols, potentiellement du K ou du Mn. Cette ligne dâĂ©mission du K nâa jamais Ă©tĂ© dĂ©tectĂ©e par MESSENGER.Quant au Mn, MESSENGER ne lâa pas observĂ© continuellement, il nâa Ă©tĂ© dĂ©tectĂ© quâĂ certaines saisons et dans certaines rĂ©gions de lâexosphĂšre.Ces conditions de dĂ©tection sont bien diffĂ©rentes de celles de BepiColombo.Il est donc difficile dâidentifier avec certitude lâespĂšce dĂ©tectĂ©e. Dâautres observations sont nĂ©cessaires.On peut tout de mĂȘme mentionner que lâĂ©chelle de hauteur dĂ©duite du profil c404 est âŒ135 km et que le modĂšle de Chamberlain appliquĂ© au profil c404 semble indiquer une tempĂ©rature Ă lâexobase <3000 K
EUV reflectance of Mercury measured by BepiColombo/PHEBUS
International audienceBepiColombo will be inserted around Mercury in December 2025, but during the cruise phase, several opportunities to perform disk-integrated observations of Mercury are possible. The first observations of the illuminated surface of Mercury by PHEBUS (Probing of Hermean Environment by Ultraviolet Spectroscopy) with the EUV channel ( ⌠55-160 nm) were done on 9 and 10 Oct 2021, few days after the first flyby, from a distance of âŒ.03 AU at a phase angle of 72°. The solar reflected spectrum is detected from 80 nm to 160 nm. We present the EUV reflectance of Mercury derived from these observations and compare its spectral variations to the measurements by Mariner 10 done at few wavelengths in this spectral range and to the MESSENGER observations done at longer wavelengths
PHEBUS observations of the He 58.4 nm emission during Bepi Colombo's first Mercury Flyby
International audienceWe present observations of the He 58.4 nm emission performed with the EUV channel of the PHEBUS spectrometer on board ESAâs Mercury Planetary Orbiter during Bepi Colomboâs first Mercury Flyby in October 2021. We describe the data analysis and PHEBUS EUV calibration based on interplanetary He 58.4 nm data from observations during the cruise. We discuss the results in comparison with Mariner 10 measurements at 58.4 nm and models of Mercuryâs exosphere
PHEBUS observations of the He 58.4 nm emission during Bepi Colombo's first Mercury Flyby
International audienceWe present observations of the He 58.4 nm emission performed with the EUV channel of the PHEBUS spectrometer on board ESAâs Mercury Planetary Orbiter during Bepi Colomboâs first Mercury Flyby in October 2021. We describe the data analysis and PHEBUS EUV calibration based on interplanetary He 58.4 nm data from observations during the cruise. We discuss the results in comparison with Mariner 10 measurements at 58.4 nm and models of Mercuryâs exosphere
EUV reflectance of Mercury measured by BepiColombo/PHEBUS
International audienceBepiColombo will be inserted around Mercury in December 2025, but during the cruise phase, several opportunities to perform disk-integrated observations of Mercury are possible. The first observations of the illuminated surface of Mercury by PHEBUS (Probing of Hermean Environment by Ultraviolet Spectroscopy) with the EUV channel ( ⌠55-160 nm) were done on 9 and 10 Oct 2021, few days after the first flyby, from a distance of âŒ.03 AU at a phase angle of 72°. The solar reflected spectrum is detected from 80 nm to 160 nm. We present the EUV reflectance of Mercury derived from these observations and compare its spectral variations to the measurements by Mariner 10 done at few wavelengths in this spectral range and to the MESSENGER observations done at longer wavelengths
Observations of Mercuryâs Exosphere during BepiColombo First Mercury Flyby with PHEBUSâ visible channels
International audienceDuring the first flyby of Mercury with BepiColombo in October 2021, the ultraviolet spectrometer PHEBUS (Probing of Hermean Environment By Ultraviolet Spectroscopy) was able to observe with the two visible channels centered at 404 nm (K line) and 422 nm (Ca line). The observation started 30 minutes before Closest Approach and lasted one hour. The results clearly depict the geometry of observation, the spacecraft moving from the nightside of Mercury to its dayside. We also see some bursts on the count rate after the exit of Mercuryâs shadow, and discuss possible correlations with dust particles or the crossing of magnetospheric structures. We distinctly detect Calcium at 422nm and compare these results with MESSENGER data and an exospheric model
PHEBUS observations of the He 58.4 nm emission during Bepi Colombo's first Mercury Flyby
International audienceWe present observations of the He 58.4 nm emission performed with the EUV channel of the PHEBUS spectrometer on board ESAâs Mercury Planetary Orbiter during Bepi Colomboâs first Mercury Flyby in October 2021. We describe the data analysis and PHEBUS EUV calibration based on interplanetary He 58.4 nm data from observations during the cruise. We discuss the results in comparison with Mariner 10 measurements at 58.4 nm and models of Mercuryâs exosphere