Reflectivity of Venus’s 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 52–1700 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 283–800 nm wavelengths. Considerable absorption is present in the 350–450 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 l’exosphère de Mercure par le spectromètre 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 Mercury’s 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 Mercury’s 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 ∼200 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 (2,500–2,800 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 résultats de MESSENGER. La grande hauteur d’échelle et la température à l’exobase élevée impliquent un processus de libération très énergétique. Les données semblent également indiquer une asymétrie jour/nuit qui pourrait signifier que la source de Ca est principalement du côté jour ou être la conséquence d’un décalage de la source de Ca par rapport à la région de l’aube. La prochaine étape consiste à utiliser un modèle exosphérique 3D prenant en compte la photoionisation et la distribution non uniforme du Ca. Enfin, le pointage de PHEBUS lors de ces deux premiers survols n’a pas permis d’observer la potentielle composante froide du Ca puisque les altitudes <200 km n’ont pas été explorées.Le canal c404 a détecté une ou plusieurs espèces à basse altitude côté matin lors des survols, potentiellement du K ou du Mn. Cette ligne d’émission du K n’a jamais été détectée par MESSENGER.Quant au Mn, MESSENGER ne l’a pas observé continuellement, il n’a été détecté qu’à certaines saisons et dans certaines régions de l’exosphère.Ces conditions de détection sont bien différentes de celles de BepiColombo.Il est donc difficile d’identifier avec certitude l’espèce détectée. D’autres observations sont nécessaires.On peut tout de même mentionner que l’échelle de hauteur déduite du profil c404 est ∼135 km et que le modèle de Chamberlain appliqué au profil c404 semble indiquer une température à l’exobase <3000 K

Etude de l’exosphère de Mercure par le spectromètre PHEBUS de la mission BepiColombo

Mercure est la planète tellurique la moins explorée du système solaire, trois missions seulement l’ont survolée. Mariner 10 a effectué trois survols de la planète en 1974 et 1975, découvrant une atmosphère très mince, similaire à celle de la Lune, contenant de l’hélium (He) et de l’hydrogène (H). Le sodium (Na), le potassium (K) et le calcium (Ca) ont été détectés plus tard à partir d’observations depuis la Terre. La mission MESSENGER, lancée en 2004, a non seulement survolé Mercure à trois reprises mais a également orbité la planète durant quatre ans. Elle a détecté deux nouvelles espèces, le magnésium (Mg) et le manganèse (Mn). En parallèle, deux autres espèces ont été découvertes grâce à des observations depuis la Terre : le fer (Fe) et l’aluminium (Al). BepiColombo est la troisième mission à destination de Mercure. Lancée en 2018, la mission conjointe ESA JAXA doit effectuer six survols de Mercure avant de s’insérer en orbite fin 2025. Trois survols de Mercure ont déjà été réalisés lors desquels PHEBUS (Probing the Hermean Exosphere By Ultraviolet Spectroscopy) a pu observer l’exosphère de Mercure. L’instrument est composé de deux détecteurs UV (EUV et FUV) et de deux canaux visibles (c404 et c422). Le canal c404 est dédié à la ligne d’émission du K à 404,7 nm tandis que le canal c422 est dédié à la ligne d’émission du Ca à 422,8 nm. La géométrie d’observation des deux premiers survols est similaire, la sonde approchant la planète côté nuit, traversant son ombre avant de se diriger côté jour. La sonde s’est approchée à ∼200 km de la surface au point le plus proche côté nuit. PHEBUS pointait vers le nord, dans une direction opposée au soleil. Le taux de comptage enregistré par les deux canaux visibles illustre la géométrie d’observation, notamment le passage dans l’ombre de Mercure. Le maximum est atteint peu après la sortie d’éclipse. Le taux de comptage diminue ensuite à mesure que la sonde s’éloigne de Mercure. Lors des survols, les signaux des deux canaux sont pollués par des pics sporadiques dont l’origine reste incertaine. Malgré ces pics, le canal c422 a clairement détecté du Ca. Le signal c422 montre non seulement une concentration de Ca à l’aube mais également une couronne de Ca très étendue du côté matin qui n’a pas été rapportée par MESSENGER. La hauteur d’échelle déduite de nos profils (2500-2800 km) est en accord avec la valeur rapportée par MESSENGER à un angle d’anomalie vraie similaire. En utilisant le modèle de Chamberlain, j’ai déterminé une température à l’exobase très élevée (>50 000K), ce qui est en accord avec les résultats de MESSENGER. La grande hauteur d’échelle et la température à l’exobase élevée impliquent un processus de libération très énergétique. Les données semblent également indiquer une asymétrie jour/nuit qui pourrait signifier que la source de Ca est principalement du côté jour ou être la conséquence d’un décalage de la source de Ca par rapport à la région de l’aube. La prochaine étape consiste à utiliser un modèle exosphérique 3D prenant en compte la photoionisation et la distribution non uniforme du Ca. Enfin, le pointage de PHEBUS lors de ces deux premiers survols n’a pas permis d’observer 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 ∼135 km and that the Chamberlain model applied to the c404 profile seems to indicate a temperature at the exobase <3000 K

Etude de l’exosphère de Mercure par le spectromètre 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 Mercury’s 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 Mercury’s 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 ∼200 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 (2,500–2,800 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 résultats de MESSENGER. La grande hauteur d’échelle et la température à l’exobase élevée impliquent un processus de libération très énergétique. Les données semblent également indiquer une asymétrie jour/nuit qui pourrait signifier que la source de Ca est principalement du côté jour ou être la conséquence d’un décalage de la source de Ca par rapport à la région de l’aube. La prochaine étape consiste à utiliser un modèle exosphérique 3D prenant en compte la photoionisation et la distribution non uniforme du Ca. Enfin, le pointage de PHEBUS lors de ces deux premiers survols n’a pas permis d’observer la potentielle composante froide du Ca puisque les altitudes <200 km n’ont pas été explorées.Le canal c404 a détecté une ou plusieurs espèces à basse altitude côté matin lors des survols, potentiellement du K ou du Mn. Cette ligne d’émission du K n’a jamais été détectée par MESSENGER.Quant au Mn, MESSENGER ne l’a pas observé continuellement, il n’a été détecté qu’à certaines saisons et dans certaines régions de l’exosphère.Ces conditions de détection sont bien différentes de celles de BepiColombo.Il est donc difficile d’identifier avec certitude l’espèce détectée. D’autres observations sont nécessaires.On peut tout de même mentionner que l’échelle de hauteur déduite du profil c404 est ∼135 km et que le modèle de Chamberlain appliqué au profil c404 semble indiquer une température à l’exobase <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 ∼.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 ESA’s Mercury Planetary Orbiter during Bepi Colombo’s 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 Mercury’s 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 ESA’s Mercury Planetary Orbiter during Bepi Colombo’s 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 Mercury’s 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 ∼.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 Mercury’s Exosphere during BepiColombo First Mercury Flyby with PHEBUS’ 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 Mercury’s 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 ESA’s Mercury Planetary Orbiter during Bepi Colombo’s 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 Mercury’s exosphere