The EUV Reflectance of Mercury's Surface Measured by BepiColombo/PHEBUS

• Published in: Journal of geophysical research. Planets Vol. 128; no. 3
• Main Authors: Chaufray, J.‐Y., Quémerais, E., Koutroumpa, D., Robidel, R., Leblanc, F., Réberac, A., Yoshikawa, I., Yoshioka, K., Murakami, G., Korablev, O., Belyaev, D., Pelizzo, M. G., Corso, A. J.
• Format: Journal Article
• Language: English
• Published: 01.03.2023
• Subjects: Mercury; reflectance
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2022JE007669

On 9 and 10 October 2021, Probing the Hermean Exosphere by Ultraviolet Spectroscopy aboard BepiColombo observed the disk‐integrated reflected light from the Sun by Mercury in the spectral range 90–160 nm at a phase angle of 70°. These observations are used to derive the EUV reflectance of the surface of Mercury in this wavelength range for the first time since the Mariner 10 observations in 1974–1975. Our observations are in agreement with a surface of Mercury darker by a factor ∼0.5–0.6 compared to the Moon in this wavelength range, with an average reflectance of 0.3% at a phase angle of 70°. This lower reflectance of Mercury could be due to the lower abundance of FeO. The derived reflectance near 160 nm is close to the derived reflectance at 220 nm by MESSENGER/MASCS at a similar phase angle. Possible spectral variations measured between 110 and 140 nm could be attributed to SiO2 glass, but the signal to noise ratio is low and other observations, possible at several periods during the rest of the cruise, are needed to confirm this last result. Plain Language Summary Due to the lack of atmosphere, the solar UV radiation directly impacts the surface of Mercury. A fraction of this radiation is reflected into space in all directions. This reflected fraction varies with wavelength and can be analyzed to constrain the composition and texture of the surface of Mercury. Probing the Hermean Exosphere by Ultraviolet Spectroscopy aboard BepiColombo observed the reflected radiation between 90 and 160 nm for the first time since the Mariner 10 observations in 1974–1975. In this study, we measure the fraction of UV radiation reflected at different wavelengths. We compare our results with past observations from Mariner 10. We explain part of the observed spectral variations as possible due to the presence of SiO2 glass at the surface of Mercury and an albedo lower than the Moon due to a lower abundance of FeO. Key Points We derive the reflectance of Mercury's surface between 90 and 160 nm for the first time since Mariner 10 The lower albedo of Mercury compared to the Moon could be due to a lower FeO concentration but other opaque species may be needed Some spectral variations could possibly be due to SiO2