Terrestrial OH nightglow measurements during the Rosetta flyby

Abstract

We present a study of the terrestrial hydroxyl nightglow emissions observed with the Visible and Infrared Thermal Imaging Spectrometer on board the Rosetta mission. During these observations, the OH Δv = 1 and 2 sequences were measured simultaneously. This allowed investigating the relative population of the v = 1 to 9 vibrational levels by using both sequences. In particular, the relative population of the vibrational level v = 1 is determined for the first time from observations. The vibrational population decreases with increasing vibrational quantum number. A good agreement is found with a recent model calculation assuming multiquantum relaxation for OH(v) quenching by O2 and single‐quantum relaxation for OH(v) by N2.

Three-dimensional direct simulation Monte-Carlo modeling of the coma of comet 67P/Churyumov-Gerasimenko observed by the VIRTIS and ROSINA instruments on board Rosetta

“…Similarly, Hässig et al (2015) observed heterogeneities in the coma of 67P with large fluctuations in composition from ROSINA data from August and September 2014. This was confirmed by the VIRTIS-H measurements of 67P from November 2014 to January 2015 (Bockelée-Morvan et al 2015) and the VIRTIS-M mapping of very inner coma of 67P during mid-April 2015 (Migliorini et al 2016). Indeed, the VIRTIS-M observations followed the evolution of the coma of comet 67P with an unprecedented spatial resolution of about 40 m/pixel, showing that H 2 O is mostly emanating from the neck connecting the two principal lobes, while CO 2 emanates mostly from both the so-called head and southern latitude regions of the large lobe (Migliorini et al 2016).…”

“…This was confirmed by the VIRTIS-H measurements of 67P from November 2014 to January 2015 (Bockelée-Morvan et al 2015) and the VIRTIS-M mapping of very inner coma of 67P during mid-April 2015 (Migliorini et al 2016). Indeed, the VIRTIS-M observations followed the evolution of the coma of comet 67P with an unprecedented spatial resolution of about 40 m/pixel, showing that H 2 O is mostly emanating from the neck connecting the two principal lobes, while CO 2 emanates mostly from both the so-called head and southern latitude regions of the large lobe (Migliorini et al 2016). Moreover, VIRTIS-M has observed the diurnal cycle of the water ice in the neck regions, occurring in the form of transient deposits formed in the upper layer of the surface by recondensation of water molecules sublimated from the subsurface ice (De Sanctis et al 2015).…”

“…Finally, f k represents the heterogeneity of outgassing activity at the surface of the nucleus. Indeed, contrary to the assumption made in Bieler et al (2015), it was observed extensively that the nucleus of comet 67P does not release gas in a uniform manner (Migliorini et al 2016;Bockelée-Morvan et al 2015;Biver et al 2015;Feldman et al 2015). The f k depends on the species type since the main regions of gas release have been observed to be different for H 2 O and CO 2 Bockelée-Morvan et al 2015;Migliorini et al 2016).…”

“…While a complete description and interpretation of the VIRTIS-M and -H data can be found in Migliorini et al (2016) and Bockelée-Morvan et al (2015), respectively, the ROSINA-DFMS data requires a more complete characterization because we present a substantial number of new measurements.…”

“…We show some direct outputs of the DSMC model for both species giving macroscopic parameters such as gas density and velocity in the cometary coma. Then, we compare results from the DSMC model with DFMS measurements and with a set of VIRTIS-M images of the H 2 O and CO 2 coma taken at different illumination phases from Migliorini et al (2016), and with VIRTIS-H column densities over a two month period from Bockelée-Morvan et al (2015). Finally, the model is used to compute accurately the evolution of the H 2 O and CO 2 production rates with heliocentric distance as observed by the various instruments.…”