Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta

Tubiana, C. and Rinaldi, G. and Güttler, C. and Snodgrass, C. and Shi, X. and Tóth, Imre (2019) Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta. ASTRONOMY & ASTROPHYSICS, 630. ISSN 0004-6361

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Abstract

Context. On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS an VIRTIS-M instruments on board the Rosetta spacecraft simultaneousl observed the evolving dust and gas coma during a complete rotation o the comet. Aims: We aim to characterize the spatial distributio of dust, H2O, and CO2 gas in the inner coma. To d this, we performed a quantitative analysis of the release of dust an gas and compared the observed H2O production rate with th rate we calculated using a thermophysical model. Methods: Fo this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS- image cubes at 612 nm, 2700 nm (H2O emission band), and 420 nm (CO2 emission band). We measured the average signal in circular annulus to study the spatial variation around the comet, and i a sector of the annulus to study temporal variation in the sunwar direction with comet rotation, both at a fixed distance of 3.1 km fro the comet center. Results: The spatial correlation between dus and water, both coming from the sunlit side of the comet, shows tha water is the main driver of dust activity in this time period. Th spatial distribution of CO2 is not correlated with water an dust. There is no strong temporal correlation between the dus brightness and water production rate as the comet rotates. The dus brightness shows a peak at 0° subsolar longitude, which is no pronounced in the water production. At the same epoch, there is also maximum in CO2 production. An excess of measured wate production with respect to the value calculated using a simpl thermophysical model is observed when the head lobe and regions of th southern hemisphere with strong seasonal variations are illuminate (subsolar longitude 270°-50°). A drastic decrease in dust productio when the water production (both measured and from the model) displays maximum occurs when typical northern consolidated regions ar illuminated and the southern hemisphere regions with strong seasona variations are instead in shadow (subsolar longitude 50°-90°). Possibl explanations of these observations are presented and discussed

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