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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 and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet.Aims.We aim to characterize the spatial distribution of dust, H2O, and CO2gas in the inner coma. To do this, we performed a quantitative analysis of the release of dust and gas and compared the observed H2O production rate with the rate we calculated using a thermophysical model.Methods.For this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS-M image cubes at 612 nm, 2700 nm (H2O emission band), and 4200 nm (CO2emission band). We measured the average signal in a circular annulus to study the spatial variation around the comet, and in a sector of the annulus to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet center.Results.The spatial correlation between dust and water, both coming from the sunlit side of the comet, shows that water is the main driver of dust activity in this time period. The spatial distribution of CO2is not correlated with water and dust. There is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. The dust brightness shows a peak at 0° subsolar longitude, which is not pronounced in the water production. At the same epoch, there is also a maximum in CO2production. An excess of measured water production with respect to the value calculated using a simple thermophysical model is observed when the head lobe and regions of the southern hemisphere with strong seasonal variations are illuminated (subsolar longitude 270°–50°). A drastic decrease in dust production when the water production (both measured and from the model) displays a maximum occurs when typical northern consolidated regions are illuminated and the southern hemisphere regions with strong seasonal variations are instead in shadow (subsolar longitude 50°–90°). Possible explanations of these observations are presented and discussed.
Highlights
After a ten-year journey and 30 months of deep-space hibernation, the ESA Rosetta spacecraft woke up on 20 January 2014
In this work we study temporal variation in more detail, and can better study areas of the dust continuum that were heavily affected by stray light in the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS)-M data by combining it with OSIRIS imaging
Summary and conclusion We have analyzed one OSIRIS and one VIRTIS-M dataset acquired on 27 April 2015, when the comet was at 1.76 au from the Sun in the inbound arc
Summary
After a ten-year journey and 30 months of deep-space hibernation, the ESA Rosetta spacecraft woke up on 20 January 2014. Observations of dust jets have been traced to certain areas of the surface (Vincent et al 2016), and various models have been developed to trace gas and dust flow in the inner coma of 67P, with varying degrees of complexity (e.g., Fougere et al 2016; Kramer & Noack 2016; Kramer et al 2017; Zakharov et al 2018), but the models do not yet uniquely identify the surface features that are responsible for activity. Many of the models show that the bulk activity can be explained by more or less homogeneous activity from all illuminated surface facets (Keller et al 2015) and that jets in the inner coma are controlled more by the complex shape of the nucleus than by anything special about their apparent source on the surface (Shi et al 2018a). There are clear variations in activity with seasonal illumination of the
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