Abstract
The OSIRIS camera onboard the Rosetta spacecraft obtained close-up views of the dust coma of comet 67P. The jet structures can be used to trace their source regions and to examine the possible effect of gas-surface interaction. Methods. We analyzed the wide-angle images obtained in the special dust observation sequences between August and September 2014. The jet features detected in different images were compared to study their time variability. The locations of the potential source regions of some of the jets are identified by ray tracing. We used a ring-masking technique to calculate the brightness distribution of dust jets along the projected distance. Results. The jets detected between August and September 2014 mostly originated in the Hapi region. Morphological changes ap- peared over a timescale of several days in September. The brightness slope of the dust jets is much steeper than the background coma. This might be related to the sublimation or fragmentation of the emitted dust grains. Interaction of the expanding gas flow with the cliff walls on both sides of Hapi could lead to erosion and material down-fall to the nucleus surface.
Highlights
In the last perihelion approach of 67P/Churymov-Gerasimenko in 2008–2009, its dust coma activity was monitored by ground-based observations (Lara et al 2011; Tozzi et al 2011)
Soon after the achievement of spatially resolved images of the dust coma of 67P in July 2014 (Sierks et al 2015), the morphology and temporal variation of a set of dust jets have been under close scrutiny by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS)
We found that the jet brightness slopes vary between 0.95 ± 0.03 and 1.48 ± 0.08, whereas those of the corresponding background comas vary between 0.41 ± 0.04 and 0.59 ± 0.17
Summary
In the last perihelion approach of 67P/Churymov-Gerasimenko (hereafter 67P) in 2008–2009, its dust coma activity was monitored by ground-based observations (Lara et al 2011; Tozzi et al 2011). Soon after the achievement of spatially resolved images of the dust coma of 67P in July 2014 (Sierks et al 2015), the morphology and temporal variation of a set of dust jets have been under close scrutiny by the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS). This gives us an important opportunity to investigate the gradual development of the outgassing effect as the comet approaches the Sun. In the following, we describe the OSIRIS observations in the initial phase of the rendezvous mission between August and September 2014.
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