Summer outbursts in the coma of comet 67P/Churyumov–Gerasimenko as observed by Rosetta–VIRTIS

Abstract

We present an analysis of transient events observed by the Visible InfraRed Thermal Imaging Spectrometer, instrument aboard Rosetta, for the dates of 2015 August 10, September 13 and 14, during the two months surrounding the comet perihelion passage of the Rosetta spacecraft. We detected and characterized events with lifetimes ranging from 26 min down to 6 min. The temporal evolution of the outburst shows a sudden increase of radiance from quiescent coma to the maximum in a few minutes. This rapid onset is correlated with a change of the visible dust colour from red, 15-18± 3 per cent/100 nm, to bluer with values of 7-10± 0.3 per cent/100 nm. The dust morphology of these outbursts can be classified into two main types: narrow and collimated plumes (August 10, September 13) and broad blobs (September 14). The observations suggest that there are localized regions on the surface that are more prone to outbursts than the rest of the nucleus. The projected dust velocity during the outburst events ranges between 22.2 ± 2.2 m s −1 and 64.9 ± 10.6 m s −1. The total ejected mass during an outburst event is estimated to be between 10 and 500 tons for a duration of 6-26 min assuming size distribution indices between −2.5 and −3.

Cometary Comae-Surface Links

“…The dust material detected during the increase phase of the dust emission is associated with a large increase of the colour temperature (from 300 to 630 K) and a change of the dust colour in the visible and infrared spectra from red to blue, revealing the presence of very small grains (≤ 100 nm) with a velocity of 20-40 m/s. In addition, the measured large bolometric albedos (∼0.7) indicate bright grains in the ejecta, which could either be silicatic grains, implying thermal degradation of the carbonaceous material, or icy grains Rinaldi et al 2018). The far-ultraviolet spectrograph, Alice, onboard Rosetta observed the same outburst in the range between 70 and 205 nm.…”

“…( 2017 , 2019 ) and Rinaldi et al. ( 2018 ). The main results are the particle size distribution in the quiescent coma and the detection of high-temperature grains during outburst.…”

“…These considerations above have covered what may be referred to as the contiguous activity. In addition, short-term activity ("outbursts") has been observed on various time and spatial scales throughout the Rosetta mission Vincent et al 2016b;Rinaldi et al 2018). Outbursts occur not only in case of 67P but are typical for comets.…”

“…During perihelion 67P's activity led to rejuvenation of its surface, exposing underlying and mostly primordial material. A comprehensive study of the diffuse coma and outbursts observed with VIRTIS was presented by and Rinaldi et al (2018). The main results are the particle size distribution in the quiescent coma and the detection of high-temperature grains during outburst.…”

“… 2016a ; Rinaldi et al. 2018 ), characterised by a sudden increase of the dust emission, peaking a few minutes later, followed by a smooth decrease of the emission until it returns to the pre-outburst value. The dust material detected during the increase phase of the dust emission is associated with a large increase of the colour temperature (from 300 to 630 K) and a change of the dust colour in the visible and infrared spectra from red to blue, revealing the presence of very small grains ( ) with a velocity of 20–40 m/s.…”