Astronomers have now figured out the mechanism behind the brief but powerful outbursts in the surface of the Comet 67P/Churyumov-Gerasimenko that was captured by the Rosetta spacecraft in 2015.
Their findings, described in a paper published in the journal Monthly Notices of the Royal Astronomical Society, suggests that the outbursts, which were more violent than the regular jets of dust and gas, were coming from the comet's nucleus and were triggered by the rapid change in local temperature.
"The team found that just over half of the events occurred in regions corresponding to early morning, as the Sun began warming up the surface after many hours in darkness," the astronomers explained in a press release. "The rapid change in local temperature is thought to trigger thermal stresses in the surface that might lead to a sudden fracturing and exposure of volatile material. This material rapidly heats up and vaporizes explosively."
On Aug. 13, 2015, Rosetta captured 34 outbursts from Comet 67P during the comet's closest approach to the sun. These outbursts appeared to be brighter than the usual jets and believed to release 60-260 tons of material.
Outbursts can be categorized into three, depending on the appearance of its dust flow. One category of outbursts is associated with a long, narrow jet extending far from the nucleus. The second category involves a broad, wide base that expands more laterally. Meanwhile, the third category is described as a complex hybrid between the two categories.
However, outbursts tend to be short-lived making only possible to be captured once. Due to this, researchers were not able to determine if the image was taken shortly after the outburst started or later in the process.
As a result, astronomers can't tell if the different categories of outburst have different corresponding mechanisms. If the three categories are taken to be part of a single process, the astronomers hypothesize that the process starts with a long narrow jet with dust ejected at high speed, modifying the surface around the exit point. Due to the altered surface, a larger fraction of fresh material is exposed, broadening the plume "base." As the surface modification continues, it is most likely that the source region is not able to support the narrow jet anymore, resulting to only broad plumes.