The release of gases by sublimation (the transition of ice into a gaseous state without a water stage) is the determining process for comets. However, a new study indicates that periodic landslides and avalanches (mass depletion) can become a cause that retains cometary activity for a long time period.
The released gases pull dust from the comet, forming a whole dust cloud, which can be observed from the Earth. Moreover, gas release events can change the state of rotation of an object. But with the sublimation of ice, the process should stop, fixing a dust layer on the surface, isolating the remaining ice stocks. Therefore, for a long time, it remained unknown how comets manage to maintain activity.
Scientists believe that landslides and landslides can release buried ice, allowing the comet to activate the process of sublimation. But mass depletion over time leads to smoothing of formations (mountains, rocks, elevations) on the cometary surface, which reduces the number and frequency of mass depletion events (landslides).
The sequence of images demonstrates various types of landslides on comet 67 / Churyumov-Gerasimenko. The first frame is a crack before the fall (July 10, 2015). Images from July 15 and December 26 display vivid initial material that appeared during the collapse of the rock. The brightness level by the 26th was reduced by 50%, which is explained by the sublimation of most of the open water ice. Pictures from 2016 show different types of new cliff tops. By August, most of them had returned to the average brightness of the comet. The arrows indicate the location of the gap and open water ice The researchers created two new models to study the activity of the comet in two ways. The first was based on terrestrial observations of cometary light curves and gas sublimation rates. The second considered how gases press down on the surface of the comet. It was important for these models to be in agreement with each other, since they describe one phenomenon.
When comparing, it turned out that models are able to agree only if elements of sublimation arise from elevations prone to collapse. That is, landslides and avalanches are crucial, which allow the comet to maintain activity. In addition, this process also ensures the reactivation of sleeping comets. If a change in the state of rotation or other processes can cause mass depletion, then the released ice will trigger a powerful sublimate activity.
There is, for example, the assumption that comet Enke most of the time remained in a sleeping state. But a serious mechanism of collapse launched the process of “awakening” and presented the object being observed now. Comets need detailed study, as they could play an important role in the formation of the solar system.