Study shows landslides and avalanches could keep comets active on the long run. Pictured, sequence of images showing different views of the Aswan cliff collapse on Comet 67P/Churyumov–Gerasimenko. ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA; Pajola et al. (2017)

Comets are snowballs made from frozen gases, rock, and dust that keeping orbiting the sun, giving away a distinct tail over a very long period.

The tail makes up the defining characteristic of these objects and has been witnessed by many across the globe. Scientists already knew it was driven by the process of sublimation where water ice warms up from solar energy and turns directly into a pronounced cloud. But, nobody really understands how these objects maintain this activity over many orbits.

Theoretically, the release of gas and dust from a comet should wipe out the ice, change its spin state, and silence all the activity, but observations taken over long time spans, clearly suggested a different case of prolonged activity.

To find an appropriate answer to the puzzle, Jordan K. Steckloff and Nalin H. Samarasinha from Planetary Science Institute, Arizona, ran a series of computer simulations analyzing cometary dynamics and how gases releasing from comets’ surface generate torques capable of changing their spin state.

“Nalin’s model is based on Earth-based observations of comet light curves and observed gas sublimation rates,” Steckloff said in a statement. “In contrast, my model considers how gases push on the surface of the comet as they escape, accounting for the effects of a comets’ activity, shape, and topography.”

As the two models took different approaches to describe the same phenomenon, the team compared the simulations to see if they are consistent with each other. The work revealed the models agreed only when sublimative torques originated primarily from steep, mass-wasting slopes.

Put simply, mass-wasting events occurring from the spin changes of a comet such as avalanches and landslides can expose buried subsurface ice on the object and refuel the process of sublimation on the body in question. The cycle, as the team posited, would be disrupted only when flattening features are left on the surface of the comet.

“We were trying to understand how cometary activity would affect their rotation,” Samarasinha said in the statement. “In the process, we were able to explore the long-term evolution of cometary activity and conjecture how the surface layers of short-period comets might evolve.”

That said, it is also worth noting the researchers think the same mass-wasting processes trigger activity on comets that have been dormant for a long time. This, as they said, explained how comets like 2P/Encke, which was considered to be dormant during its evolutionary stages, remain active at the moment.

“By understanding the physical processes occurring on the surfaces and in the surface layers of comets, we can provide the overall context to accurately interpret observations of comets,” Samarasinha concluded. “An in-depth understanding of comets help us ascertain the role played by these building blocks of the giant planets in the formation of the Solar System and also the various roles played by comets throughout the history of the Solar System.”

The study titled, "The sublimative torques of Jupiter Family Comets and mass wasting events on their nuclei,” was published in the journal Icarus.