Outbursts of comet nuclei are likely caused by surface avalanches rather than geyser-like eruptions from within, research by the Planetary Science Institute's Jordan Steckloff shows.

Rapid asymmetric brightening events of comets have been observed for decades and have long been thought to be the result of some sort of eruption of materials from deep within the interior of a comet, said Steckloff, a PSI Associate Research Scientist.

Steckloff's abstract "Are Comet Outbursts the Result of Avalanches?" was presented at a press conference at the joint 48th meeting of the American Astronomical Society (AAS) Division for Planetary Sciences (DPS) and 11th European Planetary Science Congress (EPSC) in Pasadena, California.

High-resolution images from Rosetta observations of 67P/Churyumov-Gerasimenko show outbursts that resemble plumes of material from geysers on Earth.

"However, there is a major problem with this model. There is no internal heat source on comets to power geyser-like eruptions," Steckloff said. "Instead, these outburst plumes are the natural result of avalanches."

The surfaces of comets have regions at the base of slopes and cliffs that are rich in icy materials, and are actively sublimating, with ice turning directly into gas. As this gas leaves the surface of the comet, it produced a weak breeze, Steckloff said. When granular materials on comets slide downslope or over a cliff, they enter this sublimation breeze and are blown into a tightly collimated plume of material that leaves the surface of the nucleus.

This model is consistent with data collected by the Rosetta spacecraft, and provides a physical mechanism that allows these outbursts to be studied to determine where on the surface they came from and how much material avalanched downslope.

"Ultimately, understanding this novel mechanism of outbursting may allow the surface processes of distant comets to be studied from Earth through ground-based observations of their outbursts," Steckloff said.