Chinese Scientists Identify Rocket Effect as Key Driver of Boulder Motion on Comet

Chinese Scientists Identify "Rocket Effect" as Key Driver of Boulder Motion on Comet
by Simon Mansfield
Sydney, Australia (SPX) Feb 21, 2025

A team of Chinese scientists has linked the unexpected movement of a boulder on Comet 67P/Churyumov-Gerasimenko to a process known as the "rocket effect." This phenomenon, triggered by the uneven sublimation of volatile ice within the boulder, was observed by the European Space Agency's (ESA) Rosetta spacecraft during its mission between 2014 and 2016.

The study, recently published in *The Astrophysical Journal*, analyzed data from Rosetta, which documented the boulder's displacement by approximately 140 meters northward in 2015, near the comet's closest approach to the Sun. Researchers led by Shi Xian of the Shanghai Astronomical Observatory (CAS) examined high-resolution imagery and thermal readings to determine that the boulder's motion was driven by asymmetrical outgassing, creating a force strong enough to propel it across the comet's surface.

Comets primarily consist of a nucleus composed of rock, dust, and frozen gases. When located far from the Sun, a comet remains dormant. However, as it nears the Sun, the nucleus heats up, causing the ice to sublimate and release gas and dust, forming a glowing coma and a trailing tail.

By investigating the boulder's thermodynamic history, scientists identified uneven heat distribution between its northern and southern sides. The southern side exhibited a peak temperature while the northern side remained notably cooler. This temperature contrast, they concluded, led to localized pressure buildup and sudden sublimation of internal ice, resulting in a forceful expulsion of gas that acted like a propulsion system, pushing the boulder downhill.

Further analysis of the surrounding region revealed that after the boulder's movement, there was an increase in nighttime dust ejections. Researchers believe these outbursts occurred due to the exposure of subsurface ice layers, disturbed during the displacement.

Shi emphasized the importance of studying comets, as they are remnants from the early solar system and hold valuable information about its formation and evolution.

"As our research progresses, we're discovering unexpectedly diverse comet activities. Understanding the mechanisms behind these could help us unveil the mysteries of the solar system's evolution and the origins of life," Shi stated.