Chinese Scientists Identify Rocket Effect Behind Boulder Movement on Comet

Chinese Scientists Identify "Rocket Effect" Behind Boulder Movement on Comet
by Simon Mansfield
Sydney, Australia (SPX) Feb 21, 2025

Chinese researchers have determined that the unexpected displacement of a boulder on a comet's surface was caused by a "rocket effect," driven by the uneven outburst of volatile ice within the boulder.

Their study, published in *The Astrophysical Journal*, is based on observations made by the European Space Agency's (ESA) Rosetta spacecraft during its extensive survey of comet 67P/Churyumov-Gerasimenko from 2014 to 2016.

In 2015, Rosetta recorded the boulder shifting approximately 140 meters northward as the comet approached its closest point to the Sun. A team led by Shi Xian from the Shanghai Astronomical Observatory, part of the Chinese Academy of Sciences, examined high-resolution imagery and thermal data, concluding that irregular sublimation of ice inside the boulder generated a thrust force, propelling it across the comet's surface.

Comets are composed of a nucleus primarily made of ice and rock. When far from the Sun, the nucleus remains inactive, but as the comet moves closer, solar heating causes the ice to sublimate, lifting dust and forming a surrounding coma and trailing tail.

By reconstructing the thermal history of the boulder and its surroundings, the scientists observed a significant temperature disparity between its southern and northern sides. During the movement, the southern side experienced peak internal heating, whereas the northern side remained notably cooler.

This imbalance led the researchers to propose a new mechanism explaining the boulder's movement. The sublimation-driven outburst occurring predominantly on one side created a reactive thrust-similar to a small-scale rocket engine-propelling the boulder downslope along the northern terrain.

Furthermore, the researchers detailed the sequence of events before and after the boulder's movement. They identified frequent nighttime dust ejections in the region, which they suggest resulted from the boulder's shift, exposing fresh, volatile-rich ice beneath it.

Shi emphasized the importance of studying comets, which serve as relics from the early solar system and provide insights into planetary formation and evolution.

"With each discovery, we are uncovering an increasingly diverse range of cometary activities. Understanding these dynamic processes will enhance our knowledge of the solar system's history and possibly the origins of life," Shi stated.