New insights on the young ice deposits of Ceres

New insights on the young ice deposits of Ceres
by Clarence Oxford
Los Angeles CA (SPX) Apr 17, 2024

Ceres, the largest asteroid in our Solar System, features recently formed ice deposits in permanently shadowed craters near its poles, similar to those found on our Moon and Mercury. This similarity was first noted when the Dawn spacecraft surveyed Ceres in 2016, revealing bright ice deposits in these dark craters.

"The initial observation in 2016 opened up a mystery, with many of Ceres's polar craters shadowed throughout its 4.6 Earth-year-long year, yet only a select few contain ice deposits," explained Norbert Schorghofer, lead author of the study "History of Ceres's Cold Traps Based on Refined Shape Models." This study, published in The Planetary Science Journal, involved collaboration between PSI's Robert Gaskell, John Weirich, and Erwan Mazarico of NASA Goddard Space Flight Center.

Schorghofer further detailed how Ceres's rotation axis sways due to gravitational influences from the Sun and Jupiter, causing an oscillation every 24,000 years. "When the axis tilt increases, intensifying the seasons, fewer craters remain shadowed throughout the year, coinciding with the locations of these ice deposits," he added.

To better understand the shadow dynamics in these craters, researchers used digital elevation models and ray-tracing techniques to simulate past shadow coverage. This approach highlighted the precision of digital models in predicting the extent of cold, shadowed areas.

"The last time Ceres's axis tilt peaked, around 14,000 years ago, no crater remained in permanent shadow, suggesting any ice would have sublimated," Schorghofer noted. This timing indicates that the current ice deposits are less than 6,000 years old, making them geologically very young.

This discovery was supported by PSI scientist Tom Prettyman's 2017 findings, which showed widespread shallow ice on Ceres. This ice, when disturbed by a dry impactor, possibly an asteroid fragment around 6,000 years ago, could have vaporized to form a temporary atmosphere, subsequently freezing in the coldest craters.

The study also explored the possibility of non-water ices in Ceres's craters. Despite the extreme cold, only water ice seems to persist, likely due to Ceres's current 4-degree axis tilt which allows more sunlight into the craters compared to the Moon's 1.5-degree tilt.

Schorghofer's team's new mapping techniques and temperature calculations offer a fresh understanding of these ice deposits. "The events that led to these deposits are almost as recent as human civilization itself," he concluded.

Research Report:History of Ceres's Cold Traps Based on Refined Shape Models