A long-held suspicion appears to be confirmed, as permanently shadowed regions have been found on the dwarf planet Ceres—meaning these areas could potentially be billion-year-old traps for water ice, according to NASA.
“The conditions on Ceres are right for accumulating deposits of water ice,” said Norbert Schorghofer, a Dawn guest investigator at the University of Hawaii at Manoa. “Ceres has just enough mass to hold on to water molecules, and the permanently shadowed regions we identified are extremely cold — colder than most that exist on the moon or Mercury.”
As the name implies, a permanently shadowed region receives no direct sunlight, being located on crater floors and similar areas. Of course, they still can receive indirect sunlight—but not all that much, as the temperature often hovers below minus 240 degrees Fahrenheit (minus 151 degrees Celsius). Because of this, permanently shadowed areas can be cold traps, meaning they’re good places for water ice to gather and remain stable.
Ceres findings confirm previous predictions
The existence of such traps on Ceres was predicted, but none had been discovered until now, when Schorghofer and his team took a hard look at Ceres’ northern hemisphere. After combining images taken by the Dawn spacecraft to create a depiction of the dwarf planet’s shape and features in three dimensions, a sophisticated computer model was able to determine which areas received direct sunlight, how much solar radiation reached the dwarf planet’s surface, and how conditions change with time, according to a study in Geophysical Research Letters.
The model found that there are dozens of permanently shadowed regions across Ceres’ northern hemisphere, which only occupy a small portion of the surface—some 695 square miles. But these dark spaces are extraordinarily cold, even colder than similar ones found on Mercury or the moon, which are closer to the sun (although Mercury is a closer approximation).
“On Ceres, these regions act as cold traps down to relatively low latitudes,” said Erwan Mazarico, a Dawn guest investigator. “On the moon and Mercury, only the permanently shadowed regions very close to the poles get cold enough for ice to be stable on the surface.”
According to the recent research, about one of every thousand water molecules generated on Ceres’ surface ends up in a cold trap within one Ceres’ year (1,682 days), meaning small but detectable ice deposits build up every 100,000 years or so.
“While cold traps may provide surface deposits of water ice as have been seen at the moon and Mercury, Ceres may have been formed with a relatively greater reservoir of water,” said Chris Russell, principal investigator of the Dawn mission, based at the University of California, Los Angeles. “Some observations indicate Ceres may be a volatile-rich world that is not dependent on current-day external sources.”
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Image credit: NASA
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