NASA's Dawn space probe has identified several shadowed regions and craters on dwarf planet Ceres considered as "cold traps" or areas where ice can likely accumulate over time.
Most of these permanently shadowed areas are cold enough to trap water ice for billions of years, scientists say. This raises the possibility that ice deposits currently exist in these cold traps.
Guest investigator Norbert Schorghofer of the University of Hawaii at Manoa says the conditions on the dwarf planet are just enough for the accumulation of water ice deposits.
Ceres has the right mass to hold on to water molecules, Schorghofer says. Plus, the dwarf planet's extremely cold shadowed regions are even more frigid than regions on Mercury or on the moon.
How Shadowed Regions Become Cold Traps
Cold traps have long been predicted for Ceres, but have not been detected until now.
Schorghofer and his colleagues studied the northern hemisphere of Ceres. Images from the Dawn probe's cameras were combined to determine the shape of the dwarf planet, showing plains, craters and other features.
A sophisticated computer model at NASA's Goddard Space Flight Center helped pinpoint which areas receive direct sunlight, how conditions on the dwarf planet change over the course of a year and how much solar radiation reaches its surface.
It's important to note that direct sunlight does not reach Ceres' permanently shadowed regions, which are usually located along a section of the crater or on the crater floor.
Still, these regions do receive indirect sunlight. However, if the temperature plummets below negative 240 degrees Fahrenheit (negative 151 degrees Celsius), the shadowed areas then become cold traps, scientists say.
Expansive Shadowed Regions
Schorghofer and his team discovered plenty of large permanently shadowed regions all across Ceres' northern hemisphere. The largest region is inside a crater that is 16 kilometers (10 miles) wide situated less than 65 kilometers (40 miles) from Ceres' north pole.
When added together, the permanently shadowed regions on Ceres occupy about 1,800 square kilometers (695 square miles) of land. This is only a small fraction of its landscape -- about 1 percent of the northern hemisphere's surface area.
Another guest investigator from Goddard, Erwan Mazarico, says because Ceres is far from the sun and the shadowed areas receive little radiation, the dwarf planet's shadowed regions are colder than that on Mercury and the moon.
"On Ceres, these regions act as cold traps down to relatively low latitudes," says Mazarico.
On the other hand, on Mercury and the Earth's moon, only the permanently shadowed regions close to the poles become enough for ice to stabilize on the surface.
Furthermore, the situation on Ceres is more similar to the situation on Mercury, scientists say. The shadowed regions on Mercury expands roughly the same fraction of the northern hemisphere. Mercury's efficiency to trap water ice is also comparable to Ceres.
Chris Russell, the Dawn mission's principal investigator, adds that Ceres may have been formed with a greater reservoir of water compared to the moon and Mercury. Some studies suggest that Ceres may be a volatile-rich world that does not rely on current-day external sources.
Details of the study are featured in the journal Geophysical Research Letters.
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