Ceres’ surface has cold regions that can trap water ice
At the poles of Ceres, scientists have found craters that are permanently in shadow (indicated by blue markings). Such craters are called “cold traps” if they remain below about –240 °F (–151 °C). (Click to enlarge) Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Using data from cameras aboard NASA’s Dawn spacecraft, as well as computer models, mission scientists have identified areas on the surface of Ceres’ northern hemisphere that never receive sunlight and are, therefore, capable of trapping water ice.
The depths of craters or crater walls facing Ceres‘ north pole are in permanent shadow, receiving at most indirect sunlight. As a result, they are extremely cold.
If these regions’ temperatures remain at or below minus 240 degrees Fahrenheit (minus 151 degrees Celsius), they become cold traps, areas where water ice can accumulate and stay for extended periods of time.
Because of Ceres’ distance from the Sun, about 257 million miles (414 million kilometers), scientists expected the small world to have cold traps, but this is the first time the features have actually been identified.
Norbert Schorghofer of the University of Hawaii at Manoa and a guest investigator for the Dawn mission, along with a team of scientists, combined various images of Ceres captured by Dawn to create a three-dimensional image revealing its shape, craters, plains, and other features.
They used photos of Ceres’ northern hemisphere because it has been better lit by the Sun during the mission than the southern hemisphere and, therefore, has yielded better data.
After creating the three-dimensional image, the researchers inputted it into a NASA Goddard Space Flight Center computer model for analysis of the interaction between solar radiation and the dwarf planet’s surface.
The model determined which areas on Ceres’ northern hemisphere receive direct sunlight, the amount of sunlight that reaches the surface, and changes in these conditions throughout Ceres’ orbital period, which is 1,682 Earth days.
Schorghofer noted, “The conditions on Ceres are right for accumulating deposits of water ice. Ceres has just enough mass to hold onto water molecules, and the permanently shadowed regions we identified are extremely cold—colder than most that exist on the Moon or Mercury.”
The computer model identified many areas in Ceres’ northern hemisphere that are in permanent shadow and, therefore, likely to be cold traps.
A total of 695 square miles (1,800 square kilometers), less than one percent of the total surface area of the northern hemisphere, is permanently shadowed. The largest single shadowed region is located inside a crater 10 miles (16 kilometers) wide, slightly under 40 miles (65 kilometers) from the dwarf planet’s north pole.
Cold traps exist on Mercury and on the Moon, but only near the poles. On Ceres, which is further from the Sun, cold traps can extend to lower latitudes in the northern hemisphere.
The team’s findings have been published in the journal Geophysical Research Letters.
Video Courtesy of NASA/JPL-Caltech
Ceres’ permanently shadowed areas are likely colder than those on both Mercury and the Moon because at Ceres’ distance from the Sun, these areas do not even receive much indirect solar radiation.
“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,” said Dawn guest investigator Erwan Mazarico.
In terms of cold traps, Ceres is similar to Mercury, both in terms of the percentage of permanently shadowed regions and in terms of the ability to accumulate water ice, a condition known as trapping efficiency.
Ceres may have formed with a much larger reservoir of water than Mercury or the Moon, explained Dawn principal investigator Chris Russell of the University of California at Los Angeles.
“Some observations indicate Ceres may be a volatile-rich world that is not dependent on current-day external sources,” Russell said.
In the course of one Ceres year, approximately one out of every 1,000 water molecules generated on the dwarf planet’s surface will find its way to a cold trap. Over a period of 100,000 years, that is sufficient to form detectable surface ice deposits.
Laurel Kornfeld
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.
