An image captured by the Dawn spacecraft showing Ceres' northern hemisphere being illuminated by Sun. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Heightened solar activity may be responsible for the creation of a transient, temporary atmosphere on dwarf planet Ceres, say NASA Dawn mission scientists.
Ceres is the largest object in the asteroid belt, which lies between Mars and Jupiter.
Before NASA’s Dawn spacecraft arrived in orbit to study Ceres in 2015, evidence for an atmosphere at the dwarf planet had already been mounting, but it seemed that the atmosphere was only there sometimes.
It is now thought that energetic particles from the Sun are hitting exposed ice and also ice near the surface of Ceres, causing the water particles to escape and create an atmosphere that lasts about a week.
When Dawn began its study of Ceres in March 2015, NASA scientists found evidence for ice water, leading to the theory that the dwarf planet’s atmosphere is generated by ice sublimating into water vapour.
This would occur as Ceres gets closer to the Sun, causing more water vapour to be released and creating the temporary atmosphere.
But the new study shows that the creation of the atmosphere is actually related to the Sun’s activity, rather than Ceres’ proximity.
"Sublimation probably is present, but we don't think it's significant enough to produce the amount of exosphere that we're seeing," says Michaela Villarreal, lead author of the new study and a researcher at the University of California.
The study scientists showed that past detections of the atmosphere were related to higher concentrations of energetic protons being ejected by the Sun, and also that some of the strongest detections of Ceres’ atmosphere did not actually occur during its close approach.
"Our results also have implications for other airless, water-rich bodies of the solar system, including the polar regions of the moon and some asteroids," says Chris Russell, principal investigator of the Dawn mission.
"Atmospheric releases might be expected from their surfaces, too, when solar activity erupts."