"As soon as the Dawn spacecraft revealed the mysterious bright spots on the surface of Ceres, I immediately thought of the possible measurable effects from Earth," lead author Paolo Molaro of the INAF-Trieste Astronomical Observatory said in a statement. "As Ceres rotates the spots approach the Earth and then recede again, which affects the spectrum of the reflected sunlight arriving at Earth."
Molaro and his colleagues were surprised to see that the spot brightness fluctuated in a way they hadn't predicted, based on Ceres's orbit. "We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night," he said.
In July, overnight observations suggested that the spots were changing – perhaps because some of their components evaporated as the sun warmed the dwarf planet's surface. But observations made for the same amount of time in August saw no such changes.
The researchers need more data to figure out why that fluctuation occurs, but it could be that whatever process causes these spots to change takes more than a few days. If Ceres really is actively creating and evaporating some kind of ice, it means the cold little world is even cooler – and more geologically active – than anyone expected.
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Rachel Feltman runs The Post's Speaking of Science blog.