Ever since they were first discovered in images sent back by NASA’s Dawn spacecraft last year, the mysterious bright spots on Ceres have fascinated space-science enthusiasts all over the world, and now new research has suggested that the odd features may be changing unexpectedly.
In research published in a recent issue of the Monthly Notices of the Royal Astronomical Society, Paolo Molaro from the INAF–Trieste Astronomical Observatory and his colleagues reported that they had detected unusual variations suggesting that the spots are made out of a volatile material that evaporates in sunlight, and that these changes are happening almost constantly.
According to Space.com and Popular Science, Molaro’s team used the HARPS spectrograph at the European Southern Observatory (ESO) 3.6-metre telescope at La Silla, Chile to observe the spots, and found that they were growing brighter during the daytime hours. That would seem to indicate that whatever these bright spots are made out of is vaporized by the heat of the sun.
Furthermore, they also found that the brightness of the spots varies from one day to the next, a discovery that appears to support the hypothesis that sunlight regularly changes ice into vapor in the Occator crater where the spots are located, the websites added. However, this change appears to be irregular and does not precisely follow the dwarf planet’s day-night cycle.
Presence of volatile substances the most likely explanation
Ceres spins on its axis once every nine hours, the researchers explained in a statement, and their calculations indicate that the effects due to the motion of the spot as it moves closer to or further away from Earth would be relatively small. However, the motion is large enough that they were able to measure it using the HARPS spectrograph during a two-night span last summer.
“The result was a surprise,” said co-author Antonino Lanza of the INAF-Catania Astrophysical Observatory. “We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night.” Lanza, Molaro and their colleagues were able to determine that the observed chances were due to the presence of volatile substances in the bright spots that evaporated under the action of solar radiation.
When the bright spots within Occator crater are exposed directly to the sun, they form plumes that reflect sunlight, the researchers explained. These plumes quickly evaporate, lose reflectivity, and produce the changes detected by the HARPS spectrograph. The effect changes from one night to the next, however, leading to additional random patterns both during the short term and over a longer period of time.
“If this interpretation is confirmed Ceres would seem to be very different from Vesta and the other main belt asteroids,” the ESO explained. “Despite being relatively isolated, it seems to be internally active. Ceres is known to be rich in water, but it is unclear whether this is related to the bright spots. The energy source that drives this continual leakage of material from the surface is also unknown.”
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Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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