Ceres is a dwarf planet with a bizarre surface, marked by mysterious bright spots that have left astronomers perplexed. Now, these odd features appear to be changing over time, and scientists are left with no way to adequately explain the phenomenon.
The Dawn spacecraft was the first to reveal the presence of the bright spots, as the orbiting observatory arrived at the largest body in the asteroid belt in 2015.
One hypothesis to explain the changes is that sunlight falling on ice patches is converting the frozen areas into vapor. However, the changes seen by astronomers using ground-based telescopes do not appear to be timed with the day-night cycle of the dwarf planet.
The Occator crater on Ceres is home to the enigmatic markings. Dawn observations suggest that the white markings are likely composed of hydrated magnesium sulfates, commonly known as Epsom salt.
The rotational rate of Ceres may be measured from Earth by observing the Doppler shift of light reflected from its surface. Light coming from the edge turning toward Earth is shifted to the blue end of the spectrum, while the other side becomes red-shifted. However, surface features on the rocky body can also affect the light being reflected to Earth. By measuring this effect, astronomers believe they will be able to record changes on the surface of Ceres even after the end of the Dawn mission.
No earth-based telescope, including those in space, are able to discern details on the body orbiting between Mars and Jupiter. Even the mighty Hubble Telescope is unable to reveal distinctive markings on the object.
The High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at the La Silla Observatory in Chile was used to make the new measurements. Astronomers recorded data for two nights in July and August 2015.
"The result was a surprise. We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night," said Antonino Lanza from the INAF-Catania Astrophysical Observatory.
Astronomers theorize the process of freezing and vaporizing could take more than a day to complete. Such a mechanism could explain why the observed changes do not match the nine-hour rotational period of the dwarf planet.
Ceres is unlike other bodies in the asteroid belt, and the object is known to posses significant amounts of water. However, astronomers are uncertain whether this is related to the appearance of the strange markings.
Study of the newly-discovered changes in the bright spots of Ceres is detailed [pdf] in an article made available by the European Southern Observatory.
