Some of our smallest astronomical neighbors just keep getting odder and odder: recent observations of the bright spots found on dwarf planet Ceres have shown them to be brightening and dimming over the course of it’s 9-hour day.

The spots, made of a briny mixture containing magnesium sulfate hexahydrite, appears to be upwelling in certain spots from below the former asteroid’s surface. The spots have been found to emit a haze, indicating that the water in the material is evaporating into space, leaving the pale minerals deposited on Ceres’ dark surface.

Using the European Southern Observatory’s 3.6-metre ground-based telescope, Paulo Molaro of the INAF–Trieste Astronomical Observatory observed the brightest spots, located in Ceres’ Occator Crater, brightening an dimming over the course of the planetoid’s day. This correlates with the theory that the spots are formed from geysers, an indication of geological activity. Until recently, only Earth and Jupiter’s moon Io were the only bodies known to still be geologically active, with the surprise discovery of geological activity on Pluto being made by the New Horizons probe just early last year.

While the brightening of the spots is easy to explain — they’re simply being refreshed with new material from below the surface — the dimming, however, is another matter. Molaro theorizes that this is caused by some of the deposited minerals sublimating from the surface when the sun warms the deposits, transferring directly from a solid to a gas that escapes into space. If this theory is correct, this would also possibly contribute to the dim haze observed over the bright spots, a tenuous atmosphere on a tiny planet.