Ceres' mystery spots are dimming, brightening daily

Ceres' bright spots entertained astronomers and enthusiasts for most of 2015, but ultimately ended as we'd expected all along — all signs point toward them being shiny salt patches reflecting the sun's light. Enter 2016 and a new plot twist no one anticipated — the dwarf planet's bright spots are randomly changing in intensity, growing brighter and dimmer throughout the day in a way that doesn't fully line up with the planet's rotation.

The Ceres bright spots were first photographed early last year by NASA's Dawn spacecraft, and we got increasingly better looks at them as Dawn flew closer. A few months into the trip, it became clear the bright spots were composed of much smaller bright spots collected together within craters, seemingly forming much larger spots when observed from a distance.

Researchers guessed from the start that ice or salt was responsible for the spots, eventually finding toward the end of last year that magnesium sulfate is responsible — they're essentially some craters filled with bath salts that catch the sun's light and reflect it back like shiny mirrors.

Using the ESO's HARPS instrument, researchers have come up with a way to accurately measure the Doppler shifts in light from the dwarf planet — and in doing so, they found the shifts in light. The plot twist, though, is that the light changes don't correspond quite right with how fast Ceres is rotating, meaning the shifts in light are likely caused by something changing on the planet's surface.

The most likely cause is ice within the bright craters being vaporized by the sun during the day, changing the nature of the light; later at night, the change in light and temp will diminish the haze. Researchers are only guessing about the cause at this point, basing their conclusion partly on past observations made by Dawn; a definite answer is not available at this time.