Ceres -- the other dwarf planet humankind visited this year -- remains vexingly mysterious. NASA's Dawn orbiter first spotted the planet's strange bright spots months ago, and we've been itching to know what they're made of ever since.
Earlier in July, Dawn principal investigator Christopher Russell of the University of California at Los Angeles told The Washington Post that the favorite theory -- that the bright spots on Ceres, now known to be quite numerous, were made of some kind of ice -- was probably about to be debunked, and that spectral data suggested the spots were probably salt plains.
But it turns out that it won't be so easy to eliminate ice from the list of possibilities: Nature Magazine reports that Russell and his team have now spotted signs of an occasional haze above the crater housing the bright spots.
The haze, Russell told Nature, “could be providing some atmosphere in this particular region of Ceres." The haze isn't present everywhere they've seen bright spots, but it does seem to appear periodically over the large crater where bright spots were first seen. It could be that the haze is formed by sublimating ice, which would suggest that the bright spots are indeed frozen water.
Sometime next month, Dawn will move into a closer orbit around Ceres -- just about 900 miles over the surface. Hopefully that closer orbit will allow the team to collect better images and spectral data, solving the mystery once and for all.