Pictures with a resolution previously unattained were taken during imaging sessions starting in January 2015 as "Dawn" approached Ceres, showing a cratered surface. Two distinct bright spots (or high-albedo features) inside a crater (different from the bright spots observed in earlier Hubble images) were seen in a 19 February 2015 image, leading to speculation about a possible cryovolcanic origin or outgassing. On 3 March 2015, a NASA spokesperson said the spots are consistent with highly reflective materials containing ice or salts, but that cryovolcanism is unlikely. However, on 2 September 2016, scientists from the Dawn team claimed in a "Science" paper that a massive cryovolcano called Ahuna Mons is the strongest evidence yet for the existence of these mysterious formations. On 11 May 2015, NASA released a higher-resolution image showing that, instead of one or two spots, there are actually several. On 9 December 2015, NASA scientists reported that the bright spots on Ceres may be related to a type of salt, particularly a form of brine containing magnesium sulfate hexahydrite (MgSO4·6H2O); the spots were also found to be associated with ammonia-rich clays. In June 2016, near-infrared spectra of these bright areas were found to be consistent with a large amount of sodium carbonate (), implying that recent geologic activity was probably involved in the creation of the bright spots. In July 2018, NASA released a comparison of physical features found on Ceres with similar ones present on Earth. From June to October 2018, "Dawn" orbited Ceres from as close as and as far away as . The "Dawn" mission ended on 1 November 2018 after the spacecraft ran out of fuel.