Mark January 26 on your calendar. It’s the day when the Dawn spacecraft will take images of Ceres that should exceed the resolution of the Hubble Space Telescope. We’re moving into that new world discovery phase that is so reminiscent of the Voyager images, which kept re-writing our textbooks on the outer Solar System. 2015 will be a good year for such, with Dawn being captured by Ceres gravity on March 6, and New Horizons slated for a July flyby of Pluto/Charon. In both cases, we will be seeing surfaces features never before observed.

What we have so far from Dawn can’t match earlier Hubble imagery, the best of which is about ten years old, but it’s about three times better than the calibration images taken by the spacecraft in early December. At this point, Dawn is making a series of images to be used for navigation purposes during the approach to the dwarf planet. We have sixteen months of close study of Ceres to look forward to as the excitement builds. “Already,” says Andreas Nathues, lead investigator for the framing camera team at the Max Planck Institute for Solar System Research, Gottingen, “the [latest] images hint at first surface structures such as craters.”

Image: An animated GIF showing bright and dark features on Ceres. The Dawn spacecraft observed Ceres for an hour on Jan. 13, 2015, from a distance of 383,000 kilometers. A little more than half of its surface was observed at a resolution of 27 pixels. Credit: NASA/JPL.

No spacecraft has ever visited a dwarf planet, another first for Dawn, which will also become the first spacecraft to have orbited two deep space destinations following its 2011-2012 sojourn at Vesta, where it produced over 30,000 images. Jian-Yang Li (Planetary Science Institute), who led the Hubble mapping of Ceres, says that even the early observations will be significant:

“Reproducing the Hubble observations is important to understanding the nature of Ceres’ surface. The recent detection of episodic water vapor near Ceres’ surface by the Herschel Space Observatory at a longitude observed by Dawn might arise from activity that could change Ceres’ surface over time.”

That discovery, relying on data taken in 2012, took advantage of the HIFI instrument on Herschel, which showed water vapor being emitted from the surface of Ceres, an early indication that Ceres has an icy surface and an atmosphere. Variations in the water signal during the dwarf planet’s nine hour rotation period helped Herschel scientists trace the water vapor to two spots on the surface. The two emitting regions are about five percent darker than the rest of Ceres, likely warmer regions that provide efficient sublimation of small reservoirs of water ice. In very short order, thanks to the Dawn spacecraft, we will be able to observe such features in dazzling detail.

For more on the Herschel work, see Küppers et al., “Localized sources of water vapour on the dwarf planet (1) Ceres,” Nature 505 (23 January 2014), 525–527 (abstract).