On Thursday, Science released a half-dozen papers that analyzed data the Dawn mission sent home from the largest body in the asteroid belt, a dwarf planet called Ceres. Headlines will focus on signs of water ice and a possible ice-powered volcano, but the reports themselves really end up emphasizing how much we still don't know about the strange world. Despite all of Dawn's imaging, many features don't add up to a coherent picture of the body as a whole.

Before Dawn got there, our impression of Ceres was dominated by what we'd measured of its density. Those measurements suggested the dwarf planet has a substantial amount of water and is large enough to have differentiated, allowing rocky material to sink to the core. So we expected Dawn to find an icy world where viscous ice has gradually wiped away many of the indications of the impacts every Solar System body has suffered.

That's not at all what Dawn found. Instead, only the largest impact craters on Ceres seem to show any sign of viscous changes. This lack of viscous change suggests that Ceres' crust is much more rigid than it would be if it were comprised of water ice.

Results from a paper published earlier this year (see sidebar) are confirmed and extended by one of the new papers in Thursday's Science. The new analysis also notes that many of the impacts created linear features nearby, which suggests that the crust was already fractured when the impacts occurred. This in turn suggests that "the near-surface crust must be both brittle enough to fracture and strong enough to retain fractures for long periods of time."

At the same time, the fact that some of the larger craters show signs of viscous deformation means that the crust can't be purely rock. And the shapes of the craters themselves also suggest that viscosity plays a key role while craters are forming. "Ceres' crust is weak (icelike) on the time scale of crater formation and modification," another paper concludes, "but relatively strong over longer, geologic time scales."

So, the papers mostly come to a compromise conclusion: the crust must be a mix of rock and ice. So, what's the rock? Examination of the surface composition reveals a lot of minerals called phyllosilicates. Different types of phyllosilicates have different chemical compositions, but they all share common structural features. On Ceres, the surface turns out to be a mixture of different types, with the composition showing large regional variation.

While those studies provide an overall picture of Ceres, two others look at unique features on the dwarf planet. One of these is the Oxo crater, which we know is a relatively young crater because there aren't many other craters inside it. Strikingly, imaging of the spectrum of light bouncing off the crater's surface shows signatures that are diagnostic of water being present. Given the conditions on Ceres, this would mean one of two things: either ice, or some mineral that incorporates water into its structure.

The authors looked at the spectra of various hydrated minerals, but they generally aren't great matches for the data from Ceres. Water ice, in contrast, is.

The problem with that is that water ice shouldn't be there for long. While the Oxo area is partly shielded from sunlight, conditions are such that the ice should vaporize away within decades. And, even if it didn't, dust would cover and obscure the ice relatively rapidly. So, the possible presence of ice indicates some sort of very recent activity on Ceres. The authors' list of possibilities include a landslide that exposed subsurface ice; release of water vapor followed by condensation on the surface; and eruption of an ice volcano.

Regardless of the cause, the authors note that the amount of time the ice would be visible after the event is so short that the odds of Dawn reaching Ceres at just the right moment to see the ice are very, very small. That's why they won't rule out hydrated minerals as a possible explanation.

The authors also note that Oxo is the only crater on the entire surface that shows a significant spectral signature of water, which leaves the significance of the discovery unclear. The same is true for a four-kilometer high peak called Ahuna Mons, which is the only feature of its sort—"distinct in its size, shape, and morphology"—on the dwarf planet.

Ahuna Mons sits at the edge of a slightly elevated bulge, next to a relatively recent impact crater. Its base is shaped like an ellipse, with one end rising above the rest. From a relatively smooth base, the terrain transitions into what looks like debris that slid down the slope a bit (called "talus"). Above that, the peak is jagged and complex, including a variety of ridges and fractures; it's also slightly bowl-shaped overall.

The authors note that this looks almost exactly like a stratovolcano on Earth. The fractures and ridges at the top indicate that there have been multiple peak-forming events, and excess material has fallen downslope to form the talus-covered areas. The authors propose that the nearby impact, which is slightly older than Ahuna Mons, probably opened a channel to the interior, where salty brines could be liquid at depths of 50 kilometers.

But again, Ceres is covered in craters, and Ahuna Mons is the only feature of its sort on the entire surface. And scientists hate to conclude too much from a sample size of one.

Dawn's time at Ceres has told us a huge amount about the surface of the dwarf planet, and the space probe has provided insights into some of the features that it found there. But, while it's told us that our expectations for Ceres were way off base, Dawn hasn't yet replaced those expectations with a coherent picture. So while we might be able to provide plausible explanations for some of the details, making sense of Ceres is not yet possible.

Science, 2016. DOI: 10.1126/science.aaf4286, 10.1126/science.aaf4759, 10.1126/science.aaf4332, 10.1126/science.aaf4279, 10.1126/science.aaf3010 (About DOIs).