NASA DAWN: Ice on Ceres is an 'Interesting Paradox'

Hubble Space Telescope imaged the asteroid Vesta and the dwarf planet Ceres in 2007, both targets of NASA's Dawn mission. 

Credit: NASA, ESA, J. Parker (SwRI), L. McFadden (U Maryland)

As NASA's Dawn mission draws closer to its encounter with the dwarf planet Ceres in early 2015, excitement continues to mount for scientists looking forward to what the satellite might observe.

Britney Schmidt

Britney Schmidt, of the George Institute of Technology, and Nicole Gugliucci of CosmoQuest, recently hosted a Google+ Hangout titled 'Ceres: Great Expectations' to discuss the upcoming visit to the nearest dwarf planet in the solar system.

Orbiting in the asteroid belt, a little more than three times as far from the Sun as Earth, Ceres is thought to contain an icy mantle that makes up approximately a third of its mass.

"Ceres is very different and very exciting in a lot of ways, totally different from any place that we've been," Schmidt said in the broadcast. "It may be the only primarily icy planet that's out there, at least within reach."

Scratching the surface
Seen through a telescope, Ceres may not appear very exciting.

Scientists can use the light reflected off of a body to find out information about its composition.

"Ceres, to the eye, would appear basically pretty black because it's reflecting most colours more or less the same, and reflecting very little light at all," said Andy Rivkin of the Johns Hopkins University Applied Physics Lab.

Andy Rivkin

Even the infrared spectrum, which tends to reveal more information about asteroids such as Vesta—Dawn's first stop—provided very little information about its composition.

By utilizing instruments such as the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea in Hawaii, scientists were able to catch hints about the dwarf planet's surface.

These observations revealed suggestions of brucite, hydroxyls, and two other features Rivkin says are thought to be due to carbonate minerals.

"[This] makes Ceres one of only a few places where we've found carbonates," Rivkin said. "I think other than Earth and Mars, it's Ceres."

He went on to explain that scientists think water interacting with the minerals formed the brucite and the carbonates.

The layers of Ceres. Scientists think that the dwarf planet contains a rocky inner core surrounded by a thick mantle of water-ice. 

A thin outer crust covers the surface, with carbonates and other signs that water lay on the planet's skin at some point. 

Credit: NASA, ESA, and A. Feild (STScI)

"For Ceres, we think it is much more consistent with a body that had a lot of water available to interact with."

But water, considered a potential habitat for life to start, can't exist on the surface of the dwarf planet in either solid or liquid form.

"We see no real evidence for ice at the surface of Ceres," Rivkin said, noting that the dwarf planet is too warm. "However, conditions beneath Ceres' surface should allow buried ice to remain there."

At the same time, observations from the Hubble Space Telescope, as well as theoretical data such as the planet's density, suggest that a large amount of ice exists.

"That creates this interesting paradox. We think there's a lot of ice there, (but) we don't see any at the surface," Rivkin said.

"How that's going to translate into what we find when we show up there is still very much an open question."