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Hunt for Dwarf Planet Ceres' Mysterious Water Begins

NASA's Dawn spacecraft is about to make its second and final stop during its exploration of the asteroid belt and it is already returning some stunning images that are creating more questions than answers.

NASA's Dawn spacecraft is about to make its second and final stop during its exploration of the asteroid belt and it is already returning some stunning images that are creating more questions than answers.

After leaving massive asteroid Vesta's orbit in 2012, Dawn has traveled through the asteroid belt that occupies the region between the orbits of Mars and Jupiter to rendezvous with 600 mile-wide dwarf planet Ceres - the first spacecraft ever to orbit two celestial bodies during its mission.

VIDEO: Pluto Flyby and Black Holes: Top Space Events for 2015

The probe will be captured by Ceres' gravity on Friday, March 6, and in the run-up to this highly anticipated event, the probe has been sending back increasingly detailed observations of the solar system's innermost dwarf planet that are already puzzling planetary scientists. One puzzle focuses on bright patches on the Cererian landscape - one of which is a particularly bright spot, with a dimmer partner, inside an impact crater.

Speaking during Monday's press conference at NASA's Jet Propulsion Laboratory in Pasadena, Calif., Dawn deputy project scientist Carol Raymond outlined some possibilities that may explain these strange features. As previously reported, one mechanism that could be creating the bright patches is cryovolcanism, where sub-surface ice is forced to the surface. But as Dawn's imagery becomes sharper by the day, this mechanism is looking less likely.

"A cryovolcano will likely result in a constructional feature," said Raymond. "So we'd expect to see a mounded feature on the surface - some sort of deposit around a central vent or a crack. In the case of this crater, what we can say is that the brightest spot is not associated with a ‘positive relief feature' - i.e. a mound or peak ... so a cryovolcano is not at the top of the list for that feature."

ANALYSIS: NASA Spacecraft Ready to Unlock Ceres' Mysteries

We'll have to wait until Dawn has completed its first science orbit (in late-April) so the probe's instrumentation can be better calibrated to understand just why these spots are so bright and, ultimately, understand their origin.

Although cryovolcanism may be looking less and less likely, the mystery of Ceres' water is one of most exciting unknowns on the minds of the Dawn team.

"One of the mysteries is that of liquid water," Dawn mission director and chief engineer Marc Rayman told Discovery News. "Are there sub-surface reservoirs of water - ponds or lakes or oceans? I think that's really exciting."

From observations and theoretical models, scientists have a pretty good idea that Ceres was a planet in the making in the early epochs of the solar system. It is composed of stratified material and from density models of the world, there are strong indications that there should be sub-surface reservoirs of water.

As Ceres isn't heated by the the tidal heating that Saturn's moon Enceladus or Jupiter's moon Europa experience and receives weak sunlight as its only heat source, it is most likely that if Ceres did have sub-surface liquid water reservoirs early in its history, they are likely now long frozen, unless interactions with minerals in the rocks produced salts to maintain a liquid state.

ANALYSIS: Dwarf Planet's Puzzling Landscape Snaps into View

The expectation that Dawn would see Ceres covered with ice was further bolstered last year when the ESA Herschel space telescope detected water vapor in the vicinity of Ceres. Although it wasn't a huge quantity, it did boost hopes that Ceres may be venting water vapor into space from its sub-surface reservoirs, in a similar (but more understated) manner to Enceladus' impressive south pole geysers. Another theory is that, by chance, Herschel may have spotted the after effects of a meteorite impact on Ceres that kicked up surface ice into space.

Before Dawn started its approach of Ceres, it seemed highly possible that Ceres was going to have more in common with Enceladus and Europa - two icy worlds with sub-surface oceans. As it turns out, as Ceres came into focus, its ancient cratered surface, as opposed to an ice-covered crust, came as a surprise.

"That was the biggest surprise I think for me and many of the team members - when we saw those craters we were like ‘Okay...'," Raymond told Discovery News. "The ice should be close to the surface, it flows. So something else is going on. There's lots of ideas as to how we can explain that but we're going to have to sharpen our pencils, do a lot of detailed models and we're going to need a little more insight from high-resolution data (from Dawn)."

ANALYSIS: Ceres' Mystery Bright Dots May Have Volcanic Origin

There is still a possibility that water vapor may be escaping from the dwarf planet, but Dawn's instrumentation isn't designed to specifically seek out venting regions. But through the use of its infrared spectrometer, Dawn may be able to detect the back-scattered light created by dust that is being blown into space by the venting water vapor. A "tenuous atmosphere about Ceres" may also be a possibility, according to Raymond.

"Since I have the meteorology background, I most want to know what's going on with the water vapor, maybe there's an atmospheric thing going on," Keri Bean, Dawn mission operations engineer, told Discovery News. "Dawn will give us an answer, one way or another. It may not be able to see it (the water vapor), but that will also be a clue. So it will be interesting to see what Dawn does."

Rather than answering any questions early in Dawn's Ceres encounter, it seems even more questions are popping up.

"The real excitement is, what does Ceres have to tell us? It's not a specific question; it's rather that this is a mysterious alien world that, for two centuries has just been this faint smudge of light," added Rayman. "Now we're finally getting this in-depth, richly detailed portrait. That's what I think is exciting.

"What questions is Ceres going to answer that we're not even smart enough to ask now?"

NEWS: Water Plume ‘Unequivocally' Detected at Dwarf Planet Ceres

Understanding how Ceres is storing its water, what mechanics are driving the possible water vapor (and a potential atmosphere) and, of course, whether ice is behind the mysterious bright spots, are just a few components of our desire to seek out whether Ceres is (or was) a place that life as we know it would consider to be habitable. Following the water in any solar system body ultimately has this aim - to search for niches where life may take hold beyond Earth.

"I really hope that we are going to be able to say something definitive about Ceres' habitability and the way we would get at that is by reading the record of the surface - it would provide us clues as to what was going on at this ancient water-rock interface," said Raymond. "It's the types of minerals and how they got to the surface and what kind of convection or mixing was going on within the interior."

Ceres rotates in this sped-up movie comprised of images taken by NASA's Dawn mission during its approach to the dwarf planet. The images were taken on Feb. 19, 2015, from a distance of nearly 29,000 miles (46,000 kilometers). Dawn observed Ceres for a full rotation of the dwarf planet, which lasts about nine hours. The images have a resolution of 2.5 miles (4 kilometers) per pixel.

The term "dwarf planet" wasn't defined until the infamous International Astronomical Union (IAU) vote in 2006, but this year, 9 years later, we are beginning to get our first ever close-up views of two of our solar system's most famous dwarf planets: Pluto and Ceres.

VIDEO: Pluto Flyby and Black Holes: Top Space Events for 2015

Currently spiraling in on Ceres, the innermost dwarf planet inhabiting the asteroid belt between the orbits of Mars and Jupiter, NASA's Dawn spacecraft is slowly revealing a cratered and complex world, details of which that have so far eluded even Hubble's powerful vision. Dawn is scheduled to make final orbital insertion around Ceres in March 2015 where it is destined to remain after its fuel runs out as a permanent human-made satellite of Ceres. A comparison image of the Hubble and Dawn views of Ceres is shown above.

ANALYSIS: NASA Spacecraft Ready to Unlock Ceres' Mysteries

But Dawn is just the first dwarf planet encounter of 2015. In July, NASA's New Horizons mission will flyby Pluto and its system of moons, exploring the mysterious Kuiper Belt. Between Hubble's blurry observations of Ceres and Pluto and this year's NASA encounters, many artists' impressions of these enigmatic worlds have guessed at what lies in store for our robotic explorers. But how do they measure up now we are beginning to see Ceres' and Pluto's surfaces?

This artist's impression of Ceres shows NASA's Dawn spacecraft in orbit around the dwarf planet. As opposed to an ice encrusted world, this visualization shows a cratered, moon-like surface.

NEWS: Tantalizing Detail Seen on Mysterious Dwarf Planet

Again with Dawn in view, this artist's impression shows an active Ceres complete with water vapor escaping from a possible sub-surface ocean. Water vapor was detected in the vicinity of Ceres by Hubble, so Dawn will be on the look-out for any trace of geysers venting water.

ANALYSIS: Water Plume 'Unequivocally' Detected at Dwarf Planet Ceres

As seen by Hubble from afar, curious white patches and possible variations in Ceres' surface composition can be seen. However, any detail in these images have so far prevented planetary scientists from fully understanding the dwarf planet's true nature.

NEWS: What is That Mysterious White Blob on Ceres?

But now, as Dawn fast approaches orbital insertion, we're being treated to a bounty of data that shows a possibly ancient, rocky surface. Those curious white patches originally spied by Hubble are also snapping into view -- but what are they? Theories abound, but they may be tentative signs of subsurface water escaping to space and freezing on the surface. These are all signs of cryovolcanism, a dynamic that may dominate dwarf planet surface morphology.

NEWS: Dwarf Planet's Puzzling Landscape Snaps into View

From afar, NASA's Dawn mission is able to watch Ceres rotate, as this series of observations on Feb. 4 shows.

ANALYSIS: Craters Pop as NASA’s Dawn Probe Approaches Ceres

As Dawn gets up-close and personal with Ceres, the drama in the outer solar system is only just beginning to unfold. After 9 years of flying toward Pluto, NASA's New Horizons mission has begun approach preparations for its flyby in July.

VIDEO: Pluto Getting Bigger in New Horizons Probe's Window

From ground-based and Hubble observations, there at tantalizing clues that this frozen world has a surprisingly dynamic surface with a thin atmosphere that changes during Pluto's 248 year orbit around the sun. In this artist's impression of New Horizons flying over Pluto, an atmosphere has been included with cryovolcanos -- the latter of which planetary scientists hope to confirm in July.

Pluto has a system of known moons, the largest of which, Charon, may be considered to be Pluto's binary partner. As Charon orbits Pluto, its powerful gravitational field tugs the dwarf planet off center, a dynamic that New Horizons has observed as it approaches.

ANALYSIS: NASA Probe Captures First Pluto Approach Photos

This artist's conception shows Pluto's moon Charon eclipsing the dwarf planet. Twice every orbit around the sun, each world eclipses the other.

NEWS: Tally-Ho on Targets for New Horizons After Pluto

When Hubble spies on Pluto, it can see the different shades of the dwarf planet's surface rotate. As shown here in these blotchy images, little detail is obvious, but large regions with differing albedo (reflectiveness) may reveal huge craters, vast plains or mountains. But until New Horizons gets close, these regions will remain a mystery.

In this digital illustration rendered from 3-D NASA data of Pluto, an attempt has been made at matching observations with possible surface features.

In July 2014, NASA's New Horizons looked ahead and spied its ultimate goal: Pluto and Charon. Although tiny pinpricks of light, the pair can be seen orbiting one another in a binary dance that shifts Pluto off center. Both masses actually orbit an invisible point in space, above Pluto's surface, known as the Pluto-Charon barycenter. These observations have increased calls for Pluto to be redefined (yet again) as a 'binary planet.'

MORE: Can We Call Pluto and Charon a 'Binary Planet' Yet?

Having spotted Charon months ago, New Horizons is now beginning to see Pluto's wider family of moons pop into view. Shown here are moons Nix (yellow diamond) and Hydra (orange diamond).

MORE: Pluto's Tiny Moons Spied by Incoming NASA Probe

Once NASA's New Horizons mission careens through the Pluto-Charon system, assuming it doesn't hit any debris on its way through, its mission in the Kuiper Belt has only just begun. Hubble is currently being used to identify possible icy targets

after

the spacecraft's Pluto encounter. Shown here is an artist's impression of another dwarf planet, Eris, that was discovered in 2005. Originally thought to be the

tenth

planet of the solar system, its discovery led to the IAU's decision to reclassify these small worlds as dwarf planets, demoting Pluto in the process, leaving us with 8 planets. But as we approach Pluto and begin to understand Ceres, just because they are dwarf planets doesn't mean they're not rich and dynamic places to explore. Our voyage of dwarf planet discovery has only just begun and regardless of our need to classify celestial objects, Pluto and Ceres hold some fascinating clues to planetary formation and solar system evolution.

For more, regularly check on the

NASA Dawn

and

NASA New Horizons

mission web sites.