Ceres is a unique body in the Solar System, bearing many similarities to Jupiter's moon Europa and Saturn's moon Enceladus, both considered to be potential sources for harboring life. In March of 2015, NASA's Dawn mission will arrive at the dwarf planet Ceres, the first of the smaller class of planets to be discovered and the closest to Earth.
When Ceres was discovered in 1801, astronomers first classified it as a planet. The massive body traveled between Mars and Jupiter, where scientists had mathematically predicted a planet should lie. Further observations revealed that a number of small bodies littered the region, and Ceres was downgraded to just another asteroid within the asteroid belt. It wasn't until Pluto was classified as a dwarf planet in 2006 that Ceres was upgraded to the same level.
Ceres is the most massive body in the asteroid belt, and larger than some of the icy moons scientists consider ideal for hosting life. It is twice the size of Enceladus, Saturn's geyser-spouting moon that may hide liquid water beneath its surface.
Unlike other asteroids, the Texas-sized Ceres has a perfectly rounded shape that hints toward its origins. 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. In August and October of 2013, NASA team members hosted a Google+ Hangout to discuss the upcoming visit to the nearest dwarf planet in the solar system. Parts 1 and 11 of this fascinating discussion follow.
"The fact that Ceres is so round tells us that it almost certainly had to form in the early solar system," Schmidt said. She explained that a later formation would have created a less rounded shape. The shape of the dwarf planet, combined with its size and total mass, reveal a body of incredibly low density.
"Underneath this dusty, dirty, clay-type surface, we think that Ceres might be icy," Schmidt said. "It could potentially have had an ocean at one point in its history."
"The difference between Ceres and other icy bodies [in the Solar System] is that it's the closest to the Sun," Castillo-Rogez said.
Less than three times as far as Earth from the Sun, Ceres is close enough to feel the warmth of the star, allowing ice to melt and reform. Investigating the interior of the dwarf planet could provide insight into the early solar system, especially locations where water and other volatiles might have existed.
As large as Ceres is, its distance has made it a challenge to study from Earth. Images taken by the space-based Hubble Space Telescope provided some insight to its surface, but to be sighted, features could be no larger than 25 kilometers in diameter. Several round circular spots mar the terrain, features which Schmidt said could be any one of a number of geologic terrains, including potentially impact basins or chaos terrains similar to those found on Europa. The largest of these, named Piazzi in honor of the dwarf planet's discoverer, has a diameter of about 250 kilometers. If this feature is an impact basin, it would have been formed by an object approximately 25 km in size.
But for Schmidt, this is another possible indication about the dwarf planet's surface: "It doesn't mean that Ceres hasn't been hit by something bigger than 25 kilometers," she said."It just means that whatever is going on on Ceres has totally erased [the topographic signature of that event]."
Ceres may have suffered major impacts, especially during periods of heavy bombardment early in the Solar System's history. If the surface contained ice, however, those features may have been erased.
"The spectrum is telling you that water has been involved in the creation of materials on the surface," Schmidt said.
The spectrum indicates that water is bound up in the material on the surface of Ceres, forming a clay. Schmidt compared it to the recent talk of minerals found by NASA's Curiosity on the surface of Mars. "[Water is] literally bathing the surface of Ceres," she said.
In addition, astronomers have found evidence of carbonates, minerals that form in a process involving water and heat. Carbonates are often produced by living processes.
The original material formed with Ceres has mixed with impacting material over the last 4.5 billion years, creating what Schmidt calls "this mixture of water-rich materials that we find on habitable planets like the Earth and potentially habitable planets like Mars."
Water is considered a necessary ingredient for the evolution of life as we know it. Planets that may have once contained water, such as Mars, as well as moons that could contain it today, like Enceladus and Europa, are all thought to be ideal for hosting or having once hosted life.
Because of its size and closeness, Schmidt calls Ceres "arguably more interesting than some of these icy satellites. If it's icy, it had to have an ocean at some point in time," she said.
Castillo-Rogez compared Earth, Europa, and Ceres, and found that the dwarf planet bore many similarities to Earth, perhaps more than Jupiter's icy moon. Both Earth and Ceres use the Sun as a key heat source, while Europa takes its heat from its tidal interaction with Jupiter. In addition, the surface temperature of the dwarf planet averages 130 to 200 degrees Kelvin, compared to Earth's 300 K, while Europa is a frosty 50 to 110 K.
"At least at the equator where the surface is warmer, Ceres could have preserved a liquid of sorts," Castillo-Rogez said.
Liquid water could exist at other points on the dwarf planet known as cold traps, shadowed areas where frozen water could remain on the surface. Such icy puddles have been found on Earth's moon.
"The chemistry, thermal activity, the heat source, and the prospect for convection within the ice shell are the key ones that make us think that Ceres could have been habitable at least at some point in its history," Castillo-Rogez said.
As scientists develop more information about Europa and Enceladus, there has been a greater call to investigate the two prime sites for life. But Schmidt and Castillo-Rogez think that Ceres could also be a great boon for astrobiology and space exploration.
"It's not a difficult environment to investigate," she said."As we think about the future of landed missions for people and rovers, why not go to Ceres?"
Though it would be more challenging to drill into than Europa, which boasts an icy surface layer, the dwarf planet would make a great site to rove around on. Schmidt also noted that it could make a great launching point when it comes to reaching the outer solar system. Its smaller mass would make it easier to land on--and leave--than Mars, which could make it a good site for manned missions.
"We have such a big planet bias, we have such a bias for things that look exactly like us," Schmidt said. "In this kind of special place in the Solar System, we have a very unique object that might be telling us a lot about what we don't know about building a habitable planet."
"I think when we get to Ceres, it's just going to be an absolute game changer, a new window into the Solar System that we wouldn't have without going there," Schmidt said
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, 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."
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 colors more or less the same, and reflecting very little light at all," said Andy Rivkin of the Johns Hopkins University Applied Physics Lab.
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 image below shows the 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."
NASA’s Dawn spacecraft has just returned the sharpest images ever seen of the dwarf planet Ceres shown above. The images were taken 147,000 miles (237,000 kilometers) from Ceres on Jan. 25, and represent a new milestone for a spacecraft that soon will become the first human-made probe to visit a dwarf planet.
"We know so little about our vast solar system, but thanks to economical missions like Dawn, those mysteries are being solved," said Jim Green, Planetary Science Division Director at NASA Headquarters in Washington.
At 43 pixels wide, the new images are more than 30 percent higher in resolution than those taken by NASA's Hubble Space Telescope in 2003 and 2004 at a distance of over 150 million miles. The resolution is higher because Dawn is traveling through the solar system to Ceres, while Hubble remains fixed in Earth orbit. The new Dawn images come on the heels of initial navigation images taken Jan. 13 that reveal a white spot on the dwarf planet and the suggestion of craters. Hubble images also had glimpsed a white spot on the dwarf planet, but its nature is still unknown.
Zoomed out -- PIA19173 Ceres appears sharper than ever at 43 pixels across, a higher resolution than images of Ceres taken by the NASA's Hubble Space Telescope in 2003 and 2004.
As the spacecraft gets closer to Ceres, its camera will return even better images. On March 6, Dawn will enter into orbit around Ceres to capture detailed images and measure variations in light reflected from Ceres, which should reveal the planet’s surface composition.
"We are already seeing areas and details on Ceres popping out that had not been seen before. For instance, there are several dark features in the southern hemisphere that might be craters within a region that is darker overall," said Carol Raymond, deputy principal investigator of the Dawn mission at JPL. "Data from this mission will revolutionize our understanding of this unique body. Ceres is showing us tantalizing features that are whetting our appetite for the detailed exploration to come."
Originally described as a planet, Ceres was later categorized as an asteroid, and then reclassified as a dwarf planet in 2006. The mysterious world was discovered in 1801 by astronomer Giuseppe Piazzi, who named the object for the Roman goddess of agriculture, grain crops, fertility and motherly relationships.
“You may not realize that the word ‘cereal’ comes from the name Ceres. Perhaps you already connected with the dwarf planet at breakfast today," said JPL's Marc Rayman, Mission Director and Chief Engineer of the Dawn mission.
Powered by a uniquely capable ion propulsion system, Dawn also orbited and explored Vesta, the second most massive body in the asteroid belt. From 2011 to 2012, Dawn returned more than 30,000 images, 18 million light measurements and other scientific data about the impressive large asteroid. Vesta has a diameter of about 326 miles (525 kilometers).
"With the help of Dawn and other missions, we are continually adding to our understanding of how the solar system began and how the planets were formed,” said Chris Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles.
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