"I think of Ceres actually as a game changer in the Solar System," said Britney Schmidt, science team liaison for the Dawn Mission. "Ceres is arguably the only one of its kind. "Ceres is like the gatekeeper to the history of water in the middle solar system."
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. InAugustand October 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.
NASA Ceres Team Discussion Part 1
"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."
NASA's Dawn mission launched September 27, 2007. It traveled to the asteroid Vesta, where it remained in orbit from July 2011 to July 2012 before heading to Ceres. It is slated to spend five months studying the dwarf planet, though Schmidt expressed hope that the craft would continue working beyond the nominal mission, allowing the team to study the icy body even longer.
Castillo-Rogez pointed out that not only will Dawn reach Ceres in 2015, the European Space Agency'sRosetta spacecraft will be escorting the comet Churyumov-Gerasimenko around the Sun that year, while NASA's New Horizons mission will be reaching Pluto and its moon Charon.
"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
NASA Ceres Team Discussion Part 11
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."
When Dawn arrived at Vesta in mid-2011, scientists already had a head start on what the spacecraft might find. That's because debris from the asteroid had split off and fallen to Earth in the form of meteorites some time ago.
Katie Dyl, of Curtin University in Australia, studies different types of meteorites in an effort to understand what the solar system was like in its earliest stages.
By comparing the composition of the meteorites in laboratories with asteroids in space, scientists are able to locate their sources.
"That's how we learned we have meteorites from Vesta," Dyl said. "People like Andy [Rivkin] measured spectra in space, and people like me took meteorites from the lab and measured their spectra, and they're exactly the same."
But scientists have yet to locate any samples that come from Ceres.
"We can't quite do that with Ceres yet," Dyl said. "That's why it's really interesting to actually go there and get a better look."
"We're pretty sure we don't have meteorites from Ceres itself, so we're missing that link that we had for Vesta to be able to put it all together," he said. "Dawn is really going into new territory in that sense."
But the spacecraft isn't flying completely blind. Although scientists don't have samples from Ceres, they are using other meteorites to garner insight into what the dwarf planet might contain.
Two competing theories suggest why carbonates lay on the dwarf planet's surface.
Meteorites from the asteroid Vesta have been found on the Earth's surface, but no such samples have been discovered from Ceres.
The first has to do with the early days of Ceres. Like full-sized planets, Ceres was once a collection of dust and gas orbiting the young Sun in a pancake-like disk. Gravity drew the different components together, and the collection grew into the dwarf planet. (Were it not for the disrupting presence of Jupiter, Ceres might have continued growing into a full-scale planet.)
During its formation, the ice and rock separated, with the rocky crust sinking down through the ice and water. But Ceres lies too close to the Sun for ice to remain at its surface, especially near the equator, though it may continue to exist at the poles.
"That ice would then start to sublime away, and leave whatever was collected in the ice behind," Rivkin said — including the brucites and carbonates now seen on the surface.
The other option involves punctures in Ceres’ rocky crust due to impacts or natural stresses. Icy lava welling up to the surface would drag brucites and carbonates with it. When the ice sublimated, the materials themselves would be left behind.
"Hopefully we'll be able to determine which of those two is going on at Ceres," Rivkin said.
Dyl echoed his enthusiasm at Dawn's impending arrival.
"I can't wait to be astounded, because it's just kind of how every single step we take in space seems to go," she said. "We see something that we couldn't have predicted."
The Daily Galaxy via NASA Astrobio,net and Google Hangout
Image credits: NASA, ESA, and A. Feild (STScI)