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This image of the dwarf planet Ceres, taken by NASA’s Dawn mission on February 19, 2015 from an altitude of 46,000 kilometers, reveals that a previously seen bright spot in a crater is actually two spots. The spots may be highly reflective ice or mineral deposits—or something even stranger.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Dawn Spacecraft Sees Spots as It Approaches Mysterious Ceres
Spectacular new images are trickling in from NASA’s mission to a dwarf planet in the Asteroid Belt
March 2, 2015 |By Lee Billings
The largest and most mysterious resident of the debris belt between Mars and Jupiter is an icy world called Ceres, and it’s on the threshold of being explored up close for the first time by NASA’s Dawn mission, which is scheduled to enter Ceres’s orbit on March 6.
Discovered in 1801 by the Italian astronomer Giuseppe Piazzi, Ceres was initially thought to be a full-fledged planet. That began to change when one of Piazzi’s rivals, the astronomer William Herschel, noted that Ceres only appeared as a point of light in his telescope rather than a resolved disk, like the other known planets. To Herschel that meant Ceres was probably too small to be considered a planet, and he coined the term “asteroid” to describe its starlike appearance. Ceres received a minor upgrade to “dwarf planet” in 2006, part of the same process that demoted Pluto to the same status.
Whatever you call may call it, Ceres is one of the most geologically interesting and strange objects in the solar system. Its shape, size and composition—round, roughly the size of Texas and at least 20 percent water ice—place it at the poorly understood transition point between rocky worlds like Earth and icy worlds like Jupiter’s Europa, Saturn’s Enceladus, and other large moons of the outer solar system. Other than blurry Hubble Space Telescope images from 2004, its surface had scarcely been glimpsed until Dawn’s approach. As the spacecraft’s ion engines slowly push it toward Ceres, the dwarf planet’s details are now coming into focus, revealing tantalizing new details with practically every new image.
>>View a slide show of the best images of Ceres
In the latest images, taken from 46,000 kilometers away and released on February 25, Dawn has sharpened its view of mysterious bright spots dotting Ceres’s crater-pocked surface, some of which were previously seen in the Hubble images. What used to appear as Ceres’s brightest blotch now appears to be two—a brighter, larger spot next to a smaller, dimmer one, both in the same crater. “Bright” is a relative term—all the bright spots are actually quite dark but still far brighter than the rest of Ceres, which is blacker than coal. No one knows what the bright spots are but guesses abound: Perhaps they are scars from recent impacts or minerals deposited by active geysers or water ice erupted by “cryovolcanoes”—or something even wilder. In 2014 the Herschel space telescope spied transient plumes of water vapor tentatively linked to the approximate locations of the white spots in Hubble images.
“Ceres’s bright spot can now be seen to have a companion of lesser brightness, but apparently in the same basin,” says Chris Russell, Dawn’s principal investigator, based at the University of California, Los Angeles. “This may be pointing to a volcanolike origin of the spots but we will have to wait for better resolution before we can make such geologic interpretations.”
“The images now are just at that intriguing resolution that lets you make stuff up,” says Mike Brown, the California Institute of Technology astronomer whose work helped motivate the reclassification of Pluto and Ceres as dwarf planets. The white spots would seem to be exposed ice, Brown says, but observations of Ceres with ground-based telescopes don’t show any evidence of ice at the bright spots’ locations.
But ice shouldn’t be stable at Ceres’s surface, says Andy Rivkin, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory. “So its presence there would mean it’s only gotten there recently, either by having impacts expose it or…. Well, probably that’s the only way,” Rivkin says. “I suppose cryovolcanism could also bring it to the surface, but impacts would be the safer bet.”
All anyone really knows for sure right now is that the spots are getting brighter as Dawn’s view sharpens, says Mark Sykes, director of the Planetary Science Institute and a Dawn mission scientist. And the brighter they become “the more interesting they get,” because water ice is one of the brightest things researchers could possibly see on Ceres. “If we discover something like cryovolcanism on Ceres, that would be spectacular because it would be an indicator that there are subsurface reservoirs of water,” Sykes says. “This isn’t what you normally think of as an asteroid, a dead potato just being smacked around by its neighbors out in space. There is a lot happening on this object, and that could make Ceres very astrobiologically important.”
If Ceres proves to be a possible home for extraterrestrial life and is venting water into space, Sykes says, “this raises the possibility that we could send another spacecraft there in the near future to go down to one of these spots, scoop up soil, take a look and ask whether there are any dead bugs in there.” Such a mission would be relatively inexpensive, Sykes says, because Ceres is so close by and accessible. “It’s between Mars and Jupiter, it’s not a nasty radiation environment like Jupiter’s Europa, it’s not really far away like Saturn’s Enceladus and it’s got low gravity so it doesn’t require lots of energy to land on! It’s too early to say whether this stuff is there, but the prospect is very exciting.”
Dawn is still in the earliest phases of investigating Ceres, and the best images and scientific data are yet to come. It will eventually swing down to within about 400 kilometers of the surface to study its composition and to generate high-resolution maps. The spacecraft will spend at least the next 16 months studying Ceres, but because the dwarf planet could potentially be an abode for subsurface life Dawn will not be crashed into it at the end of its life, as is the usual procedure. Instead, it will be left in orbit, becoming a long-lived mechanical moonlet of Ceres once its mission ends
Dawn Spacecraft Sees Spots as It Approaches Mysterious Ceres - Scientific American
NASA Spacecraft Making First Visit to Dwarf Planet Ceres
PASADENA, Calif. — Mar 2, 2015, 6:00 PM ET
By ALICIA CHANG AP Science Writer
A NASA spacecraft is about to reach the end of a nearly eight-year journey and make the first rendezvous with a dwarf planet.
The Dawn craft will slip into orbit Friday around Ceres, a dwarf planet the size of Texas. Unlike robotic landings or other orbit captures, the arrival won't be a nail-biter. Still, Dawn had to travel some 3 billion miles to reach the largest object in the asteroid belt between Mars and Jupiter.
"It's been a roller coaster ride. It's been extremely thrilling," project manager Robert Mase of the NASA Jet Propulsion Laboratory said Monday.
Ceres is the first of two dwarf planets to receive visitors this year. NASA's New Horizons spacecraft is barreling toward one-time planet Pluto where it will arrive in July. Dwarf planets are worlds that are spherical in shape. But unlike traditional planets, dwarf planets share the same space with other similar-sized celestial objects.
Launched in 2007, Dawn made the first stop of its journey at the asteroid Vesta. It beamed back more than 30,000 images of the rocky world inside the asteroid belt before heading to its final destination.
Dawn began its approach to Ceres in December, and last month it snapped pictures of the dwarf planet that revealed two mysterious bright spots inside a crater. Scientists will have to wait until the craft spirals closer to the surface in the coming months to get sharper images. It will get as close as 235 miles above Ceres' surface, or roughly the distance of the International Space Station above Earth.
Last year, European researchers not connected with the mission detected water plumes spewing from two regions on Ceres. The source of the plumes remains unclear.
Deputy project scientist Carol Raymond said the shiny patches — possibly exposed ice or salt — were a surprise and could be related to the plumes. Dawn carries an instrument that should be able to detect the plumes if the surface is still active.
"The team is really, really excited about this feature because it is unique in the solar system," Raymond said of the spots. "We will be revealing its true nature as we get closer and closer to the surface. So the mystery will be solved, but it is one that's really got us on the edge of our seats."
The $473 million Dawn mission is the first to target two different celestial objects to better understand how the solar system evolved. It's powered by ion propulsion engines, which provide gentle yet constant acceleration, making it more efficient than conventional rocket fuel. With its massive solar wings unfurled, it measures about 65 feet, the length of a tractor-trailer.
Vesta and Ceres reside in a zone between Mars and Jupiter that's littered with space rocks that never grew to be full-fledged planets.
The two are "literally fossils that we can investigate to really understand the processes that were going on" during the formation of the solar system, Raymond said.
Dawn entered orbit around Vesta in 2011 and spent a year photographing the lumpy surface and taking measurements of the second massive object in the asteroid belt from different altitudes.
Unlike rocky Vesta, Ceres — discovered in 1801 and measuring 600 miles across — is thought to possess a large amount of ice, and some scientists think there may have been an ocean lurking below the surface.
Dawn will study Ceres for 16 months. At the end of the mission, it will stay in the lowest orbit indefinitely, said Mase, adding that it could remain there for hundreds of years.
Scientists will get a glimpse of another icy dwarf planet this summer when New Horizons arrives at Pluto. Once considered the ninth planet, Pluto was demoted to dwarf planet in 2006, seven months after New Horizons was launched.
NASA Spacecraft Making First Visit to Dwarf Planet Ceres - ABC News
Bright spotlight on Dawn mission to Ceres
By Jonathan Amos BBC Science Correspondent
Scientists say they are hugely excited to learn the origin of two bright spots on the surface of Ceres.
The US space agency's Dawn probe is bearing down on the dwarf planet and on Friday will be captured by its gravity.
That will allow the satellite to spiral down in altitude in the coming months, to take ever sharper images of the spots, which sit inside a wide crater.
The striking features could be where an impact has dug out surface deposits and exposed the dwarf's interior layers.
But deputy project scientist Dr Carol Raymond cautioned that the resolution of Dawn's imagery was not good enough at the moment to make any definitive statements.
"These spots were extremely surprising and they have been puzzling to everyone who has seen them," the Nasa Jet Propulsion Laboratory researcher told reporters.
"They show up in a 92km-wide crater that's about 19 degrees North latitude. The spot in the centre is about twice as bright as the spot on the side of the crater, and as yet it has not been resolved, meaning it is smaller than the 4km pixel size [of the images].
"But its apparent brightness is already off-scale; it's consistent with high reflective materials."
Intriguingly, the European Space Agency's Herschel telescope reported last year seeing water vapour coming from two sectors on Ceres. One of these sectors includes the location of the spots. That could be very significant, Dr Raymond said.
"The association with the impact crater may indicate that impact heating resulted in exposure of underlying ice [and] its vaporisation; and perhaps we're seeing a deposit left behind which is rich in material like salts."
Dawn will spend 14 months studying the 950km-diameter dwarf planet, which is the largest object in the asteroid belt between Mars and Jupiter.
The satellite has turned up at Ceres having previously visited the asteroid Vesta. This 530km-wide rock had the look of a punctured football, the result of a colossal collision sometime in its past that ripped a big chunk out of its southern polar region.
Ceres, on the other hand, is big enough for gravity to have pulled it into a more spherical shape.
Scientists think both bodies are fledglings that never quite made it to the planetary big time.
In the case of Vesta, it underwent a lot of the same processes that transformed the early Earth, such as differentiating its insides to include an iron core.
In contrast, Ceres's bid to reach the major planet league probably stalled quite quickly.
Researchers believe its interior is dominated by a rocky core topped by ice that is then insulated by rocky lag deposits at the surface.
The surface of Ceres is covered with craters of many shapes and sizes
A big question the mission hopes to answer is whether there is a liquid ocean of water at depth. Some models suggest there could well be.
The evidence may well be found in Ceres' craters which have a very muted look about them. That is, the soft interior of the dwarf has undoubtedly had the effect of relaxing their original hard outline.
"One of the prime motivations of the Dawn mission is to examine these building blocks of the planets, Vesta and Ceres, which are two intact proto-planets from the very dawn of the Solar System. They're literally fossils that we can investigate to really understand the processes that were going on at that time," Dr Raymond said.
At capture, the satellite will be at a separation of about 40,000km. Controllers at Earth will work in the next few weeks to reshape the orbit to get it ready for science.
One issue is that Dawn approached the dwarf from its Sun-lit side. The probe has now gone over to the dark side, and it will not come back around again to take images until late April.
But then onwards, the pictures will just get better and better as the orbit is progressively lowered.
"We'll get to our final orbit in December of this year at just [380km] from the surface, which for context is just a little bit lower than the International Space Station orbits around the Earth. From this vantage point, Dawn will acquire its highest detail and highest resolution images of the surface," said Nasa project manager Robert Mase.
Discovered in 1801 by the Sicilian astronomer Father Giuseppe Piazzi, Ceres is named after the Roman goddess of agriculture and harvests.
Craters on Ceres will follow a similar theme and will be named after gods and goddesses of agriculture and vegetation from mythology. Other features on the dwarf will be named after agricultural festivals.
The soft outline of the big basin suggests that the surface has relaxed over time
BBC News - Bright spotlight on Dawn mission to Ceres
