NASA’s Dawn spacecraft is about to become history’s first mission to visit a dwarf planet, and it’s being greeted by “bright spots” on Ceres‘ surface that truly have “no analog in the Solar System,” Prof. Chris Russell, principal investigator for the Dawn mission, based at the University of California, Los Angeles, told AmericaSpace exclusively. It achieves orbit this Friday, March 6.
The science team is simultaneously “tremendously excited” by the “bright spots on Ceres” as well “totally surprised” and “frustrated” because it could take many weeks, months, or more to unravel the mystery.
The spots might be composed of highly some reflective materials like deposits of ice or salts since water accounts for about a quarter of Ceres composition. There has been much speculation whether they may be ice volcanoes or a result of cyrovolcanism.
I asked Russell if there are any analogs elsewhere in the Solar System like these bright spots on Ceres’ surface, especially like the newly discovered adjacent pair of spots seen inside an equatorial crater in images taken on Feb. 19?
“There is no analog to this visual phenomena in the solar system,” Russell told AmericaSpace.
“When we understand it better we may find an analog that displays itself differently. But this is a total surprise. Right now it seems to be unique!”
NASA released new images today (March 2) that were taken on Feb. 25 from a distance of about 25,000 miles (40,000 kilometers). Ceres appears half in shadow because of the current position of the spacecraft relative to the dwarf planet and the Sun. Soon there won’t be any new images taken again until mid-April, when it reaches its initial science orbit, with Dawn being on the dark side of Ceres in the meantime.
The history-making arrival of Dawn at Ceres is slated to take place later this week, if all goes well. And it’s staying for a very long time, not just a brief flyby encounter.
“Dawn is about to make history,” said Robert Mase, project manager for the Dawn mission at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., at a media briefing today, March 2.
“It will be captured into orbit at 4:20 a.m. PST [7:20 a.m. EST, 1220 GMT] on Friday, March 6. Our team is ready and eager to find out what Ceres has in store for us.”
But Dawn won’t be communicating with Earth at the time of capture. So the team will have to wait a few more hours for confirmation. Nevertheless, since no dramatic braking burns are required, it will literally be an uneventful event as Dawn is set to simply be captured into orbit by Ceres natural gravitational influence.
Although Ceres has been reclassified as a “dwarf planet,” the Dawn team regards it more as simply a planet.
“Ceres is a giant world,” said Mase. “It’s almost 600 miles (950 kilometers) wide.”
In fact Ceres measures about the size of Texas. It is the largest and most massive object in the main Asteroid Belt, which lies between Mars and Jupiter.
“Dawn will do big science on a small budget,” Mase stated. The overall mission cost is $473 million.
Video Caption: The surface of Ceres is covered with craters of many shapes and sizes, as seen in this new animation of a map of the dwarf planet’s surface. To make this animation, a map of Ceres, comprised of images captured by NASA’s Dawn spacecraft on Feb. 19, 2015, from a distance of nearly 29,000 miles (46,000 kilometers), was projected onto a globe. Ceres’ actual rotation is much slower; it takes about nine hours. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Ceres is providing scientists with plenty of perplexing puzzles, chiefly in the form of the utterly mysterious “bright spots.”
The two very brightest spots look like a pair of “eyes” and are located in a crater that’s about 92 kilometers (57 miles) wide. The spot in the center of the crater is about twice as bright as the other one.
“This extreme brightness was really unexpected. These spots were extremely surprising to the team. We are struggling to understand them,” said Carol Raymond, deputy project scientist at JPL. “The feature is unique in the solar system. The true nature is not yet known. They have been puzzling to the team and to everybody who’s seen them.”
“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 got us on the edge of our seats.”
“We know that Ceres retained a lot of volatiles and its shape is consistent with a differentiation into a rocky core and an ice mantle. So it’s inevitable that that ice would have existed as an ocean at some time in the past.”
Have any changes been detected on Ceres’ surface in all the images taken to date?
“We have not seen any changes on the surface in the images taken thus far,” Raymond told AmericaSpace.
Are the bright spots confined to being inside craters?
“The very brightest spots are located inside a crater. There are some other bright regions that show rayed structures emanating from a central crater and some that are not connected to a crater. So there are some features that show brightness variations but none as bright as the two very bright spots within the crater.”
The final approach phase began in December 2014. Since late January, Dawn’s images of Ceres have exceeded the resolution of those taken by NASA’s Hubble Space Telescope back in 2003 and 2004.
“I’m delighted that Dawn is on the doorstep of Ceres,” said Jim Green, director of NASA’s Planetary Science Division at the agency’s Headquarters in Washington, at the media briefing.
Scientists believe that Ceres may harbor an ocean of subsurface liquid water as large in volume as the oceans of Earth below a thick icy mantle, despite its small size, and thus could be a potential abode for life. Overall, Ceres is estimated to be about 25 percent water by mass.
Dawn’s images reveal Ceres to be a pockmarked world with craters of many sizes.
One of the largest craters looks somewhat like a pancake, or perhaps a sand dollar. The huge basin located south of the equator spans nearly 186 miles (300 kilometers) across and features a shallow interior, faint rim, and low-relief mounds.
Can you elaborate more on what the science team is thinking now about the bright spots, as Dawn has gotten closer and closer? Are they more or less likely to be ice volcanoes? I asked Russell.
“If you ask yourself what is different about Ceres you immediately think of its low density which implies a high (in this case 25 percent) percentage by mass of water,” Russell replied.
“If the body is 25 percent water, then how is it stored? Wet rock? Well, certainly some of that. Ice? Well, it is cold enough on the outside of Ceres to form ice. Liquid water? That is the main question mark. Is there a level with liquid water in it?”
How do the two bright spots compare to other bright regions on Ceres?
“No other region approaches the brightness of these two points.”
“Since there are a lot of craters, it may not be too surprising that this activity is in a crater. When we understand the physical cause of the bright spots we may then understand if the association with the crater is incidental or causative,” said Russell.
Dawn will soon make history as the first spacecraft to orbit two celestial bodies beyond Earth.
Dawn first visited Vesta, the second most massive asteroid in the main belt, for a year in 2011 and 2012. Vesta has an average diameter of 326 miles (525 kilometers).
The solar-powered mission was only enabled by the use of very efficient ion propulsion using xenon gas as propellant. Visiting two objects was not possible using only chemical thrusters, which are only about one-tenth as efficient.
After achieving orbit, Dawn will slowly spiral in to reach its initial science altitude orbit of about 8,400 miles (13,500 kilometers) in mid-April.
The mission is scheduled to last about 16 months, until June 2016.
Eventually, Dawn will spiral down very close to Ceres to a final altitude of about 235 miles (378 km) for its highest-resolution observations.
The mission duration is ultimately limited by the amount of hydrazine fuel on board. At the end of its useful life, “it will remain stable and stay in its lowest science orbit for hundreds of years,” said Mase.
“Studying Ceres allows us to do historical research in space, opening a window into the earliest chapter in the history of our solar system,” said Green. “Data returned from Dawn could contribute significant breakthroughs in our understanding of how the solar system formed.”
“Dawn is not an acronym. Dawn really refers to what the mission is all about, and that is going back in time and visiting the basic remnants of objects that come together to form our planets and what they are made of.”
Stay tuned here for continuing updates on Dawns’ orbital capture and science mission at protoplanet Ceres!
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Learn more about Dawn, MMS, Mars rovers, Orion, SpaceX, Antares, NASA missions and more at Ken’s upcoming outreach events:
Mar 6: “Dawn & MMS Update, Future of NASA Human Spaceflight, Curiosity on Mars,” Delaware Valley Astronomers Assoc (DVAA), Radnor, PA, 8 PM