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In December 2003, the Hubble Telescope spotted something peculiar on the surface of Ceres, a dwarf planet in the asteroid belt between Mars and Jupiter. Hazy images revealed something bright and mysterious shining on the dark planet’s surface, like animal eyes in the night.
Marc Rayman, a physicist and engineer at NASA’s Jet Propulsion Laboratory, studied the images.
A Hubble image of Ceres in 2003. Image by NASA, ESA and J. Parker
It was hard to know what to make of them. With no other reference, a point of light in the dark could be a firefly at the end of the driveway or a brilliant star hundreds of light years away. Likewise, Rayman wondered, did this bright spot represent a large region on the planet’s surface? (Think variations on the moon.) Or was it a small, highly reflective area? The latter, he knew, would be more interesting.
Four years later, the Dawn spacecraft lifted off from the Cape Canaveral Air Force Base atop a Delta II rocket and soared into the sky. From wingtip to wingtip, the probe was nearly 65 feet, roughly the distance from pitcher’s mound to home plate — marking the greatest wingspan of any interplanetary spacecraft NASA had ever launched. It was headed for the asteroid belt, home to billions of rocky and metallic fragments.
For seven years and 3.1 billion miles it traveled, pausing on the way for a yearlong residency at the giant asteroid Vesta, where it captured breathtaking images of Grand Canyon-sized canyons and a mountain more than twice the height of Mount Everest. Finally, in January, it was close enough to point its camera at Ceres.
Dawn snapped its first deep space shot of Ceres on Jan. 13, 2015 and then turned its main antenna to Earth to beam back the data. That data was processed overnight, and Rayman spent the next morning refreshing his email, waiting for the images to appear.
THE PEOPLE THAT POWER THE SPACECRAFT
The Jet Propulsion Laboratory in Pasadena, Calif., where Rayman leads the Dawn mission team, sits at the foothills of the San Gabriel Mountains. Office windows there overlook the mountains, when they’re not obscured by fog. The sprawling facility is larger in square footage than Disneyland and designed like a college campus, with boxy buildings and courtyard coffee carts. Deer from the nearby hills wander in to share the grounds with humans, munching on spiky plants and the occasional stray potato chip. (“We like to joke that they’re robots,” said Preston Dyches, a communications specialist. “Robotic deer rovers.”)
The facility’s main mission control room is the nerve center for JPL’s Deep Space Network. In the dark room, computers flash data and lights. A big screen projects signals from deep-space probes like New Horizon, Dawn and the two Voyager spacecrafts, along with information on the multiple antennas in Spain, Australia and California that catch those signals.
Video by Justin Scuiletti
The Dawn mission team works a few buildings over. And for a group that deals in ion propulsion and xenon propellant, the headquarters are surprisingly understated. The team’s own mission control center reminds one less of an operations center for deep space travel than a high school computer lab. Blue Christmas lights strung across the wall are meant to simulate the glow of the spacecraft’s thrusting ion engines. In the hallway, a plastic trash can catches a steady drip of water that’s been leaking from the ceiling for months.
Rayman, who leads the team, is an animated, playful scientist with a deep love of deep space and cartoons on string theory and dark energy scotch-taped to his office door. At age 4, Rayman saw a meteor fly across the sky and announced, terrified, that it was a witch. But when his parents explained that the bright streak was actually something burning up in the Earth’s atmosphere, his terror was replaced with a fierce curiosity. By age 9, he was sending handwritten letters to the Russian Space Agency, requesting topographical maps of Jupiter’s moons.
Leading the Dawn mission is in many ways an extension of that childhood fascination. “I’ve had a lifelong love affair with the universe,” he said. “People throw around the word passion. It’s becoming a bit trite these days. But in my case, it’s an accurate description.”
A DAY ON DWARF PLANET CERES
At 6:45 a.m. on Jan 13, Rayman saw it: the first picture from the asteroid belt to reveal any detail of Ceres. He had hoped to see the bright features again, and the image contained just that, confirmation that they existed. It was a strong sign that the bright spots observed with Hubble were “real and persistent,” he said. The spacecraft would get closer and the images better over the coming months, he knew, but it was clear the team had some big questions to answer.
Ceres is the largest object in the asteroid belt, and contains one-third of all the mass there. It is 1.1 million square miles — the size of Texas, California and Alaska combined. Its gravity has made it round. And something, possibly carbon-rich compounds on its surface, makes it dark. Ceres has a reflectivity, or albedo, of 9 percent. For comparison, the moon, on average, reflects about 12 percent. Most asteroids reflect about 20 percent. And Vesta is a whopping 42 percent.
“It’s not like you’d be standing on black tar on Ceres,” Rayman said. “It’s dark, but not unimaginably dark.”
Throughout history, Ceres has waxed and waned in importance. After its discovery in 1801 by Giuseppe Piazzi, who named it after the Roman goddess of the harvest, it enjoyed a half century as a solar system VIP: a full-fledged planet. But not long after, it was downgraded to an asteroid. In 2006, it was again reclassified, this time as a dwarf planet. At the same time Pluto got demoted, Ceres got an upgrade.
Scientists know a good deal about Ceres already, considering its distance. They know that a Cerean day is nine hours. They believe it has a substantial amount of ice. And they think it’s a protoplanet, meaning it began to develop as a normal planet, until its formation was halted, likely blocked by the tremendous gravity of Jupiter. They also know its mass now, thanks to Dawn: 1.03 billion billion tons.
But so much about the dwarf planet is still unknown. The specifics of its composition. And of course, the source and nature of the bright spots. The mission of this mission is to change that.
When Dawn slipped into orbit around Ceres in March, it became the first spacecraft ever to orbit two extraterrestrial destinations. The plan calls for Dawn to circle Ceres at four different orbital positions — each at a different altitude. It is currently in its second orbit, flying at an altitude of 2,700 miles. And as Dawn drops closer to the surface, a richly-detailed view of the dwarf planet will emerge. Between now and the end of the year, Ceres will come increasingly into focus.
That’s already starting to happen. Take the bright spot. What in January looked like one spot expanded to two dots as Dawn got closer. The most recent images show many different spots — at least eight. And by the time it gets to its closest position, the picture will be 850 times sharper than the original 2003 Hubble photo, 12 times sharper than the pictures we’re seeing now.
“To me, the great surprise from Dawn’s observations was that the closer we got, the smaller that bright region became, and so the more reflective it had to be in order to have shown up earlier,” Rayman said.
Keri Bean, an engineer on the Dawn team, points out an image mounted on the wall in their mission control center. The shot is of Vesta, and it was captured by Hubble before Dawn arrived. Vesta looks like nothing in the image, a blob. “All we knew then was a tiny, fuzzy smudge in the sky,” she said. Then she points to another shot of Vesta, also hanging on the wall. This one is a composite, made from many smaller images taken by Dawn when the probe was at its lowest-altitude orbit. This image is almost 2,000 times sharper than the first, and the detail is extraordinary: it shows smooth and densely cratered regions, dark and lighter regions, giant mountains, and minerals on the surface.
JPL – Mission control at NASA’s Jet Propulsion Laboratory. Image by Justin Scuiletti
ABOUT THOSE BRIGHT SPOTS
On Ceres, there are many possible explanations for the bright spots. JPL scientists say they could be ice or salty remnants of evaporated ice. What they’re most definitely not, they say, are signs of an alien space station, as some UFO hunters claim. Members of the Dawn team expect they’ll have the question answered soon, possibly later this summer. But even then, many questions will remain. Where did the ice come from, for example? Was it excavated from an impact? Or is it coming from the interior of the planet?
Bonnie Buratti, a planetary astronomer with JPL who is not on the Dawn team, believes the images are showing water from the planet’s interior.
“I’m speculating, but there are two reasons,” she said. “It’s inside a crater. And it doesn’t look like an impact event. It looks like dots, vents, in an area of weakness.”
If she’s right, that means Ceres could have a liquid water mantle underneath its crust.
The bright spots are not the only evidence that Ceres harbors water. In 2014, scientists at the European Space Agency announced that the Herschel space telescope had discovered a thin veil of water vapor near Ceres. Unfortunately, Rayman said, this was more than six years after Dawn had launched, too late to install instruments to detect water vapor in space. (If there is water vapor, he said, there’s not a lot of it. “This spacecraft isn’t going to need windshield wipers.”)
But it could suggest that ice on the surface is changing from solid to gas.
And scientists suspect something else might be happening on the Ceres surface: cryovolcanoes, or ice volcanoes — those are the vents Buratti referred to. In other words, volcanoes that erupt ice instead of lava, not so unlike the geysers found on Tritan, a moon of Neptune.
“If there are cryovolcanoes, their energy has to come from somewhere,” Rayman said. “Something has to propel that water, has to heat it up and shoot it up from beneath, and so this would tell us something about the subsurface: the deep underground geology of Ceres. It would mean it’s not a static, dead, cold interior, but rather that there’s heat there driving some geological processes.”
Which leads to another natural question. Could there be life on Ceres?
It’s possible, Buratti said. “You look at Antarctica. There are lakes underneath the ice cap there. There have been probes sent down there, and it’s teeming with life. There’s bacterial life down there in these subsurface oceans that are like pockets of water a mile or two underneath the earth.”
Life, scientists believe, requires three things: water, food and a source of energy. On Ceres, there’s evidence of water, just as there is on Jupiter’s moon, Europa and Saturn’s moon, Enceladus. Organic compounds on the Ceres surface could provide food; radioactive nuclear decay from the planet’s interior is a possible source energy.
ARRIVAL – This artist’s concept shows NASA’s Dawn spacecraft arriving at the dwarf planet Ceres, the most massive body in the asteroid belt. The Dawn mission is the first to visit a dwarf planet — a round body that orbits the sun but, unlike a planet, does not clear its orbital path of other objects. Image by NASA/JPL-Caltech
If there was life, it would be primitive bacterial life, not walking, talking, thinking life. But still … life?
“If I had to bet money, I’d probably bet no,” Buratti continued. “But if I were to choose a place where there is life in the solar system, Ceres would be one of the places. Europa, Enceladus and Ceres.”
There are other interesting features. Ceres is spotted with craters, indentations caused by flying objects excavating surface material. The southern hemisphere is less densely cratered than the northern. There are mountains and ridges and smooth areas that look as if something flowed across them. Curved lines, or cracks across the surface may be signs of the dwarf planet distorting as it cools off, like stretch marks in the crust.
The brightest spots on dwarf planet Ceres are seen in this image taken by NASA’s Dawn spacecraft on June 6, 2015. Image by NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
On June 10, Rayman pulled up a crop of just-released images on his computer. It was the first time he’d seen these new photos.
“Okay, now this is cool,” he said. “Just look at how many different features there are.” He traced a curved line on the Ceres surface with his cursor. “There’s an indentation there, there’s an extension there.”
He moved his cursor to one of the bright spots inside one of the craters.
“Here’s a crater that’s 55 miles or so across, and both in the center and on the side, there’s something that’s bright,” Rayman said. “Is it active? Is it something coming up from the surface that’s reflecting light or is it something resting on the surface itself? And how did it get there? And for that matter, why is it there and not there … or there or there? There’s a lot here to wonder about.”
He looks up, and his tone becomes, for a moment, more contemplative.
“This is a mission of humankind,” Rayman said. “We’re exploring a distant alien world … for us. It’s not for Ceres sake, it’s not for Dawn’s sake. It’s something everyone participates in. And we all want to be transported far from home. We all want to know what it would look like if you were really there.”
Outside his window, the fog was lifting, the sage and live oak dotting the San Gabriel Mountains becoming more visible, changing the view entirely.
Video by Justin Scuiletti and graphics by Megan Hickey.
Jenny Marder is a senior science writer for NASA and a freelance journalist. Her stories have appeared in the New York Times, the Washington Post and National Geographic. She was formerly digital managing editor for the PBS NewsHour.
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