Ceres appears as a crescent in this image captured by NASA's Dawn spacecraft on March 1 as it eased into orbit. The image was taken from around 30,000 miles (48,000 kilometers) away and will be the latest image available until mid-April. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
These two views of Ceres were acquired by NASA's Dawn spacecraft on February 12, 2015, from a distance of about 52,000 miles (83,000 kilometers) as the dwarf planet rotated. The images have been magnified from their original size. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
There was no dramatic entry. No high-risk maneuvers or nail-biting rocket firing. If NASA’s Dawn spacecraft missed on its slow crawl into orbit around the dwarf planet Ceres early Friday morning, engineers would have just tweaked the weak thrust of the ion engines and tried again.
Instead, mission managers say the real drama will be the science unveiled as NASA begins to chronicle the history of the largest unexplored body in the inner solar system. Astronomers already know that Ceres is an icy world, and because its core was once warm, it also would have had oceans in the distant past. What’s unclear is just how much water remains and if the dwarf planet was once habitable.
“Since its discovery in 1801, Ceres was known as a planet, then an asteroid, and later a dwarf planet,” said Dawn Chief Engineer Marc Rayman. “Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres home.”
Ceres — the largest member of the main asteroid belt — is actually Dawn’s second target. The spacecraft already spent 14 months exploring Vesta, the second-largest asteroid. Together, the pair account for 40 percent of the asteroid belt’s mass.
The rest of the belt represents a multi-billion-year record of collisions; however, astronomers believe these two icy bodies are protoplanets — the fossilized seeds of planets that might have been.
“Dawn is such a wonderful mission to explore that early part of the solar system because it’s right here in front of us today,” NASA’s Director of Planetary Science Jim Green said in a press conference Friday afternoon.
Sadly for space fans, the breathtaking photos will not come for more than a month. NASA’s latest image release, taken on March 1, shows Ceres as a crescent because Dawn is approaching from the world’s dark side and slowly maneuvering into a polar orbit that will allow it to image the entire surface. After that, the spacecraft will maneuver closer to map the mega-asteroid’s topography and then drop down even closer for a look at surface features as small as 130 feet (40 meters) across.
“We feel exhilarated,” said Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles. “We have much to do over the next year and a half, but we are now on station with ample reserves and a robust plan to obtain our science objectives.”
Among a number of objectives, astronomers hope to find out if the dwarf planet was once friendly to life. The limited images Dawn has already gathered of Ceres imply material moved from the interior onto the surface relatively recently. Vesta is covered in craters, but Ceres has large regions where the surface is smooth. And strange bright spots, seen only on Ceres, already have astronomers scratching their heads.
The European Space Agency’s Herschel spacecraft also found evidence of water near the dwarf planet last year, which has NASA on the lookout for any plumes streaming off the surface. Its density implies a mix of rock and ice, but the world’s exact makeup is another mystery Dawn hopes to explain.
“The bright spots and plumes are really symbols of what we’re after at Ceres,” said Carol Raymond, manager of NASA’s Small Bodies Program at the Jet Propulsion Laboratory in Pasadena, California. “We think there was an ocean on Ceres based on the heat that would have been coming out of the interior,” she added.
Raymond said that understanding Ceres’ watery past also has implications for our own planet. Such protoplanets would have rained in on the inner planets, bringing water along with incredible collisions. This same process is likely happening in other solar systems too. And because astronomers think dwarf planet Ceres is similar to its outer solar system cousin Pluto, what NASA finds in the next several months could be a preview of things to come from the New Horizons spacecraft this summer.
“We’ve got a lot to learn, and Ceres is that next step,” Green said.