Dawn has arrived at Ceres
March 6, 2015
Chuck Bednar for redOrbit.com – @BednarChuck
After a journey of more than 7 1/2 years, NASA’s Dawn spacecraft was expected to enter orbit around Ceres, the largest object in the asteroid belt between Mars and Jupiter, this morning.
In a statement, the US space agency announced that Dawn was approximately 38,000 miles (61,000 kilometers) from Ceres when it was captured by the dwarf planet’s gravity at about 4:39 am PST (7:39 am EST) Friday morning. NASA personnel received a signal from the spacecraft confirming that it was healthy and operational at 5:36 am PST (8:36 a.m. EST).
“We feel exhilarated,” said Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles (UCLA). “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.”
Reconnaissance of an entirely new world
According to BBC News, Dawn was expected to enter orbit around the planetoid at about 7:20 am EST on Friday, barring any unexpected issues. For the next 14 months, the probe will study Ceres, dwarf planet in the inner solar system and the first to be visited by a spacecraft.
Dawn’s study of Ceres should provide new insight into the origins of the solar system, and since it has been travelling at a relatively slow speed, it was anticipated to have a smooth entry into the gravitational field of the dwarf planet. At closest approach, Dawn will be approximately 40,000 kilometers (under 25,000 miles) from Ceres, the British news outlet added.
“This is a first reconnaissance of an entirely new world,” Marc Rayman, Dawn’s chief engineer and mission director, told USA Today. UCLA’s Christopher Russell, principal investigator of the mission, added that Ceres has been like a “secretive neighbor” and that everything that he and his colleagues have witnessed so far during the mission has been “unexpected.”
Figuring out the bright spots
Among the surprises revealed by the planetoid thus far was a pair of bright spots discovered by Dawn during its approach. The spots, which thus far have been too small for an in-depth analysis yet remain brighter than anything else on Ceres, could be ice, salt or volcanic activity.
“As the spacecraft spirals into closer and closer orbits around the dwarf planet, researchers will be looking for signs that these strange features are changing,” NASA said earlier this week in a statement. Such changes “would suggest current geological activity,” the agency noted.
“Studying Ceres allows us to do historical research in space, opening a window into the earliest chapter in the history of our solar system,” added Jim Green, director of the Planetary Science Division at the NASA headquarters in Washington. “Data returned from Dawn could contribute significant breakthroughs in our understanding of how the solar system formed.”
The final countdown
Dawn began its final approach phase toward Ceres in December, and during its journey it has captured several optical navigation images and made two rotation characterizations, NASA said. This has made it possible for scientists to observe the object throughout the entire course of its nine-hour rotation, and it will continue to provide increasingly quality high-resolution photos of Ceres throughout the course of its mission, agency officials added.
“Scientists know that Ceres once had an icy ocean at its core and probably still does. But it’s also possible that radioactivity inside the planet melted some of the ice, creating a lake or a sea. Dawn will look for a liquid ocean,” USA Today said. If they find it, science team member Mark Sykes said, it could indicate that Ceres is or once was capable of supporting subsurface life.
Interrupted by Jupiter
Ceres, which was discovered by Sicilian astronomer Father Giuseppe Piazzi in 1801, is the second destination for Dawn, which had previously visited the giant asteroid Vesta in 2011 and 2012. While in orbit around Vesta, the spacecraft captured more than 30,000 images and several measurements of the object, revealing new information about its composition and geology.
With an average diameter of 590 miles (950 kilometers), Ceres is much larger than Vesta, which has an average diameter of just 326 miles (525 kilometers). Ceres, which contains approximately one-third of the entire asteroid belt’s mass, was initially classified as a planet and later called an asteroid before being re-designated a dwarf planet along with Pluto and Eris in 2006.
Carol Raymond, deputy principal investigator at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, explained that both Ceres and Vesta “were on their way to becoming planets, but their development was interrupted by the gravity of Jupiter. These two bodies are like fossils from the dawn of the solar system, and they shed light on its origins.”
“By studying Vesta and Ceres, we will gain a better understanding of the formation of our solar system, especially the terrestrial planets and most importantly the Earth,” she added. “These bodies are samples of the building blocks that have formed Venus, Earth and Mars. Vesta-like bodies are believed to have contributed heavily to the core of our planet, and Ceres-like bodies may have provided our water.”