Dawn came to Ceres on Friday morning, 6 March.
Early that day, NASA’s Dawn spacecraft, launched in 2007, entered into orbit around the dwarf planet Ceres for a 16-month investigation of the dwarf planet. Ceres is the most massive body in the asteroid belt between the orbits of Mars and Jupiter. That study could provide scientists with a much clearer picture of Ceres as well as a better understanding of the formation of terrestrial planets, according to the agency. Dawn is the first spacecraft to orbit around a dwarf planet.
“Ceres was discovered in 1801, and it has beckoned for more than two centuries. Finally today Dawn answered that cosmic invitation,” Marc Rayman, chief engineer and mission director for Dawn at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said at a 6 March news briefing. “At about 4:39 a.m. Pacific time today, Ceres reached out and tenderly took Dawn into its permanent gravitational embrace.” Orbit was achieved at an altitude of about 61,000 kilometers.
The Real Drama of the Mission
Rayman said that with the spacecraft’s advanced ion propulsion system, which is 10 times more efficient than conventional chemical propulsion, Dawn “gradually, elegantly, gracefully crept up on to Ceres and slipped into orbit.” He said the real drama of the mission “is in the opportunity to unveil the wonderful secrets of the largest unexplored world in the inner solar system.”
Carol Raymond, Dawn mission deputy principal investigator at the Jet Propulsion Laboratory, said that scientists think of Ceres and Vesta—an asteroid that Dawn explored in 2011 and 2012—as building blocks of the terrestrial planets. Ceres has an average diameter of about 950 kilometers, whereas Vesta has an average diameter of about 525 kilometers.
Raymond said those two bodies represent about 40% of the mass of the entire main asteroid belt. Moreover, they are very different objects than most of the other material there, which she said is largely collision debris “left over from the violent scattering of material by Jupiter’s gravity field” above the surface of Ceres.
“By the time we finish in mid 2016, we are going to know Ceres in exquisite detail, we are going to understand why it has very very bright spots which are unique to any body in the solar system that’s been explored thus far, and we are going to understand what Ceres means in terms of a building block for planets in our solar system,” Raymond said.
Understanding Other Rocky Planets
Jim Green, director of NASA’s Planetary Science Division, said that the exploration of Ceres will also help scientists better understand other bodies.
The area where Ceres and Vesta are located “is a region where a planet should have been, but no planet has been created. It’s a region where Jupiter’s gravitational interaction with this region has kept these pieces apart,” he said.
“Ceres, that protoplanet, that beginning seed of a planet, now allows us to look back in time to see how terrestrial planets are put together,” Green explained. “What we learn from Dawn about our building blocks, about this region, about these asteroids, I’m sure will also inform us about other solar systems and how rocky planets are created in those locations around stars,” Green said.
—Randy Showstack, Staff Writer
Citation: Showstack, R. (2015), Dawn spacecraft enters into orbit around dwarf planet Ceres, Eos, 96, doi:10.1029/2015EO026097. Published on 9 March 2015.