The Dawn spacecraft has entered orbit around Ceres, becoming the first man-made vehicle to circle a dwarf planet. The observatory, launched in 2007, was captured by gravitation from the body at around 7:39 a.m. EST on March 6. About 57 minutes later, the spacecraft signaled controllers that the vehicle had successfully entered orbit, and its ion engine was operating normally.
Ceres is the largest body within the asteroid belt, orbiting the Sun, between Mars and Jupiter. The second-largest member of that grouping is the asteroid Vesta. That object was also visited by the Dawn spacecraft, which observed Vesta from 2011 to 2012. With its arrival at Ceres, the observatory becomes the first vehicle from Earth to ever orbit two objects in the Solar System.
"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet. Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home," Marc Rayman, Dawn chief engineer and mission director at Jet Propulsion Laboratory (JPL), said.
Dawn approached the dwarf planet from the dark side of the body, so the first images show the object as a crescent. As the vehicle continues to approach the body, additional surface details will become visible, as more of the lighted side of the object is revealed. Mission engineers want to know how Vesta was formed, and if surface features are changing over time, which would suggest current geological activity on the dwarf planet.
"Studying Ceres allows us to do historical research in space, opening a window into the earliest chapter in the history of our solar system. Data returned from Dawn could contribute significant breakthroughs in our understanding of how the solar system formed," Jim Green of Jet Propulsion Laboratory said.
Ceres was discovered by Italian astronomer Giuseppe Piazzi in January 1801. At first, the body was believed to be a newly-discovered planet. However, as more objects were found in similar orbits, the object was classified as an asteroid. In 2006, Ceres was reclassified as a dwarf planet, along with Pluto.
Dawn is propelled by ion engines, which are much more efficient than chemical-based thrusters. This propulsion is what made it possible to reach a pair of orbits on the mission.
The vehicle is designed to spend around 16 months orbiting Ceres, examining its surface features and composition.
This mission will not be the only one to visit a dwarf planet this year. On July 14, the New Horizons spacecraft will arrive at Pluto, where it will explore that body, and at least five satellites.
