The US space probe Dawn began orbiting the dwarf planet Ceres Friday on a voyage of discovery into the solar system's main asteroid belt, NASA said Friday.
The probe -- the first to orbit a dwarf planet -- will stay over the mysterious body for 16 months to study its structure and gather clues to help mankind better understand how the planets were created.
The space probe was captured by the dwarf planet's gravity at 1239 GMT, some 38,000 miles (61,000 kilometers) from Ceres's surface.
About an hour later, it sent a signal to mission controllers at NASA's Jet Propulsion Laboratory in Pasadena, California to say it was "healthy and thrusting with its ion engine," the space agency said in a statement.
When it was discovered in 1801, Ceres was classified as a planet, only to be reclassified later as an asteroid and then a dwarf planet.
"Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres home," said Dawn chief engineer Marc Rayman, who is also mission director at JPL.
The dwarf planet, which has an average diameter of 590 miles, was first spotted by Sicilian astronomer Father Giuseppe Piazzi.
It makes a full rotation every nine hours, and NASA is hoping for a wealth of data to begin pouring in as the spacecraft orbits Ceres.
"We feel exhilarated," said Dawn principal investigator Chris Russell from 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."
- Two bright spots -
Around April or May, the probe will start to move in closer to make a first full assessment of the planet, and by November will be as near as 230 miles from Ceres's surface.
Scientists will be looking for signs of geologic activity via changes in two bright spots on the planet, or other features on Ceres' surface over time.
The mission will also help to better understand the origins of the solar system and the possibility of life (in the form of micro-organisms) on Ceres.
"Studying Ceres allows us to do historical research in space, opening a window into the earliest chapter in the history of our solar system," said Jim Green, director of NASA’s Planetary Science Division.
"Data returned from Dawn could contribute significant breakthroughs in our understanding of how the solar system formed."
The last images of Ceres were taken in March, and show a slim silver crescent, with most of the dwarf planet shrouded in darkness. But NASA scientists hope to capture sharper images during the mission once Dawn emerges from the planet's dark side.
Though this is the first mission to orbit a dwarf planet, Dawn explored the giant Vesta asteroid in 2011 and 2012. It gathered information and thousands of images before it set off for the years-long journey to Ceres.
Ceres and Vesta are the two largest bodies in the asteroid belt between Mars and Jupiter.
Launched in 2007, the $473 million Dawn mission is equipped with a high definition camera and two spectrometers. It is outfitted with an ion propulsion engine that allows it to reach high speeds and also make a slow approach to drop into orbit.
The US space agency has also set its sights on Pluto, and in 2006 launched the New Horizons spacecraft to study the dwarf planet.
Next year, the US space agency plans to launch its Origins-Spectral Interpretation-Resource Identification-Security-Regolith Explorer (OSIRIS-REx) spacecraft, to "study a large asteroid in unprecedented detail and return samples to Earth," NASA has said.