The space probe Dawn has begun orbiting the dwarf planet Ceres on a voyage of discovery into the solar system's main asteroid belt, NASA says.
The probe - the first to orbit a dwarf planet - will stay over the mysterious body for sixteen 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 (2339 AEDT) on Friday some 61,000km 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 4.9 billion kilometres and 7.5 years, Dawn calls Ceres, home," said Dawn chief engineer Marc Rayman, who is also mission director at JPL.
Ceres is the largest known object in the asteroid belt between the orbits of Mars and Jupiter.
The dwarf planet, which has an average diameter of 950km, makes a full rotation every nine hours, and NASA is hoping for a wealth of data once the spacecraft's orbit begins.
