Japan's lunar explorer has successfully entered orbit around the Moon, space agency officials have said.
The orbit was launched by a Japanese H-2A rocket last month
The Kaguya orbiter was launched last month from Japan's space base on the southern island of Tanegashima.
It will deploy two smaller satellites and, over a year, gather data on the Moon's origin and evolution.
Japanese scientists say it is the most complex lunar mission since Nasa's Apollo programme in the 1960s and 70s, when astronauts walked on the Moon.
"We believe this is a big step," said Yoshisada Takizawa, a project manager at Japan's Aerospace Exploration Agency (Jaxa).
"Everything is going well and we are confident."
The three-tonne probe is formally called Selene, the Selenological and Engineering Explorer.
Its nickname, Kaguya, refers to a princess in a folk story who ascended to the Moon.
The main orbiting unit will ultimately be positioned 100km (60 miles) above the surface of the Moon, while two smaller satellites will be deployed in polar orbits. They will collect data on the Moon's geology, topography and environment, Japan's space agency said.
Engineers confirmed that the main unit had entered lunar orbit early on Friday, Mr Takizawa said. It will gradually move into a lower orbit as it maps the Moon's surface.
The data collection phase of the mission will begin in mid-December, he said.
Japan launched its first satellite in 1970, but in recent years its space programme has been hit by technical and financial problems.
It trails China, which in 2003 became the first Asian country to put an astronaut in space. Both China and India are expected to launch lunar probes in the next few months.
So Jaxa has been working to expand its activities - its stated aim is to achieve manned space flight by 2020.