The probe, called Grail-A, went into lunar orbit after launching from earth in September and making a 3.5-month flight.
The small probe is due to be joined in moon orbit by its twin, Grail-B, later on January 1.
Scientists working with the U.S. space agency NASA say they hope the probes will help them gain insight into how the moon was formed.
The two probes are scheduled to fly above the moon’s surface to map its gravitational fields.
Scientists say the mission should provide more information about the mountainous far side of the moon that doesn’t face earth, and also test a hypothesis that earth once had two moons that collided and formed one.
compiled from agency reports