The Hayabusa space probe has moved to within 20 km of an asteroid orbiting the sun between Earth and Mars after a 24-month journey on a mission to bring rock samples and other data back to Earth, according to Japan's space agency.

The probe, launched in May 2003, was in a stationary orbit 20 km from the asteroid Itokawa as of Monday, the closest a Japanese probe has ever come to any space object, the Japan Aerospace Exploration Agency said. The asteroid is about 320 million km from Earth.

JAXA expects the mission to answer questions about the birth of the solar system.

A photo of the asteroid taken by Hayabusa shows some of its surface to be rocky while other parts are flat and smooth.

The probe will remain at a distance of 20 km for about a month to collect data on the asteroid using X-ray and infrared technology, and will then approach to within 10 km for further study.

In early November, the probe will briefly land on the potato-shaped asteroid -- 548 meters long, 312 meters wide and 276 meters high -- to take rock samples. It will repeat the feat one week later. Upon completion of its mission, the probe will head back to Earth, returning in June 2007.