By Paul Rincon
BBC News science reporter
Japan's space agency has lost contact with a robotic probe that it dispatched to explore the surface of an asteroid, according to reports.
Hayabusa captured its shadow on the surface of Itokawa
The small probe called Minerva was released from its mothership Hayabusa on Saturday, but officials say its "current status is still unknown".
Hayabusa is hovering near asteroid Itokawa, in preparation to collect surface samples for return to Earth.
It should begin its return voyage to Earth next month to arrive in 2007.
But the loss of Minerva comes as a blow to Japan's ambitious plan to make the first two-way trip to an asteroid.
"[Minerva] didn't touch down and we're not sure where it will go," Japanese space agency (Jaxa) spokesman Kiyotaka Yashiro said. "Hayabusa took a photo of Minerva floating between it and the asteroid. It was just a dot."
The 600g cylindrical probe Minerva was to have photographed the asteroid's surface and recorded temperatures there.
"Sending Minerva to the surface did not work," Junichiro Kawaguchi, the mission's project manager, told Japan's Asahi Shimbun newspaper.
"Hayabusa is jerking in an awkward manner, likely due to a malfunction of its positioning control system, but we want to fix that in time for its landing on 19 November."
Professor Alan Fitzsimmons of Queen's University, Belfast, UK, told the BBC News website: "The spacecraft was trying to maintain position at about 55m above the asteroid. Unfortunately, at the moment it released the robot it was firing its thrusters to move away and the robot did not move down to the surface of the asteroid."
Instead, it seems to have drifted into space. But there has been some good news for the mission. On Saturday, it successfully completed a practice approach to the asteroid.
A previous "dress rehearsal" had to be aborted on 4 November. The spacecraft was within a few hundred metres of the giant space rock when the operation was called off.
Jaxa said the descent was cancelled when it received an "anomalous signal" from the craft.
Hayabusa will now attempt its sample-collection landings on 19 and 25 November.
"Itokawa is fairly typical in size of the asteroids we detect on a day-to-day basis," said Professor Fitzsimmons.
"It was hoped it would scoop up samples from two regions of the asteroid and return them for study in laboratories on Earth. This has never been done before [for an asteroid]."
The spacecraft lost one of its three stabilising reaction wheels on 31 July, forcing it into an alternative flight mode. The second wheel failed on 3 October.
Mission managers said that they had altered flight parameters so that the craft still had enough fuel to make the landing attempts.
Hayabusa is due to begin its return voyage to Earth in December and is expected to arrive in June 2007.