Scientists in bind over lost probe

This photo of comet 67P was taken from comet probe Philae's mother ship, space probe Rosetta, from 30km away. Photo / AP

Finding Philae would jeopardise mothership mission

Europe's lost comet probe, Philae, is posing major problems for space engineers who are striving to pinpoint the little craft after it disappeared from view during its troubled landing on the comet 67P in November.

Proposed manoeuvres to allow its mother ship, Rosetta, to uncover its exact location have caused alarm among some scientists, who fear changes in Rosetta's flight path could disrupt planned observations of the comet later this year. Comet 67P is set to make its closest approach to the sun in August and scientists want Rosetta perfectly placed to monitor the geysers of dust and water vapour that will pour from its surface.

"We never expected that we would lose Philae and would end up having to look for it," Rosetta mission manager Fred Jansen told the Observer. "However, finding its location is a real priority - and a real headache."

The exact location of Philae needs to be known to interpret data from its instruments - in particular, signals from its Consert radiowave device. These were emitted by Philae when it landed, passed through the comet and were picked up by Rosetta, then positioned on the opposite side of 67P.

"That data is essentially an x-ray of the comet, and that makes it very valuable," said Jansen. "It gives a clear idea of the nature of its structure. But we need to know exactly where Philae was sitting when it sent out those signals, so that we know how to interpret the information."

Rosetta reached comet 67P in August last year after a 10-year journey across the solar system and revealed a twin-lobed object filled with craters, hills and cliffs. Rosetta then released Philae on November 13. The little landing craft was supposed to employ thrusters and harpoons to attach itself to the comet's surface. But these failed and Philae bounced several times before eventually settling (at an angle of about 30 degrees) in rough terrain in the shadow of a cliff or crater wall.

Its radio continued to transmit data, which revealed that the comet had a surface of hard ice and was covered by a thick layer of dust in which organic chemicals could be detected. However, the lander could not use its solar panels to recharge its batteries because it was stuck in shadow.

On November 16 it ceased transmission and European Space Agency engineers have failed to pinpoint it.

"Basically we are not going to get a chance to find Philae until after August 14 when the comet will make its closest approach to the sun," said Jansen.

- Observer