The U.S. space agency NASA is having trouble communicating with its robotic rover on Mars. Something has caused it to stop sending research data back to Earth.
Mission controllers at the Jet Propulsion Laboratory in California have heard only simple tones from the Spirit rover since early Wednesday. The tones are confirmations that it has received signals from mission controllers asking it to respond.
But Mission official Peter Theisinger says that the vehicle is not transmitting expected scientific or engineering data. "We now know that we have had a very serious anomaly on the vehicle, and our ability to determine exactly what has happened has been limited by our inability to receive telemetry from the vehicle."
Mr. Theisinger says technicians do not know the cause of the rover's problem and are struggling to diagnose it. "There is no one, single fault that explains all the observables that we know of at the present time that we can conceive," he said.
Spirit arrived at Mars nearly three weeks ago to search for signs of ancient water that would indicate the planet was once suitable for life. When the six-wheeled robot developed its communication problem Wednesday, it was preparing to drill into its first rock to look for chemical signatures of water.
The director of the Jet Propulsion Laboratory, Charles Elachi, says the rover's behavior is a sign it has put itself into a so-called "safe" mode after something went wrong aboard the spacecraft.
"[It] could be that for some reason there is some corruption in the memory of the spacecraft," he said. "It's similar to what happens at your computer at home. You know, sometimes some error comes in or some bugs come in. There could have been some rays that hit the spacecraft and disturbed some part of the memory. So it's behaving abnormally and the way we set the spacecraft is that if there is something abnormal, it goes into a certain safe mode."
The NASA official says that later Friday, mission engineers will attempt to command Spirit to run a diagnostic program and return data that will let them analyze and correct the trouble.
Similar troubles have occurred on previous U.S. Mars missions, including the Viking landers of the 1970s and Sojourner rover in 1997, but Mr. Elachi recalls that engineers solved the problem after careful analysis. He says there is no need to rush in this case either, as mission controllers face Sunday's arrival of a second, identical rover named Opportunity on the other side of Mars.
"There is no reason to rush to do action on Spirit. We know we have power. The fact that we got the signal back means lots of things are working right. So one of the decisions we will be making over the next 24 hours is how much time we spend on Spirit, and do we need to rush or do we keep it in quiescent mode and focus on Opportunity," he said.
NASA says Opportunity is on a perfect path to Mars, so ground controllers skipped a course correction maneuver planned for Thursday.