An anomaly of an unknown nature has cut off data transfer from the Spirit rover on Mars for more than 24 hours, mission managers said Thursday. The news came a day after NASA said the rover was out of contact because of bad weather at a radar transmission site in Australia. On Thursday, project manager Peter Theisinger told reporters at NASA’s Jet Propulsion Laboratory that the loss of data did not appear to be due to the weather, but due to a “very serious anomaly on the vehicle.”