Massive Martian dust storm threatens plucky NASA rover

By Will DunhamWASHINGTON (Reuters) - An immense dust storm that may soon encircle Mars is threatening one of NASA's rovers on the planet's surface, with the vehicle becoming dormant and unresponsive at a site called Perseverance Valley, U.S. space agency officials said on Wednesday.The officials, however, expressed optimism that the Opportunity rover, which was built to operate for three months but has thrived on Mars since January 2004, will be able to survive and continue its scientific missio