The radio silence from NASA's Opportunity Rover has now lasted for four months. The robotic device, which is located on the rim of Mars' Endeavour Crater, has been silent since a dramatic dust storm encircled the red planet on June 10. Skies eventually cleared by mid-September, when America's space agency began a six-week listening programme to try and receive data from their device. However, that's already nearing expiration and the solar-powered robot remains dormant - possibly even dead. Opportunity fell silent back in June, with no way to power its solar battery as dust continued to block out the sun.