Curiosity is not NASA's only rover currently on Mars – the Opportunity rover has been on the red planet since 2004. But last year the rover has dropped out of communications when the planet and it has not been heard from since.
The Opportunity is solar-powered, and the storm kicked up so much dust that the sun's rays were blocked from reaching the planet's surface and recharging its batteries. The rover has not responded to contact from Earth over the past seven months has ignored over 600 calls, leading the NASA team to believe that it may no longer be able to continue its mission.
It was hoped that as the storm cleared, the wind would have blown away the dust which covered the rover's solar panels so the rover could recharge. But this has not happened, and the rover remains silent. NASA has been trying to contact the rover through a strategy called "sweep and beep," where they just say they are not responding, so they have not been so far. [1
"While we have not heard back from the rover and the probability that we are ever decreasing each day, John Callas, Project Manager for Opportunity at NASA's Jet Propulsion Lab, said in a statement.
These strategies are becoming urgent due to the six-month changeover to " Mars. The season of high winds which could be the source of opportunity's solar panels is coming to an end. NASA wants to try sending the new commands for several weeks, but if that does not happen, then it's likely the mission wants to be abandoned.