The cause of Spirit's silence may never be known

Spirit has been incommunicado for more than a year despite daily calls by NASA. The cause of Spirit's silence may never be known, but it's likely the bitter Martian winter damaged its electronics, preventing the six-wheel rover from waking up. The space agency tried every trick to listen for Spirit to no avail. Project manager John Callas of NASA's Jet Propulsion Laboratory said the last commands will be sent up Wednesday. Though orbiting spacecraft will continue to listen through the end of May, chances are slim that Spirit will respond.