This light appear to be emerging out of the Martian surface. One blogger, Scott Waring, says "This could indicate there there is intelligent life below the ground and uses light as we do." A stretch, but not impossible. Another blogger, Phil Plait of BadAstronomy.com says, "a subatomic particle smacked into the camera, leaving behind its trail of energy." As the image appears on more than one frame of film, this is impossible. A more likely explanation is that the light is a piezoelectric effect much like ghost lights on Earth, such as the Marfa Lights.
UPDATE: Out There was reliably informed that there exists more than one image of this light, but it turns out that only one image has been released. We continue to believe that more than one image exists.