Perched on a rock, she could be waiting for a bus. But if so, she could be in for an awfully long wait. This photo of what looks remarkably like a female figure with her arm outstretched, was taken on Mars. Perhaps unsurprisingly, it has set the Internet abuzz with claims that there really is life on the red planet.

Others may well feel that it is simply an optical illusion caused by a landscape. The image was among many sent back to Earth by Spirit, Nasa's Mars explorer vehicle which landed there four years ago. Initial inspections revealed nothing unusual, but closer examination by amateur astronomers has thrown up this intriguing picture.

As one enthusiast put it on a website: "These pictures are amazing. I couldn't believe my eyes when I saw what appears to be a naked alien running around on Mars." Another, dismissing cynicism about the somewhat stony look of the "alien", wrote: "If you show me another rock in another photo from Mars, or Earth, that naturally looks like that, I will reconsider.

" A third contributor, who might have come closer to the majority view, said: "Ah, the human eye can be tricked so easily."

Whatever the people says but it seems real.