An image of a mysterious shape on the surface of Mars, taken by Nasa spacecraft Spirit, has reignited the debate about life on the Red Planet.A magnified version of the picture, posted on the internet, appears to some to show what resembles a human form among a crop of rocks.When the robotic rover set down on 24 January 2004, its images disappointed space-watchers hoping for signs of extraterrestrial life. Now they appear convinced that this image provides the evidence they have been trawling Nasa's photo files for. The blown-up image seems to resemble a figure striding among the Martian   read more »