Claims for evidence of extraterrestrial monuments can be divided into three main groups, based on location. First to be considered is the moon, Earth’s nearest neighbour and the focus of the earliest attempts at detailed survey by remote sensing. It is the only place other than earth that humans have so far visited (at least, according to conventional wisdom). Second is Mars, which has long been a favoured candidate for being the home of other forms of life. Thirdly are the other planets and their satellites. As human space probes reach further into the solar system (of the major planets, only Pluto—which many not be a true planet, after all—has not so far been visited, although there plans for a ‘Pluto Express’, to reach the planet in 2013), so we are learning more about other planets and their moons. It is interesting that Venus, which is supposedly better surveyed even than Earth, has not been the subject of speculation about alien life or monuments in recent years (apart from photographs in Childress’s Alien Archaeology that are captioned to suggest that there may be artificial structures on its surface): even the most enthusiastic believer in extraterrestrials recognises that it is too hostile a place to support any life whatsoever.