Other worlds

The moon and Mars have been the focus of most of the speculation about alien monuments and other traces of their activity. This is partly because they are very close neighbours and partly because they are much less hostile than worlds such as Venus (with its surface temperature that would melt lead and sulphuric acid rain) or Jupiter (a giant ball of volatile gases, so massive that its core is composed of metallic hydrogen). Mars, especially, was clearly once more earth-like than it now is. However, these problems with more distant worlds have not prevented some authors from detecting all manner of artificial structures on them.

Perhaps the most bizarre of the claims concerns the various planetary satellites or moons, especially of the outer planets. Several of them (the Saturnian satellites Mimas, Rhea and Tethys are the most obvious) have one exceptionally large crater with a central peak. Our own moon has a similar feature, the Mare Orientale on the very eastern edge of the side that faces earth. David Childress has suggested that these features are similar to the umbilical scars resulting from the blowing of glass spheres. The implication is that these satellites are hollow and artificial, claims once made for the Martian moons Phobos and Deimos. These are not hypotheses that archaeologists are equipped to evaluate. The opinions of astro-geologists, who are qualified to assess these objects and make deductions about their origins, are that planetary satellites are of much the same age as the planets they orbit and that they display all the characteristics of the same sorts of formation processes as the planets. Large craters of this type are most economically explained as the result of ancient impacts.