The title page of Kepler's Dissertatio Cum Nuncio Sidereo

Astronomy recently celebrated the 400th anniversary of Galileo’s first observations with a telescope.  His discoveries, including four moons of Jupiter, were published in a sensational treatise, Sidereus Nuncius (The Sidereal Messenger), in 1610.

German astronomer Johannes Kepler received a copy of the Sidereal Messenger in early April that year.  His response, the ‘Conversation with the Sidereal Messenger’, was completed and sent to Galileo on 19th – 400 years ago next month. A slightly revised version was published on May 3.

In it, Kepler made the first observation of extraterrestrial artificial structures – circular fortresses on the moon!  Galileo had remarked upon these features, but it was left to Kepler to argue that because of their geometrical perfection, they must be artificial.

He elaborated his reasoning in his posthumously published Somnium (The Dream), arguing that ‘when things are in order, if the cause of the orderliness cannot be deduced from the movement of the elements or from the composition of matter, it is quite probably a cause possessing a mind’.

Kepler was in a sense applying the principle of mediocrity, upholding the Galilean notion that the Moon is a body comparable to the Earth in composition and in the forces acting upon it and not an orb of Aristotelian perfection or otherwise possessing features that made it a different order of object entirely.

Sketches of the Moon from Galileo's Sidereus Nuncius

Sketches of the Moon from Galileo's Sidereus Nuncius

Obviously Kepler was describing craters, which we now know to be naturally caused. Despite its disproof, his study of the lunar craters is historically significant as the first empirical study of purported extraterrestrial structures, which is close enough to archaeological for its time that I’ll claim it as the beginning of space archaeology.

I think a case could be mounted that it was the beginning of SETI, a turning point when the question of intelligent extraterrestrial life went from being theological or philosophical to being empirical and scientific.

He went on to speculate on the method of construction used by the lunar architects:

They drive a stake down in the center of the space to be fortified. To this stake they tie ropes which are either long or short depending on the size of the future town … With this rope fastened in this way, they move out to the future rampart’s circumference, as defined by the ends of the ropes. Then the entire population assembles to do the digging …

As literally the first person to consider this question, Kepler can be forgiven for assuming artificial origins – even Occam’s razor is arguably on his side if you consider that the lunar craters were unlike anything known on Earth, and that a meteoric explanation was unavailable to him.

Unfortunately, some people have not taken the lesson of Kepler and the craters to heart, and too quickly infer agency – not only for astronomical oddities like the Face on Mars, Kepler’s mistake has been noted and breezily dismissed as no longer possible by William Dembski, a proponent of intelligent design.

It is fitting that in the year of the 400th anniversary of space archaeology, that The British Interplanetary Society and The Institute for Archaeology, Birmingham University will be hosting the Archaeology for Space conference in September.