In the Dialogo Galileo introduces an idea concerning the genesis of the planetary system, crediting Plato with its authorship. According to this idea, the "divine Architect" created the Sun and, in a certain distance from it, the planets. The planets, according to their "assigned tendencies", then began to fall towards the Sun in naturally accelerated motion. Upon reaching their predestined orbits, their linear motions were diverted into circular motions by the "divine Mind" thereby retaining their acquired velocities. Galileo's spokesman Salviati raises the question, whether all planets could have been created in the same place in order to account for the observed orbital velocities of the planets. He informs us that he has carried out the required computations and that they agree "truly wonderfully" with the observations. When the topic is brought up again six years later in the Discorsi, Salviati once more emphasizes that he had done the computation and "found it to correspond very closely to the observations".

These two passages in Galileo's major works provoked great interest among his contemporaries as well as among historians of science. Intrigued by the obvious falsity of Galileo's claim, as was first noticed by Marin Mersenne in 1637, historians have tried to understand the motives for Galileo's insistence on his cosmogony. Interpretative attempts focused on reconstructing computations possibly made by Galileo that would justify his claim.

A new interpretation of the content of six folios of Galileo's notes on motion (Codex Ms. Gal. 72) will be presented which, as is well known, contain these computations. The interpretation will be embedded in the wider context of the development of Galileo's theory of motion as it is documented in Ms. Gal. 72. Clues from such an interpretation allow us to date Galileo's first attempt at a cosmogony at a very early stage of the work on his new science of motion, that is at a time when he still adhered to the wrong principle of fall. The fact that Galileo started such an ambitious program when his theory of motion was yet so little developed is in accordance with the underlying thesis that the omnipresence of Aristotelian natural philosophy of the time almost unavoidably led engineer-scientists like Galileo to encounters with astronomical issues related to it. Furthermore, embedding a new science of motion within this dominating world view created boundary conditions that no attempt at a new science of motion could ignore. In particular, the fact that in Aristotelian natural philosophy terrestrial physics was an integral part of a global world view enforced a cosmological meaning on every mechanical model of astronomical phenomena. The interpretation will show how Galileo tried to cope with the situation by using projectile motion as a mental model of the divine creation of the planetary system and by scaling up his experiments with free falling bodies deflected into the horizontal to cosmic dimensions.