Galilée par son prestige a attiré nombre de visiteurs étrangers. Ils font le voyage pour le rencontre et discuter avec lui. À leur retour, ils propageront ses idées, pas nécessairement en tant que savants défenseurs des thèses galiléennes mais aussi en simples narrateurs.

In recent years and with the advent of dedicated observation programmes to discover new asteroids, as the Spaceguard Survey in USA, we have realised that the Earth orbit is regularly approached by thousands of small bodies ranging from kilometres to negligible sizes. Whereas the very small bodies do produce no substantial problems to life on Earth (maybe just some meteoroidal activity), the larger sizes (above tens of meters) can certainly imply effects ranging from local phenomena, as the ones experienced in Chelyabinsk in February 2013, to dramatic impacts affecting large areas and even provoking global damages (as in the case of the K-T extinction event). Solar dynamic models and observations of these bodies have permitted the derivation of Near Earth Object (NEO) population models and as a consequence the characterisation of the probability that the Earth encounters a minor body of a given size in a given time frame. Frequencies of once per century have been assessed for objects as the one occurred in Chelyabinsk (15-20 m). Such studies and the large number of bodies detected in recent years have prompted the question of how to avoid the danger posed by those with probabilities of impact, giving rise to a new discipline in the space sector which has been denominated Planetary Defense. International efforts are currently put in place to fully characterise the threat, design response actions to mitigate that threat and policies of international cooperation for such type of events whenever they can be foreseen. The seminar will address the presentation of the mitigation actions currently considered as well as the expected interaction with the theatening NEOs. A study case on the 2011 AG5 asteroid (now considered a no-threat case) will be presented.

Au milieu du 19e siècle, en géodésie, un basculement s'effectue de la domination française vers la domination allemande. La Belgique, royaume tout neuf, veut réaliser une carte de son territoire. Pour quelle méthode opter ? La française ou l'allemande ? Des savants vont enquêter. Je vous propose dans cette courte intervention de les suivre dans leurs investigations et de participer à leur choix.