The fact is your rooftop is covered with dust particles from meteorites. Outerspace is full of debris. Every day, thousands of meteorites invade our home but thanks to atmosphere for keeping us safe from them :D When these meteorites enter our atmosphere, they experience resistance to the particles present in our atmosphere. As a result they catch fire(and eventually melts) and lose all their energy before falling on the surface. This happens with very small sized meteorites but when bigger ones enter, they surely hit the surface because they are difficult to melt. Thanks to Jupiter for saving us from asteroids. Bigger ones rarely enters our atmosphere because of Jupiter's gravitational pull. It lures all the debris towards itself (:
