Hundreds of tons/tonnes per year hit our atmosphere, but most burn up before impact.
Mars has no atmosphere to speak of, and Venus has too thick an atmosphere. We need Jump drive, or something similar, to spread out to other solar systems.
One mention on 'How the Universe is Made' suggested the possibility that our Oort Cloud is close to, or might be part of, the Oort Cloud around Alpha Centauri A-B system. Astronomers on that show stated its possible our Oort Cloud goes out 2 light years and so does that system's Cloud. They said it might be posible to go from one Oort Cloud to another one, but it would be very slow. Thats about 26 trillion miles to travel.
