Despite its 10,000-million-mile diameter, the solar system  is  dwarfed by the 
Milky Way galaxy to which it belongs. But the Milky Way, containing 100,000 million 
stars, is only a mote in the universe. 
There are thousands of millions of such galaxies, most with their own myriad stars 
having their own planetary systems. If only 1/10,000 of 1 per cent of these planets 
harbour a civilization - and this is a very conservative estimate - the universe must teem with more than 100 million million civilizations.