On some of those worlds, life is doubtless intelligent. Some of the intelligent ones have gone out into space. Once in space, these races look for signs of life on other worlds.
Chance alone dictates who meets what among the alien races in space.
As a rule, such meetings are the random result of explorers and trade ships, and not all such meetings have happy endings. Six hours ago, a ship of one of those races entered our solar system. A large, donut-shaped craft was spotted passing the rings of Saturn. In the first hour we learned the donut-shaped craft was enormous, easily big enough to nest the Earth in the hole at its center with plenty of room to spare. It moved above the plane of the system and centered that donut hole on the Earth.