Sooner or later for good or ill, a united mankind, equipped with science and power, will probably turn its attention to the other planets, not only for economic exploitation, but also as possible homes for man. . . . The goal for the solar system would seem to be that it should become an interplanetary community of very diverse worlds . . . . Through the pooling of this wealth of experience, through this 'commonwealth of worlds,' new levels of mental and spiritual development should become possible, levels at present quite inconceivable to man.