Ray Cummings 
A Brand New World 

The new planet came out of the infinite deeps of interstellar space, moved in towards the sun like a comet, and stayed — a new member of the Solar System, between Earth and Venus. Xenephrene it was named, and it made a pretty vision in the evening sky…until other things began to appear in the heavens. Flying things, strange visitants, mysterious lights — and people knew then that they were no longer alone. Xenephrene was inhabited, and its inhabitants were discovering the Earth. But were they coming as friends or as invaders? For trade or for conquest?