Board Thread:Warhammer 40k General Discussion/@comment-24383134-20140105071847/@comment-3258762-20140112102328

Yes, but Malcador didn't direct the Astronomican, he stopped the Warp from flooding into the materium through the hole in the webway. Terra is closer to daemonic infestation than even Cadia, but nothing happens because the Emperor holds them at bay. If he blinked out just a second they would swarm through like rats running from a fire (As was seen when Magnus tore open the Webway)