Eight Keys to Eden

Originally published in 1960, here is an enthralling science alien planet puzzle from Hugo Award winning writer Mark Clifton.
When Eden, the Earth colony eleven light years away, goes silent and fails to answer any communications from the mother planet, Earth's government goes into a panic. Has something tragic happened on a world already proven to have no intelligent, dangerous lifeforms? Or, are the colonists purposely disregarding the messages for some reason of their own? What could be...