The Martian Sphinx Author:Keith Woodcott By the twenty-firest century the world was drowning in its own population. A solution had to be found quickly- and it was, in "gravipower". Wonderful, unending source of power- only the scientists knew that its use was reducing the Earth's distance from the sun at a dangerous rate. But if another planet's gravipower could be harnessed... — An ... more »expedition was launched to Mars, known to be uninhabited- except that a woman was wandering around its surface who claimed she had come from another galaxy to warn Earth of a terrible menace, and there was a huge poly-hedron of metal emanating a force very much like that of gravipower.
Someone else had discovered it! A thousand years ago, or now? Friend, or enemy?