Deep beneath the Indian Ocean, that pull weakens to an extreme low, leaving what is considered a massive gravity ‘hole’ some three million square kilometers in size roughly where the seafloor sinks into a vast depression.One of the most profound gravitational anomalies on Earth, its presence has been alluded to for a while. Ship-based surveys and satellite measurements revealed long ago that the sea level just off the tip of the Indian subcontinent dipped on account of the gravitational tug-of-war between the aptly named Indian Ocean geoid low and the surrounding gravitational ‘highs’.Just what caused this relative weakening has never been clear. Now two researchers from the Indian Institute of Science think they have a better idea of the kinds of planetary phenomena that could be involved.