Impact: Titan: Hard Science Fiction

How to avoid killing Earth if you don't even know who sent the killer250 years ago, humanity nearly destroyed itself in the Great War. Shortly before, a spaceship full of researchers and astronauts had found a new home on Saturn's moon, Titan, and survived by having their descendants genetically adapted to the hostile environment.The Titanians, as they call themselves, are proud of their cooperative and peaceful society, while unbeknownst to them, humanity is slowly recovering back on Earth. When a 20-mile-wide chunk of rock escapes the asteroid belt and appears to be on a collision course with Earth, the Titanians fear it must look as if they launched the deadly bombardment. Can they prevent the impact and thus avoid an otherwise inevitable war with the Earthlings?