I nominate Neptune Crossing,
"When survey pilot John Bandicut falls into a cavern on Triton, his life changes forever... For the alien quarx, one hundred million years of solitude suddenly, comes to an end.
The quarx, of an eons-old interstellar civilization, uses advanced chaos theory to predict events, cannot by itself prevent the comet colliding with Earth. John Bandicut must help this disembodied alien, knowing that humanity's existence rides on the result. He has to break the rules and sacrifice everything, all he has ever known or loved to prevent a cataclysm that no human can possibly detect.
In a stolen ship, Bandicut can only hope to save the Earth. Even if he doesn't live to see it again..."