The Ice-Fire Legacy

The mid twenty-first century brought many things to the population of earth. A mammoth space city called Alpha space station orbited a thousand miles above the world. Mars colony had a population of several thousand and a small, scientific community existed on earth's moon. Life was good and no one expected that change was coming . . . It would effect everybody.
A comet sixty miles in diameter was on a collision course for earth and it would arrive in five months.
Whatever happened to the earth would have no effect on the Mars colony that prepared to accept hundreds of refugees.