Book where aliens come through a space gate in the solar system to attack Earth

Question

I'm looking to identify a book I read 10+ years ago about aliens who come through a space gate near Mars or Jupiter. They defeat Earth's space military and come to Earth to kill all humans. But they decide to blow up the planet. They see a spaceship that they missed go through the space gate that they came through.

Humans come out of the space gate and search for a planet to land on. They find one, but it has alien life on it. They land on the alien planet and meet the aliens living there. The aliens welcome them once they find out they are the last of their species. The humans and aliens become allies, and the book ends.

I remember that before Earth got blown up, the aliens were shooting at Earth, and the Atlantic Ocean rose high and destroyed a major city then they blow up Earth. I don't remember which city the Author was describing. Yet

Answer 1

While the details don’t quite match, I think that may be The Forge of God by Greg Bear. There’s a sequel, Anvil of Stars.

The novel features scenes and events, including the discovery of a nearly-dead alien in the desert, who clearly says in English, "I'm sorry, but there is bad news," and the alien's subsequent interrogation and autopsy; the discovery of an artificial geological formation and its subsequent nuclear destruction by a desperate military; and the Earth's eventual destruction by the mutual annihilation of a piece of neutronium and a piece of antineutronium dropped into Earth's core.

There is another alien faction at work, however, represented on Earth by small spider-like robots that recruit human agents through some form of mind control. They frantically collect all the human data, biological records, tissue samples, seeds, and DNA from the biosphere that they can and evacuate a handful of people from Earth. In outer space, this faction's machines combat and eventually destroy the attackers but not before Earth's fate is sealed. The evacuees eventually settle a newly terraformed Mars while some form the crew of a Ship of the Law to hunt down the home world of the killers, a quest described in the sequel, Anvil of Stars.