The Sunborn — Gregory Benford

Their historic mission to Mars made Julia and Viktor the most famous astronauts of all time. Now, decades later, they are ordered by the Consortium to Pluto, where they will rendezvous with another star- ship led by the brilliant, arrogant Captain Shanna Axelrod. Here, on the frozen ammonia shore of Pluto's methane sea, Shanna has discovered intelligent creatures thriving in the -300 degree temperatures. But even as their findings shift from the amazing to the inconceivable, the two crews must overcome their own intense rivalry to work together. For the most remote reaches of the solar system are filled with unimaginable wonders...and countless forces that will crush all human life.