Question: What American science fiction author and astrophysicist, wrote the 1987 novel, Great Sky River?
Context: Joe William Haldeman (born June 9, 1943) is an American science fiction author.  He is best known for his 1974 novel "The Forever War".  That novel, and other of his works including "The Hemingway Hoax" (1991) and "Forever Peace" (1997), have won major science fiction awards including the Hugo Award and Nebula Award.  For his career writing science fiction and/or fantasy he is a SFWA Grand Master and since 2012 a member of the Science Fiction Hall of Fame. George Oliver Smith (April 9, 1911 – May 27, 1981) (also known by the pseudonym Wesley Long) was an American science fiction author.  He is not to be confused with George H. Smith, another American science fiction author. Asimov's Science Fiction (ISSN 1065-2698) is an American science fiction magazine which publishes science fiction and fantasy named after science fiction author Isaac Asimov.  It is currently published by Penny Publications.  From January 2017, the publication frequency is bimonthly (six issues per year). Robert Augustine Ward "Doc" Lowndes (September 4, 1916 – July 14, 1998) was an American science fiction author, editor and fan.  He was known best as the editor of "Future Science Fiction", "Science Fiction", and "Science Fiction Quarterly", among many other crime-fiction, western, sports-fiction, and other pulp and digest sized magazines for Columbia Publications.  Among the most famous writers he was first to publish at Columbia was mystery writer Edward D. Hoch, who in turn would contribute to Lowndes's fiction magazines as long as he was editing them.Lowndes was a principal member of the Futurians.  His first story, "The Outpost at Altark"for "Super Science" in 1940, was written in collaboration with fellow Futurian Donald A. Wollheim, uncredited. The Cosmic Puppets is a novel by American science fiction author Philip K. Dick, published in 1957.  It is a revision of "A Glass of Darkness", first published in the December 1956 issue of "Satellite Science Fiction".  In addition to using elements of science fiction, fantasy and horror, "The Cosmic Puppets" also functions as a "small town" novel in the popular sense. Great Sky River is a 1987 novel written by author Gregory Benford as a part of his Galactic Center Saga series of books. The Road to Science Fiction is a series of science fiction anthologies edited by American science fiction author, scholar and editor James Gunn.  Composed as a textbook set to teach the evolution of science fiction literature, the series is now available as mass market publications. Gregory Benford (born January 30, 1941) is an American science fiction author and astrophysicist who is on the faculty of the Department of Physics and Astronomy at the University of California, Irvine.  He is also a contributing editor of "Reason" magazine. John Boyd was the primary pen-name of Boyd Bradfield Upchurch (October 3, 1919 – June 8, 2013), an American science fiction author.  His best known work is his first science fiction novel, "The Last Starship from Earth", published in 1968.  Boyd wrote eleven science fiction novels, five other novels, and one biography.  The majority of his novels were published by US publisher Weybright & Talley, with later ones appearing from SF publishers.  He was born in Atlanta, Georgia. Gardner Raymond Dozois ( ) (born July 23, 1947) is an American science fiction author and editor.  He is the founding editor of "The Year's Best Science Fiction" anthologies (1984–present) and was editor of "Asimov's Science Fiction" magazine (1984–2004), garnering multiple Hugo and Locus Awards for those works almost every year.  He has also won the Nebula Award for Best Short Story twice.  He was inducted by the Science Fiction Hall of Fame on June 25, 2011.
Answer: Gregory Benford