From October 1st, 2013 to December 31st, 2013, The Jim Henson Company and Grosset & Dunlap will accept writing submissions to find the author for a new novel set in the Dark Crystal world. The search is open to both published and unpublished writers.
At this point, they are looking for 7,500-10,000 words. This can be an inspirational short or actual chapters that would let them know what you plan to do with the full novel. The novel itself will ultimately be something over 50,000 words long.
For details on the time and culture of this prequel check out this page on the Dark Crystal web site.