The Sails of Tau Ceti by Michael McCollum
Approx. 94,290 words.
Published on April 7, 2010.
Scientists are surprised to discover an alien light sail on the edge of the solar system. When the expedition sent to meet them boards the craft, they find beings surprisingly compatible with humans. That two species so similar could have evolved twelve light years from one another seems coincidental. One human soon discovers that coincidence has nothing to do with it.