We have performed high-precision astrometry of H _ { 2 } O maser sources in Galactic star forming region Sharpless 269 ( S269 ) with VERA .
We have successfully detected a trigonometric parallax of 189 \pm 8 \mu as , corresponding to the source distance of 5.28 ^ { +0.24 } _ { -0.22 } kpc .
This is the smallest parallax ever measured , and the first one detected beyond 5 kpc .
The source distance as well as proper motions are used to constrain the outer rotation curve of the Galaxy , demonstrating that the difference of rotation velocities at the Sun and at S269 ( which is 13.1 kpc away from the Galaxy ’ s center ) is less than 3 % .
This gives the strongest constraint on the flatness of the outer rotation curve and provides a direct confirmation on the existence of large amount of dark matter in the Galaxy ’ s outer disk .