In September 2011 , the Herschel Space Observatory performed an observation campaign with the PACS photometer observing the asteroid ( 101955 ) 1999~RQ $ _36 $ in the far infrared . The Herschel observations were analysed , together with ESO VLT-VISIR and Spitzer-IRS data , by means of a thermophysical model in order to derive the physical properties of 1999 RQ _ { 36 } . We find the asteroid has an effective diameter in the range 480 to 511 m , a slightly elongated shape with a semi-major axis ratio of a/b=1.04 , a geometric albedo of 0.045 ^ { +0.015 } _ { -0.012 } , and a retrograde rotation with a spin vector between -70 and -90 ^ { \circ } ecliptic latitude . The thermal emission at wavelengths below 12 \mu m -originating in the hot sub-solar region- shows that there may be large variations in roughness on the surface along the equatorial zone of 1999 RQ _ { 36 } , but further measurements are required for final proof . We determine that the asteroid has a disk-averaged thermal inertia of \Gamma =650 Jm ^ { -2 } s ^ { -0.5 } K ^ { -1 } with a 3- \sigma confidence range of 350 to 950 Jm ^ { -2 } s ^ { -0.5 } K ^ { -1 } , equivalent to what is observed for 25143~Itokawa and suggestive that 1999~RQ $ _36 $ has a similar surface texture and may also be a rubble-pile in nature . The low albedo indicates that 1999~RQ $ _36 $ very likely contains primitive volatile-rich material , consistent with its spectral type , and that it is an ideal target for the OSIRIS-REx sample return mission .