  Extensive equatorial linear dunes exist on Titan, but the origin of the sand,
which appears to be organic, is unknown. We used nanoindentation to study the
mechanical properties of a few Titan sand candidates, several natural sands on
Earth, and common materials used in the Titan Wind Tunnel, to understand the
mobility of Titan sand. We measured the elastic modulus (E), hardness (H), and
fracture toughness (Kc) of these materials. Tholin's elastic modulus
(10.4+/-0.5 GPa) and hardness (0.53+/-0.03 GPa) are both an order of magnitude
smaller than silicate sand, and is also smaller than the mechanically weak
white gypsum sand. With a magnitude smaller fracture toughness
(Kc=0.036+/-0.007 MPa-m^(1/2)), tholin is also much more brittle than silicate
sand. This indicates that Titan sand should be derived close to the equatorial
regions where the current dunes are located, because tholin is too soft and
brittle to be transported for long distances.
