Themsa is the second and smaller of Helevos's two moons, the larger being Thea. Themsa is a small, silvery, potato-shaped body that spins through the sky on it's long axis, so that one rotation is the basis of an hour in the Hirèrk Moonscale.
Themsa was almost certainly a large, elipsoid asteroid that narrowly avoided striking the surface, and instead was captured in orbit. Themsa is roughly potato-shaped with a large crater visible at one end, the result of an impact that set the moon spinning on it's vertical axis. The moon is often portrayed as a woman seen from the side, the narrower end being the head, the lower the body, and a ridge on one side being the arm and shoulder.