The high albedo indicates that the surface of Tethys is composed of almost pure water ice with only a small amount of darker materials. The visible spectrum of Tethys is flat and featureless, whereas in the near-infrared strong water ice absorption bands at 1.25, 1.5, 2.0 and 3.0 μm wavelengths are visible. No compound other than crystalline water ice has been unambiguously identified on Tethys. (Possible constituents include organics, ammonia and carbon dioxide.) The dark material in the ice has the same spectral properties as seen on the surfaces of the dark Saturnian moons—Iapetus and Hyperion. The most probable candidate is nanophase iron or hematite. Measurements of the thermal emission as well as radar observations by the Cassini spacecraft show that the icy regolith on the surface of Tethys is structurally complex and has a large porosity exceeding 95%.