Admissible height of local roughness of Titan's landscape

Titan's landscape has been formed by both short‐term phenomena, such as internal tectonic processes and atmospheric activity, and long‐term factors of planetary scale, such as global stress and gravity forces. Short‐term phenomena can be ignored since the timescale of any relaxation process 5 × 10 14 s is shorter than Titan's lifetime 1.4 × 10 17 s. Global stress can be ignored as well, because Titan's figure is practically a right sphere. Thus both Titan's body as a whole and the crust in particular are free from any stress, except the gravity force. For the cold, stable, incompressible Titan, the only significant relief‐forming factor is the counteraction between the gravity force and the crust's ability to resist this force. This results in a simple estimation of the maximal height of any admissible feature located above ocean level (RAOL) H max = 3σ/ρ g . The issue is the proper estimation of the crust density and real shear stress. Chemically, Titan's crust is an ice‐rock medium, while physically, it is a frozen two‐phase system, the density of the crust being equal to 1.81 × 10 3 kg m −3 . Titan's crust is considered here to be similar to Earth's permafrost, corrected for a lower temperature. This medium was treated as a quasi‐isotropic entity that is subjected to a slow viscoelastic deformation, the ultimate shear stress being equal to 2.15 MPa. The estimation of the admissible height of Titan's RAOL results eventually in H max ∼ 1900 m. The validity of the gravitational approach was verified by the calculation of known H max for the rocky inner planets, Earth, Venus, Mars, and the icy Jovian satellites, Ganymede and Callisto, and it appears to be reliable within ∼50%.