FEATURES OF THE INTERNAL STRUCTURE OF NEPTUNE'S SATELLITE TRITON.

Abstract

Neptune's moon Triton occupies a unique place among the bodies of the Solar System. It is a gravitationally captured object from the Kuiper Belt. During a close gravitational maneuver near Neptune, the planet's tidal forces tore Triton from its companion. Initially, Triton was in a very elongated orbit. Experiencing extreme tidal deformations during each pericentric passage, the amount of viscoelastic dissipation of Triton's tidal energy was converted from the mechanical energy of orbital motion into internal heat at a high rate. This led to the complete melting of ices and global melting of silicates in the interior of the newly arrived satellite, initiating a complete gravitational differentiation of matter into a silicate-metal core, a silicate mantle, a water ocean, and an ice shell. To maintain the ocean in a liquid state under conditions of low modern tidal heating, the presence of chemicals that lower the freezing point of water is necessary. Ammonia plays a leading role, the concentration of which in the Triton ocean can reach 10–15% by mass. The mixture of water and ammonia has a eutectic melting point at a temperature of ~ 176 K. In addition, contact with the mantle provides high salinity of the water, which makes the Triton ocean highly co nductive. Triton's outer crust consists mainly of water ice with admixtures of solid nitrogen, methane, carbon dioxide and carbon monoxide ices in the near-surface layer. The thickness of the crust is estimated from 60 to 150 km. Triton's surface is one of the youngest in the Solar System: its average geological age is estimated in the range from 10 to 100 million years, which indicates the renewal of the relief by cryomagmatic and tectonic processes. From an astrobiological point of view, Triton is one of the most promising objects in the Solar System for the search for extraterrestrial life. Gravitational parameters and low estimated dimensionless moment of inertia (C/MR 2  0.31) indicate a high central mass concentration and deep gravitational differentiation of the satellite's matter. Seasonal redistribution of volatile nitrogen ices can cause periodic wandering of the rotation poles, which imposes additional stresses on the lithosphere. The liquid state of the ocean at temperatures T ~ 176 – 230 K is maintained due to the high ammonia content (10 – 15%), which acts as an antifreeze, and heat dissipation from tilt tides.