Mapping of Monad Regio, Triton Reveals a Moon with Complex Geological History

A global color mosaic of Triton taken by Voyager 2 during its 1989 flyby. Monad Regio, the area of interest for this study, is right of center and along the terminator. Credit: NASA/JPL/USGS.

Triton, the largest moon of Neptune, is hypothesized to be a captured Kuiper Belt Object (KBO) due to its retrograde orbit and similarity in composition to other KBOs like Pluto. The flyby of Voyager 2 in 1989 revealed a satellite with a paucity of craters, suggesting a young surface, intriguing “cantaloupe terrain” of dimples and overlapping ridges, and active geyser-like plumes. Ground-based observations have found the surface to be predominantly nitrogen ice, along with some methane and carbon monoxide ices, with water and carbon dioxide ices forming a non-volatile bedrock.

To better understand the geological history of Triton, Davide Sulcanese of D’Annunzio University in Italy led a team using Voyager imagery and a digital elevation model to produce a geomorphological map of the Monad Regio area. The team better delineated previously mapped geological boundaries and described several new units, focusing on identifying cross-cutting relationships between units, which indicate relative ages. They conclude that in Triton’s early history, the surface was shaped by interior processes such as faulting and cryovolcanism, which segregated the surface into major regions such as cantaloupe, terraced, and knobby terrains. However, the moon then shifted into a phase of surficial processes, evinced by geomorphologies similar to moraines, ogives, U-shaped valleys, and channel systems on Earth. This suggests a late Triton dominated by glacial and fluvial processes that weathered and smoothed the preexisting terrain, thereby rejuvenating the surface.

Similar geomorphological features to those mapped have also been observed in the equatorial region of Pluto. When New Horizons visited Pluto in 2015, it revealed a diverse body replete with scientific intrigue. Voyager 2 remains the only spacecraft to visit Triton, but it only studied 40% of its surface. These icy worlds in the far reaches of the solar system likely retain discoveries waiting to be made. LEARN MORE