Triton’s Haze Properties as Characterized in the Lab

Abstract:

Triton, the largest moon of the Neptune system, possesses a thin nitrogen atmosphere with trace amounts of carbon monoxide and methane. Therefore, Triton has similar atmospheric composition as well as temperature to that of the dwarf planet Pluto. Like both Pluto and Saturn's moon Titan, Triton has a haze layer thought to be composed of complex organics formed through hydrocarbon and nitrile photochemistry. Understanding the physical and chemical properties of these hazes is critical to understanding the radiative transfer, atmospheric evolution, and atmosphere-surface interactions of these outer solar system bodies. While Voyager 2 flew by Triton during its solar system Grand Tour, both Titan and Pluto have been explored more extensively with recent spacecraft missions. Triton is of great interest for future missions, both as a stand-alone object, an evolved representative of Kuiper Belt Objects, and as part of the larger Neptunian system.

We performed atmospheric chamber experiments in the JHU PHAZER (Planetary Haze Research) laboratory with trace amounts of carbon monoxide and methane in molecular nitrogen at 90 K under cold plasma discharge, generating Triton haze analogues, or Triton “tholin”. We then characterized the physical and chemical properties of these particles. We measured their bulk composition with combustion analysis, their molecular composition with very high resolution mass spectrometry, and their spectra from the optical to the near-infrared in both transmission and reflectance. We compare these properties to existing measurements of Triton's tenuous atmosphere and surface, as well as contextualize these results in view of all the small, hazy, nitrogen-rich worlds of our solar system.