The tilt between Neptune's magnetic and rotational axes, along with Triton's orbital obliquity, causes a strong time variability of the moon's local electromagnetic environment. To constrain Triton's interaction with the ambient magnetospheric plasma, we apply a hybrid (kinetic ions, fluid electrons) model including the moon's ionosphere and induced field. To represent the extremes in the changes to the local electromagnetic field over a synodic rotation, we consider two orientations between the ambient magnetic field and flow velocity. For each, we first investigate the (analytical) magnetic signatures associated with the superposition of Triton's induced field and the magnetospheric field in the absence of any plasma interaction effects. To constrain the effect of Triton's ionosphere on the currents, we model the interaction between the ionospheric and magnetospheric plasma in isolation from the moon's inductive response, before combining these effects to investigate the complex scenario of plasma interaction and induction. Finally, we explore the sensitivity of the plasma interaction to changes in the ambient plasma density and the strength of Triton's inductive response. Despite plasma interaction signatures that dominate the plasma perturbations far from the moon (beyond similar to 3 Triton radii), we illustrate that the induced field is clearly discernible within similar to 3 Triton radii, regardless of the moon's location within Neptune's magnetosphere. We find that the orientation of the magnetospheric field and velocity vectors strongly affects Triton's plasma interaction; at times, resembling those of Jupiter's or Saturn's moons, while at others, revealing unprecedented signatures that are likely unique to moons of the ice giants.

Spectra of Triton between 1.8 and 5.5 mu m, obtained in 2007 May and 2009 November, have been analyzed to determine the global surface composition. The spectra were acquired with the grism and the prism of the Infrared Camera on board AKARI with spectral resolutions of 135 and 22, respectively. The data from 4 to 5 mu m are shown in this Letter and compared to the spectra of N-2, CO, and CO2, i.e., all the known ices on this moon that have distinct bands in this previously unexplored wavelength range. We report the detection of a 4 sigma absorption band at 4.76 mu m (2101 cm(-1)), which we attribute tentatively to the presence of solid HCN. This is the sixth ice to be identified on Triton and an expected component of its surface because it is a precipitating photochemical product of Triton's thin N-2 and CH4 atmosphere. It is also formed directly by irradiation of mixtures of N-2 and CH4 ices. Here we consider only pure HCN, although it might be dissolved in N-2 on the surface of Triton because of the evaporation and recondensation of N-2 over its seasonal cycle. The AKARI spectrum of Triton also covers the wavelengths of the fundamental (1-0) band of beta-phase N-2 ice (4.296 mu m, 2328 cm(-1)), which has never been detected in an astronomical body before, and whose presence is consistent with the overtone (2-0) band previously reported. Fundamental bands of CO and CO2 ices are also present.