July 2019
Jennifer Hanley
Neptune’s Moon Triton Fosters
Rare Icy Union
Observations from the visiting IGRINS spectrograph at Gemini
South reveal for the first time beyond the lab, an extraordinary
union between carbon monoxide and nitrogen ices. The discovery
offers insights into how this volatile mixture can transport material
across Neptune’s moon Triton via geysers, trigger seasonal
atmospheric changes, and provide a context for conditions on
other distant, icy worlds.
Neptune’s largest moon Triton has been mysterious ever since its discovery
in 1846 as the only large retrograde-orbiting satellite: in 1989, the Voyager 2
flyby (Figure 1) showed geologic activity despite extremely cold temperatures,
and later ground-based observations showed it and Pluto sharing similar sur-
face compositions. Triton is now thought to be a captured dwarf planet from
the Kuiper Belt, but further observations are necessary to unmask the moon’s
many secrets.
Figure 1.
Voyager 2 image of Triton
showing the south polar
region with dark streaks
produced by geysers visible
on the icy surface.
Credit: NASA/JPL
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Until we can return to the Neptunian system (and there are proposals under-
way), our best way to understand Triton is through telescopic observations,
laboratory investigations, and chemical modeling. Our research at the As-
trophysical Materials Laboratory at Northern Arizona University in Flagstaff,
Arizona, has combined these techniques in order to study the composition
of Triton’s surface. For the telescopic observations, we utilized the visiting high-resolution
near-infrared spectrometer IGRINS — built as a collaboration between the University of
Texas at Austin and the Korea Astronomy and Space Science Institute (Park et al. , 2014;
Mace et al. , 2018) — which allowed us to acquire a high signal-to-noise spectrum of Triton
to make an unprecedented discovery beyond the lab. We recently published the synthesis
of these results in The Astronomical Journal (Tegler et al., 2019).
GeminiFocus
January 2020 / 2019 Year in Review