In the lab, scientists have pinpointed a specific wavelength of infrared light absorbed when molecules of carbon monoxide and nitrogen join together and vibrate in unison. Individually, carbon monoxide and nitrogen ices each absorb their own distinct wavelengths, but the tandem vibration of their mixture absorbs at an additional, distinct wavelength. Now, astronomers using the 8-m Gemini South Telescope in Chile have recorded this same unique signature on Neptune’s largest moon Triton.
Voyager 2 image of Triton showing the south polar region with dark streaks produced by geysers visible on the icy surface. Image credit: NASA / JPL.
In the Earth’s atmosphere, carbon monoxide and nitrogen molecules exist as gases, not ices. In fact, molecular nitrogen is the dominant gas in the air we breath, and carbon monoxide is a rare contaminant that can be lethal.
On distant Triton, however, carbon monoxide and nitrogen freeze as ices. They can form their own independent ices, or can condense together in the icy mix detected in the Gemini data.
This icy mix could be involved in Triton’s iconic geysers first seen in images from NASA’s Voyager 2 spacecraft as dark, windblown streaks on the surface of the distant, icy moon.
“While the icy spectral fingerprint we uncovered was entirely reasonable, especially as this combination of ices can be created in the lab, pinpointing this specific wavelength of infrared light on another world is unprecedented,” said lead author Dr. Stephen Tegler, an astronomer at Northern Arizona University.
Voyager 2 first captured Triton’s geysers in action in the moon’s south polar region back in 1989.
Since then, theories have focused on an internal ocean as one possible source of erupted material.
Or, the geysers may erupt when the summertime Sun heats this thin layer of volatile ice on Triton’s surface, potentially involving the mixed carbon monoxide and nitrogen ice revealed by the Gemini observation.
That ice mixture could also migrate around the surface of Triton in response to seasonally varying patterns of sunlight.
“Despite Triton’s distance from the Sun and the cold temperatures, the weak sunlight is enough to drive strong seasonal changes on Triton’s surface and atmosphere,” said co-author Dr. Henry Roe, Deputy Director of Gemini Observatory.
“This work demonstrates the power of combining laboratory studies with telescope observations to understand complex planetary processes in alien environments so different from what we encounter every day here on Earth.”
The findings will be published in the Astronomical Journal.
