One of the coldest naturally occurring places in the Solar System, Neptune’s largest moon Triton has a tenuous atmosphere. At just a few dozen degrees above absolute zero, its unique conditions allow the formation of peculiar compounds. Now, an international team of researchers has discovered one of them thanks to its unique infrared fingerprint.
As reported in The Astronomical Journal, scientists have detected the presence of ice made of both carbon monoxide and nitrogen. The distant moon’s atmosphere is so cold that these compounds just freeze into a solid and sometimes they freeze together.
Even in a solid, molecules vibrate, and in this case, carbon monoxide and nitrogen vibrate in unison. The vibration leads to an emission of infrared light and this distinct signature was observed by the spectrometer on the Gemini South Telescope in Chile.
"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," lead author Professor Stephen Tegler, from Northern Arizona University, said in a statement.
The existence of this particular signature shows that these ices are not made of bits of carbon monoxide and bits of nitrogen. They are a compound in which carbon monoxide and molecular nitrogen are intimately mixed together.
The two compounds are very important for the moon. Together with methane, they are the main components of the tenuous atmosphere, which is 70,000 times less dense than Earth’s own. These compounds are thrown about in the atmosphere by geysers. The moon is geologically active with a liquid interior made of water and ammonia and geyser eruptions have been observed rising 8 kilometers (5 miles) high.
The discovery also has some exciting consequences when it comes to studying other cold bodies in the Solar System. Pluto and other objects in the Kuiper Belt might also be experiencing this strange mixing of ices. This type of observation might allow researchers to discover such compounds. Scientists believe this could provide new clues to the geological and atmospheric phenomena on these worlds.
Triton itself used to be a Kuiper Belt object before being captured by Neptune. We know this because it orbits in retrograde, meaning it goes against the rotation of the planet. It is the largest moon in the Solar System behaving in this way.