Scientists believe that Triton, Neptune's largest satellite, may be an "ocean world. Researchers speculate that Triton may have an ocean of liquid water beneath the solid crust of ice.
"If this is true, and if we can ever reach this ocean and find life, it would extend the habitable zone to the Kuiper Belt, not just to the inner solar system. This has profound implications for both our solar system and exoplanets," said Dr. Candice Hansen-Koharchek, a planetary scientist.
Triton is only the third known planetary body in the solar system to have volcanic activity, besides Earth and Jupiter's moon Io. Unlike the geysers of Enceladus, which are believed to be caused by tidal heating, Triton's geysers are the result of solar heating. The dim sunlight causes the frozen nitrogen on the moon's surface to slowly melt and eventually erupt. Active geology also explains the lack of craters on its surface.
"Triton has a nitrogen atmosphere that freezes seasonally in the polar caps," Dr. Hansen-Koharchek said. - "Earth also has an atmosphere made up mostly of nitrogen - can you imagine if our atmosphere froze in winter? But Triton's atmosphere is rarefied, with winds blowing and carrying particles across the surface."
"Voyager 2 is the only spacecraft to visit Triton back in 1989. Another NASA mission to study Triton, known as TRIDENT, was selected as a finalist in 2020, but was ultimately rejected in NASA's final selection round in 2021.
"TRIDENT would have established the existence of a subsurface ocean, the first step in exploring the oceanic world," Dr. Hansen-Koharchek said. - "TRIDENT would have a near-infrared spectrometer that would allow us to map the distribution of ice (N2, CH4, CO, CO2 and H2O) across the surface of Triton for the first time (Voyager had no near-infrared spectrometer, so all we know about composition is what we can see from Earth)."