Now let’s build a ship to sail it.
A new day dawns on Triton. It’s going to be a cold one, much like the last. And the one before that… and every day since the moon settled into its present orbit around Neptune. Even the volcanoes here spew out cold gases and liquid water rather than hot magma. But below the frigid surface, which registers a temperature of -235 °C, there’s something more clement: a liquid ocean.
At first glance, Triton seems to be just another icy moon – a featureless, barren world spinning around Neptune, the outermost planet of our solar system. But Triton is different.
For one thing, it orbits Neptune backwards, moving in the opposite direction to Neptune’s rotation. It’s the only large moon in the solar system to do so. Satellites can’t form in these “retrograde” orbits, so Triton must have begun life elsewhere before being captured by the gas giant. It looks a lot like Pluto, and probably came from the same place – the inner edge of the Kuiper Belt, close to Neptune.
The Voyager 2 spacecraft flew past Triton in 1989, sending back images of the moon’s frozen surface. They revealed signs of cryovolcanism – the eruption of subsurface liquids which quickly freeze when exposed to the cold of the outer solar system. As such, Triton joins a short list of worlds in the solar system known to be geologically active.
Its surface ice is unique, too: largely composed of nitrogen, with some cantaloupe-textured terrain, and a polar cap of frozen methane.