Triton—Neptune’s Moon4 min read

Triton, the son of Poseidon (the Greek equivalent of the Roman God Neptune) in mythology, is the largest of the thirteen moons of Neptune that have been discovered.  It was discovered in 1846, a mere seventeen days after its planet was found, by the English astronomer William Lassell. It is one of the largest moons in the entire Solar System—it is around 1,700 miles, or about 2,700 kilometers, in diameter. It is approximately 2.8 billion miles away from the sun, and its average temperature is only a meager 38 Kelvin, or minus 235 degrees Celsius! This temperature is low enough to freeze nitrogen; hence, most of Triton is covered in nitrogen ice. However, what really sets Triton apart from its celestial counterparts is the fact that this satellite is geologically active—although just a few degrees away from the absolute zero, where all motion of atoms abruptly stops, the moon Triton is dramatic and alive with movement. In addition, this body rotates in a retrograde orbit (i.e. it rotates in a direction opposite to that of Neptune), and possesses a synchronous orbit with Neptune—which means that one side of the moon faces one side of the host planet at all times.

The crescent planet Neptune and its crescent moon Triton, as seen by NASA's Voyager 2 spacecraft in 1989. Credit: Voyager 2, NASA

The crescent planet Neptune and its crescent moon Triton, as seen by NASA’s Voyager 2 spacecraft in 1989.
Credit: Voyager 2, NASA

Astronomers had been spotting atmospheric haze and dark plumes of smoke emanating from the depths of Triton’s largest and farthest satellite, which were all travelling in the same direction—almost as if there were a powerful wind pulling these black smudges along; so, the astronomers set out to look for possible explanations to throw light on this inexplicable, mysterious event. Most of the surface features of this amazing entity were uncovered by the satellite Voyager 2 in 1989; the information received supported the belief that Triton’s surface is volcanically active. On incorporating this data, scientists theorized that these ice volcanoes and geysers on Triton could exist, and are fueled by the presence of liquid nitrogen. The configuration of the erupting plumes of smoke was described by Voyager Scientists, who stated that thin tendrils of smoke are ejected into the atmosphere of Triton for about five miles, and are then spread and dispersed into an elongated cloud—due to the power and force of the winds on this intriguing, bizarre satellite. As said by David Soderblom of the Space Telescope Science Institute, “the volcanoes on Triton seem to be a gentler version of the volcanoes on Earth”.

This type of volcanism is called cryogenic volcanism; a cryovolcano or ice volcano is a body that exists in extremely supercold temperatures, and erupts volatile substances such as water, moon dust, methane or ammonia, as opposed to the standard molten rock and lava. These erupted materials can be in either liquid or gaseous form, and consequently condense to solids when exposed to the low temperatures of the surrounding regions. As published in the Chicago Tribune, “Triton’s volcanism is very similar to that on Earth except it is icy. Instead of hot lava at 1,000 degrees, it has fluid ice at minus 300 degrees”. Essentially, the critical force behind the volcanoes on Triton’s surface is said to be the nitrogen below the body’s crust; when this nitrogen is exposed to the sun’s light over a prolonged period of time, as well as to its own internal heat, this liquid mushrooms into a violent gas that is spewed out through gaps in the moon’s surface. Just like the greenhouse effect observed on the earth, the nitrogen existing on Triton traps the little, weak amounts of internal and external heat it receives, and then uses it to create lines of cryovolcanoes—which shower the surface with molten ice.

The reason the discovery of active volcanoes upon Triton’s surface is so exciting is that this cosmic object was thought to be a dead, frozen, catatonic moon—because of the vast distance from the sun and its own planet. Amazing and awe-inspiring, Triton goes against the cosmic rules and presents itself with an amazing array of cryogenic, freezing volcanoes. And all in all, if active, almost psychedelic volcanos can exist billions of miles from a source of heat, does the cosmos have any limitations at all? A surreal world exists right here in the Solar System… so is anything in the universe too impossible or far-fetched to exist?

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