The surface of Neptune's moon Triton. Credit: NASA/JPL. Voyager 2 mission.

Neptune's largest moon accompanies the giant gas planet as it travels in an elliptical orbit around the Sun at an average distance of about 4,495,060,000 kilometers. Neptune requires approximately 165 Earth years to complete one revolution, so summer arrives at infrequent intervals on its near planet-sized moon.

On August 25, 1989, Voyager 2 became the first spacecraft to return close-up images of Neptune and its moons. Neptune is now officially recognized as the most distant planet from the Sun, since Pluto was voted to be a Kuiper Belt Object. It was during Voyager's flyby that six of Neptune's thirteen known moons were discovered.

Triton is in a retrograde orbit around Neptune, circling the planet opposite to the direction of its rotation, and is the only moon in the Solar System to exhibit that configuration. Most of its other moons are not visible from Earth, and little is known about them. About half are so close to Neptune that Earth-based telescopes are not able to resolve them against its background.

Triton is one of the Solar System's strangest moons. First, it has an atmosphere, cold and thin as it is. However, it shares that characteristic with only two others: Jupiter's moon Io, and Saturn's moon Titan. Triton's atmospheric pressure is greater than Io's but less than Titan's: only 1/100,000 that of Earth.

Second, its anomalous retrograde orbit could indicate that Triton is a captured body, but one that is unusually big. Triton is two-thirds the size of Earth's Moon. Third, its temperature makes it the coldest place known in the Solar System at -235 Celsius, yet so-called "nitrogen geysers" were seen spewing out of cracks in its surface. It is thought that those gas eruptions are what give Triton its atmosphere.

The geyser-like formations shooting nitrogen gas and dust particles eight kilometers into space were one of the Voyager mission's greatest surprises. They were called “ice volcanoes,” and several were identified in the south polar region.

Triton's surface features resemble those on Ariel, one of the moons circling Uranus; or those seen on Enceladus, one of Saturn's moons; as well as Jupiter's moons Europa, Ganymede, and Io. There are also polar ice caps similar to those on Mars, although Triton appears to most resemble Pluto in temperature, size, and chemical composition.

According to a recent press release, the European Southern Observatory (ESO) has used their Very large Telescope to perform an infrared analysis of Triton's atmosphere. Since Triton changes seasons once every forty years, this is the first time in over a century that summertime observations have even been possible.

The southern summer solstice began in 2000, and scientists think that the atmosphere has become much thicker since then due to the sublimation of ices off the moon's surface. Not just nitrogen, but carbon monoxide and methane have been detected in an upper layers of ice. They believe it is vapors from those thin layers, evaporated by the remote Sun, that have thickened the atmosphere.

The geysers, darkened cavities, and "wind streaks" on Triton have been explained as electric discharge effects in other locations. A previous Thunderbolts Picture of the Day noted an association with the bizarre “Dalmatian spots” and geysers on Mars. The apparent role of charged particle beams excavating ice, and provoking massive geyser activity was offered as a possible explanation:

“If the dark spotting on Mars’ south polar ice is indeed caused by charged particle streams, one of the first things we should look for is an active response of the surface to these events. Since the dark spotting is occurring in the Martian south polar spring, that would be the time to look for signs of energetic activity, not unlike the so-called 'volcanic' plumes of Jupiter’s closest moon Io, or the 'geysers' of Saturn’s moon Enceladus.”

Consensus scientists typically ignore electricity when observing events in Neptune’s frigid vicinity. They do not consider that similar formations on Io, Enceladus, or Mars are even relevant to the geological condition of Triton. They do not realize that those differences are not an issue when an electrical interpretation is considered.

Instead of the Sun's heat influencing the change of seasons on Triton, perhaps the orientation of the moon within the electric fields generated by its parent body should be considered.

Stephen Smith