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Out of the handful of objects in our solar system that are still geologically active, the volcanic activity on Triton is perhaps the most peculiar. There are 13 regular and irregular moons orbiting Neptune, and Triton stands out from them all due to both its size and its retrograde orbit, meaning that it orbits Neptune in the opposite direction of the planet's rotation. With an icy surface of frozen nitrogen, Triton's crust is so intensely active with eruptions of ammonia lava and icy volcanoes that the impact craters that are commonly found on other moons are quickly erased by Triton's ever-changing geology. Here is a detailed look at what we know about volcanic activity on Triton to date.
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Discovery of Volcanic Activity on Triton
When the first clear images of Triton were sent back to Earth from the Voyager 2 interplanetary space probe in 1989, very little was known about the distant moon. Voyager 2 obtained data that revealed that the surface of Triton was remarkably flat and free of impact craters, which is one of the tell-tale signs of recent geological activity. The Voyager 2 also captured images of streaky formations that were formed by nitrogen geysers and plumes of gas and ice as high as 8 km (about 5 mi) that were erupting from active volcanoes. Most of the knowledge that we have developed regarding the volcanic activity on the surface of Triton is derived directly from analysis of data captured by Voyager 2 during its flyby.
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Cryovolcanism on Triton
Unlike the hot molten lava that we are familiar with here on Earth, the volcanoes of Triton give forth to eruptions of extremely frigid gas and ice spewing from Triton's frozen core. A cryovolcano is an icy volcano that emit plumes of very cold methane, ammonia and/or water. This volcanic activity is a result of melted ices that are caused by tidal friction or another source of heat. Triton's volcanic activity were the first cryovolcanoes discovered in our solar system when the Voyager 2 flew by the moon in 1989, but possible evidence of cryovolcanoes have also been observed on Europa, Miranda, Enceladus, Titan and, most recently, Pluto.
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Causes of Triton's Volcanoes
The frequent volcanoes and geysers on the surface of Triton indicates that this a relatively young moon that has a great deal of geologic activity beneath its crust. Interestingly, nearly all of the volcanic activity that has been observed on Triton occurs in the same general region of the moon's surface. Most of the volcanoes on Triton have been found between 50° and 57°S near the southern pole of this moon. This is the same area of the moon that receives the majority of solar radiation, and it appears that the modest amount of heat generated on Triton from the distant sun may play a key role in the volcanic activity on the moon.