Neptune & Moons
- Neptune was not known to the ancients. It is not visible to the naked eye and was first observed in 1846. Its position was determined using mathematical predictions. It was named after the Roman god of the sea.
- Neptune spins on its axis very rapidly. Its equatorial clouds take 18 hours to make one rotation. This is because Neptune is not solid body.
- Neptune is the smallest of the ice giants. Despite being smaller than Uranus, Neptune has a greater mass. Below its heavy atmosphere, Uranus is made of layers of hydrogen, helium, and methane gases. They enclose a layer of water, ammonia and methane ice. The inner core of the planet is made of rock.
- The atmosphere of Neptune is made of hydrogen and helium, with some methane. The methane absorbs red light, which makes the planet appear a lovely blue. High, thin clouds drift in the upper atmosphere.
- Neptune has a very active climate. Large storms whirl through its upper atmosphere, and high-speed winds track around the planet at up 600 meters per second. One of the largest storms ever seen was recorded in 1989. It was called the Great Dark Spot. It lasted about five years.
- Neptune has a very thin collection of rings. They are likely made up of ice particles mixed with dust grains and possibly coated with a carbon-based substance.
- Neptune has 14 moons. The most interesting moon is Triton, a frozen world that is spewing nitrogen ice and dust particles out from below its surface. It was likely captured by the gravitational pull of Neptune. It is probably the coldest world in the solar system.
- Only one spacecraft has flown by Neptune. In 1989, the Voyager 2 spacecraft swept past the planet. It returned the first close-up images of the Neptune system. The NASA/ESA Hubble Space Telescope has also studied this planet, as have a number of ground-based telescopes.
- Neptune’s Great Dark Spot The Great Dark Spot in the southern atmosphere of Neptune was first discovered in 1989 by the Voyager 2 spacecraft. It was an incredibly large rotating storm system with winds of upto 1,500 miles per hour, the strongest winds recorded on any planet. How such powerful winds were discovered on a planet so far from the sun is still considered a mystery to this day. Data from the Voyager 2 spacecraft also showed that the Great Dark Spot varied significantly in size during their brief pass of the planet. When Neptune was viewed by the Hubble Space telescope in 1994 the Great Dark Spot had vanished, although a different dark spot had appeared in Neptune’s northern hemisphere.
- Neptune’s Atmosphere. Neptune has an incredibly thick atmosphere comprised of 74% hydrogen, 25% helium and approximately 1% methane. Its atmosphere also contains icy clouds and the fastest winds recorded in the solar system. Particles of icy methane and minor gases in the extremities of the atmosphere give Neptune its deep blue color. The striking blue and white features of Neptune also help to distinguish it from Uranus. Neptune’s atmosphere is subdivided into the lower troposphere and the stratosphere with the tropopause being the boundary between the two. In the lower troposphere temperatures decrease with altitude however they increase with altitude in the stratosphere. Hydrocarbons form hazes of smog that appear in the entire upper atmosphere of Neptune and hydrocarbon snowflakes that form in Neptune’s atmosphere melt before they reach its surface due to the high pressure. © Space Facts.com
More information and facts about Neptune
Atmosphere Neptune’s upper atmosphere is composed of 80% hydrogen (H2), 19% helium and trace amounts of methane. Similar to Uranus, the blue coloration of Neptune is due in part to its atmospheric methane, which absorbs light having a wavelength corresponding to red. Unlike Uranus, Neptune is a deeper blue, and, therefore, some other atmospheric component must be present in the Neptunian atmosphere that is not found in Uranus’ atmosphere. Two significant weather patterns have been observed on Neptune. The first, seen during the Voyager 2 fly-by mission, are the Dark Spots. These are storms comparable to the Great Red Spot found on Jupiter. However, a difference between these storms is their duration. Whereas the Great Red Spot has lasted for centuries, the Dark Spots are much more shortly lived as is evident by their disappearance when Neptune was viewed by the Hubble Space Telescope just four years after the Voyager 2 fly-by. The second of the two weather patterns observed by Voyager 2 is the swiftly moving white storm system, nicknamed Scooter. This type of storm system, which is much smaller than the Dark Spots, also appears to be short-lived. As with the other gas giants, Neptune’s atmosphere is divided into latitudinal bands. The wind speed achieved in some of these bands is almost 600 m/s, the fastest known in the Solar System.
Interior The interior of Neptune, similar to that of Uranus, is made of two layers: a core and mantle. The core is rocky and estimated to be 1.2 times as massive as the Earth. The mantle is an extremely hot and dense liquid composed of water, ammonia and methane. The mantle is between ten to fifteen times the mass of the Earth. Although Neptune and Uranus share similar interiors, they are, however, quite distinct in one way. Whereas Uranus emits only about the same amount of heat that it receives from the Sun, Neptune emits nearly 2.61 times the amount of the sunlight it receives. To place this in perspective, the two planets’ surface temperatures are approximately equal, yet Neptune receives only 40% of the sunlight that Uranus does. Additionally, this large internal heat is also what powers the extreme winds found in the upper atmosphere.
Orbit & Rotation With the discovery of Neptune, the size of the known Solar System increased by a factor of two. With an average orbital distance of 4.50 x 109 km, it takes sunlight almost four hours and forty minutes to reach Neptune. Moreover, this distance also means that a Neptunian year lasts about 165 Earth years! Neptune’s orbital eccentricity of .0097 is second smallest behind that of Venus. This small eccentricity means that the orbit of Neptune is very close to being circular. Another way of looking at this is to compare Neptune’s perihelion of 4.46 x 109 km and its aphelion of 4.54 x 109 km and notice that this is a difference of less than two percent. Like Jupiter and Saturn, Neptune rotates very quickly as compared to the terrestrial planets. With a rotational period of a little over 16 hours, Neptune has the third shortest day in the Solar System. The axial tilt of Neptune is 28.3°, which is relatively close to the Earth’s 23.5°. What is amazing is that, even at such a far distance from the Sun, Neptune still experiences seasons (though more subtly) similar to those on Earth as a result of its axial tilt.
Rings Currently, Neptune is known to have thirteen moons. Of these thirteen only one is large and spherical in shape. This moon, Triton, is believed to have originally been a dwarf planet captured by Neptune’s gravitational field, and, thus, not a natural satellite of the planet. Evidence for this theory comes from Triton’s retrograde orbit of Neptune; that is, Triton orbits in the opposite direction that Neptune rotates. With a recorded surface temperature of -235° C, Triton is the coldest known object in the Solar System. Neptune has three major rings – Adams, Le Verrier and Galle. This ring system is much fainter than that of the other gas giants. In fact, some of the rings are so dim that it was believed at one time that they were incomplete. However, images from the Voyager 2 fly-bys show extremely faint rings. © The Planets.org
Overview Triton is the largest of Neptune's 13 moons. It is unusual because it is the only large moon in our solar system that orbits in the opposite direction of its planet's rotation―a retrograde orbit. Scientists think Triton is a Kuiper Belt Object captured by Neptune's gravity millions of years ago. It shares many similarities with Pluto, the best known world of the Kuiper Belt. Like our own moon, Triton is locked in synchronous rotation with Neptune―one side faces the planet at all times. But because of its unusual orbital inclination both polar regions take turns facing the Sun. Triton has a diameter of 1,680 miles (2,700 kilometers). Spacecraft images show the moon has a sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows. Triton consists of a crust of frozen nitrogen over an icy mantle believed to cover a core of rock and metal. Triton has a density about twice that of water. This is a higher density than that measured for almost any other satellite of an outer planet. Europa and Io have higher densities. This implies that Triton contains more rock in its interior than the icy satellites of Saturn and Uranus. Triton's thin atmosphere is composed mainly of nitrogen with small amounts of methane. This atmosphere most likely originates from Triton's volcanic activity, which is driven by seasonal heating by the Sun. Triton, Io and Venus are the only bodies in the solar system besides Earth that are known to be volcanically active at the present time. Triton is one of the coolest objects in our solar system. It is so cold that most of Triton's nitrogen is condensed as frost, giving its surface an icy sheen that reflects 70 percent of the sunlight that hits it. NASA's Voyager 2―the only spacecraft to fly past Neptune and Triton―found surface temperatures of -391degrees Fahrenheit (-235 degrees Celsius). During its 1989 flyby, Voyager 2 also found Triton has active geysers, making it one of the few geologically active moons in our solar system.
How Triton Got its Name Triton is named after the son of Poseidon (the Greek god comparable to the Roman Neptune). Until the discovery of the second moon Nereid in 1949, Triton was commonly known as simply "the satellite of Neptune." © SOLAR SYSTEM. NASA.gov
10 Interesting Facts about Triton
– Triton is named after a sea-godSomewhat fittingly, the moon was named after Triton, the son of the Greek sea-god Poseidon whose Roman equivalent was Neptune. However, the name Triton was only officially adopted many years after its discovery, and it was known simply as “the satellite of Neptune” until the discovery of Neptune’s second moon, Nereid, in 1949.
– Triton has a retrograde orbitWhile many moons in the solar system have retrograde orbits, Triton is unique in this regard because it is the largest moon to orbit its parent body in the wrong direction. By way of comparison, some of Jupiter’s and Saturn’s moons have retrograde orbits, but they are situated much further away from their planets, and are also much smaller, with the largest among these moons, Phoebe (a moon of Saturn), being only 8% as big, and 0.03% as massive as Triton.
– Triton will crash into NeptuneSince Triton is already orbiting Neptune at a distance that is smaller than the Earth-Moon distance, it is almost certain that tidal forces will cause the moon’s orbit to decay further, and at an increasing rate as the orbits decays. Computer modelling suggests that in about 3.6 billion years, Triton will cross Neptune’s Roche limit, which is the distance at which an object orbiting a massive body will break apart. In practical terms, the Roche limit is reached when tidal forces overcome the gravitational forces that hold an orbiting body together. It is expected that when Triton reaches this point, it will either collide with Neptune’s atmosphere, forming a complex ring system, or it will simply break up and fall into Neptune.
– Triton is likely a captured Kuiper Belt objectSince moons that have retrograde orbits cannot form in the same region as their primaries, the only explanation for Triton’s orbit is that it was captured from the Kuiper belt, a ring-shaped reservoir of small icy and/or rocky objects that remained after the formation of the solar system. The Kuiper belt extends from just inside the orbit of Neptune to a distance of about 50 astronomical units from the Sun and since Triton is almost identical in composition, size, mass, and temperature to Pluto (a known Kuiper belt object), it is almost certain that Triton was captured by Neptune in the distant past.
– Triton has few impact cratersOnly 179 impact craters have been positively identified on the 40% of Triton’s surface that has been mapped, which suggests that the surface of the moon is continually undergoing a process of modification. In fact, studies have shown that on cosmic time scales, Triton’s surface is almost “brand new”, with an estimated age of between 50 million and only 6 million years old. Moreover, Triton’s surface is almost as smooth as a billiard table, with the highest known elevation being only about 1,000 metres.
– Triton has ice volcanoesAlthough Triton has a crust of ice, the processes that produce the observed ice volcanoes are almost identical to those that produce hot, lava volcanoes on Earth. Triton’s entire known surface is crisscrossed by rift valleys and pressure ridges, which suggests an ongoing process of volcanic and tectonic activity, but instead of hot lava, the volcanoes on Triton spew water ice and ammonia as the result of endogenic geological processes, as opposed to fractures caused by violent impacts.
– Triton also has nitrogen geysersApart from ice volcanoes, Triton also features geysers of sublimated nitrogen, somewhat like the geysers on Earth that spout hot water. While there are not many nitrogen geysers on Triton, all are located close to the subsolar point, which suggests that sunlight is heating reservoirs of subsurface frozen nitrogen to the point where it sublimates, before bursting through the solid ice sheet that overlays the reservoir. One such geyser was observed to squirt nitrogen gas and entrap dust to a height of 8,000 metres, and based upon this, it is estimated that each eruption could last for up to one earth-year, releasing the sublimated nitrogen gas of about 100 million cubic meters of frozen nitrogen.
– Triton features unique cantaloupe terrainKnown as “cantaloupe terrain” after its resemblance to the skin of a cantaloupe melon, this feature consists of closely linked depressions that can be as much as 30–40 km in diameter. While the formation consists primarily of water ice, its origin and process of formation remain uncertain, but it is certain that this area (which probably covers much of Triton’s western hemisphere), is not the result of impacts on account of the fact that the depressions show very little variation in terms of size and depth. However, one theory holds that the ridges are the result of “lumps” of dense, hard subsurface material that have somehow pushed through a softer and less dense top layer.
– Triton has a nearly perfectly circular orbitTriton’s orbit around Neptune is almost perfectly circular, with an eccentricity that is negligible. While there is some uncertainty how this came about in the relatively short history of the solar system, it is thought that factors such as gas drag from a substantial debris disc may have contributed significantly to the circularizing of Triton’s orbit.
– Triton’s surface is completely frozen overAlthough only about 40% of the moon’s surface is mapped, the percentage that is known is completely frozen over by a layer of frozen nitrogen, and it is extremely unlikely that the remaining 60% of Triton’s surface would be any different. The ice layer consists primarily of nitrogen ice, with water ice and frozen carbon dioxide completing the mix. The ice layer gives Triton a high albedo; it reflects between 60% and 95% of the light that falls onto it, while our own Moon only reflects about 11%-12% of light. © July 10, 2017 Peter Christoforou © Astronomy Trek.com