Solar System > Neptune System > Planet Neptune
Satellites | Rings | Research | Photos
- Introduction
- Size, mass and orbit
- Composition and surface
- Moons of Neptune
- Atmosphere and temperature
- Neptune's rings
- History of the study
Neptune is the eighth planet from the Sun and the most distant planet in the Solar System. It is a gas giant and a representative of the category of solar planets of the outer system. Pluto has dropped out of the planetary list, so Neptune closes the chain.
It cannot be found without instruments, so it was found relatively recently. The close approach was observed only once during the flyby of Voyager 2 in 1989. Let's find out what planet Neptune is in interesting facts.
General information about the planet
After Pluto reverted to dwarf planethood, Neptune regained its title as the farthest planet from the Sun.
It rotates in an orbit in which the average state from the star is 4.5 billion km. Fun fact : At this distance, sunlight takes about 253 minutes to reach Neptune.
The distance from Earth to the most distant planet varies in the range from 4.3 to 4.553 billion km. Thus, over time, Neptune approaches and moves away by 253 million km. Because of such a large distance, people cannot observe the planet without special equipment. To see it, you need a telescope with a radius of at least 12.5 cm and a 200x magnification. But even in it the planet is visible only in the form of a small spot.
Neptune has a blue color. This is due to the large amount of methane contained in the atmosphere. The substance absorbs red colors present on the surface, making them invisible to the eye. The planet also boasts the fastest winds in the solar system. Hurricanes travel along it, the speed of which reaches 2400 km/h.
Upcoming Events
September 14: Neptune at opposition
On September 14, 2022 at 12:12 Moscow time (09:12 GMT) Neptune will reach opposition. This is the best time to view the outer planet because it is typically at its brightest and appears larger than usual during this period. At the time of opposition, Neptune will be among the stars of Aquarius and will have a magnitude of 7.8. The planet will rise in the east around sunset and will be visible throughout the night.
Neptune cannot be seen with the naked eye. The ice giant is about five times fainter than the faintest stars. To see this distant planet, use binoculars or a telescope.
December 1: Neptune ends retrograde
In June 2022, Neptune began retrograde motion, which is an optical illusion caused by differences in the orbital speed of the planets. The ice giant will complete its retrograde motion (from east to west) in the sky on December 1, 2022. Neptune's retrograde periods occur once a year and last about five months.
March 13: Neptune conjunct the Sun
On March 13, 2022, Neptune will conjoin the Sun. The planet will pass close to the Sun in the sky and will not be visible for several weeks. At the moment of closest approach, the distance between the blue planet and the Sun will be only 1° 07′. Moreover, during this period Neptune will be at its maximum distance from our planet.
Orbit and radius
Ratio of planet sizes (Neptune on the right)
Neptune's orbit is an almost perfect circle, and its eccentricity is only 0.011. Because of this, as we rotate around the Sun, the distance to it changes slightly relative to the total distance. The planet completes a full revolution around the star in 164.8 Earth years; its speed in space is approximately 5.45 km/s.
Interesting fact : the last New Year's Eve was on Neptune on July 12, 2011. Accordingly, the next one will come around 2176.
Like other planets, Neptune rotates on its axis, which is tilted 28.3 degrees. Because of this, there are seasons on the surface with characteristic changes in weather conditions. But here they last for 40 years.
A day on Neptune lasts 16 hours, which is how long it takes for the magnetic field to rotate 360 degrees. The polar axes make a full rotation in 12 hours, and the gas shell in 18. This difference in rotation contributes to the emergence of strong hurricanes.
Physical characteristics of the planet
The planet's atmosphere makes up approximately 20% of the total mass. Beneath it lies an icy surface similar in composition to uranium. Its main components are methane and ammonia, which are in a liquid state. Interestingly, this mixture is called ice only conditionally, due to its high density, because its temperature varies in the range of 1700-4700 degrees Celsius. The surface is a large boiling ocean.
In the depths of Neptune, at a depth of 7 thousand km, there is a core. It has a temperature of 5500 degrees Celsius and consists of silicon and iron salts. It is subject to a pressure of 7 megabars. Scientists have thoroughly studied the characteristics of the planet, obtaining exact values:
- weight – 1.0234*10'26 kg;
- equator diameter – 48682 km;
- area – 7.6408 billion square meters. km;
- volume – 62.54 trillion. cube km;
- average density 1.638 g/cm3;
- free fall acceleration – 11.2 m/s2.
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Since Neptune is a gas giant, many characteristics depend on the nature of its atmosphere and surface density.
Neptune
The eighth planet of the solar system is Neptune.
Neptune appears in the sky as a star of magnitude 7, 8 (inaccessible to the naked eye); at high magnification it looks like a greenish disk, devoid of any details.
Neptune moves around the Sun in an elliptical, close to circular (eccentricity - 0.009), orbit, inclination to the ecliptic plane 1 ° 46.4′; its average distance from the Sun is 30.058 times greater than that of the Earth, which is approximately 4500 million km. This means that light from the Sun reaches Neptune in a little over 4 hours. The length of a year, that is, the time of one full revolution around the Sun, is 164.8 Earth years with an average orbital speed of 5.4 km/s.
It was possible to clarify the diameter of Neptune, due to its small angular diameter (2″), only on April 7, 1967, when the planet, in its movement against the background of the starry sky, obscured one of the distant stars. According to the results of these measurements, the equatorial radius of the planet was 24,750 km, which is almost four times the radius of the Earth, and its own rotation is so fast that a day on Neptune lasts only 17.8 hours. The direction of rotation is straight. The compression of the planet is estimated at 1/60. The acceleration of gravity on the surface of Neptune is about 11 m/s2 (15% more than on Earth), the 2nd escape velocity at the surface of Neptune is 23 km/s.
Although the average density of Neptune, equal to 1.67 g/cm3, is almost three times less than that of the Earth, its mass, due to the large size of the planet, is 17.2 times greater than that of the Earth.
Neptune has a magnetic field whose strength at the poles is approximately twice that of Earth.
The effective temperature of the surface regions is about 38 K, but as it approaches the center of the planet it increases to 12-14•103 K at a pressure of 7-8 megabars.
Of all the elements on Neptune, hydrogen and helium predominate in approximately the same ratio as on the Sun: there are about 20 hydrogen atoms per helium atom. In the unbound state, there is much less hydrogen on Neptune than on Jupiter and Saturn. Other elements are also present, mostly light. On Neptune, as on other giant planets, multilayer differentiation of matter occurred, during which an extended ice shell was formed, like on Uranus. According to theoretical estimates, there is both a mantle and a core. According to calculated models, the mass of the core together with the ice shell can reach 90% of the total mass of the planet.
Neptune receives very little light and heat from the Sun due to its great distance from it, and also because the planet's atmosphere scatters up to 83% of the radiation incident on it into space. Neptune's spectrum shows strong absorption bands of methane (CH4), especially intense in the red region, which is why Neptune has a greenish color. The equilibrium temperature on the surface of the planet is -220° C. Radio measurements give about -160°; this temperature apparently refers to the subcloud layer and indicates the presence of the planet’s own heat. Signs of molecular hydrogen H are also found in Neptune's spectrum, however, the predominant element in the atmosphere is probably helium, as indicated by the relatively high average density of the planet. The atmospheric pressure at cloud level is estimated at 3 atm.
To date, 8 satellites of Neptune are known.
Neptune is the eighth planet from the Sun and the fourth largest among the planets. After the discovery of Uranus, astronomers noticed that its orbit did not comply with Newton's law of universal gravitation, undergoing constant deviations. This suggested the existence of another planet beyond Uranus, which could, with its gravitational attraction, distort the trajectory of the seventh planet. Mathematicians John Adams and James Challis calculated the approximate location of the planet in 1845. At the same time, the French astronomer Urban Le Verrier, having made a calculation, convinced him to start searching for a new planet. Le Verrier's calculations were so accurate that Neptune was found immediately, on the very first night of observations. Neptune was first observed by astronomers Galle and d'Arrest on September 23, 1846, not far from the positions independently predicted by the Englishman Adams and the Frenchman Le Verrier. This discovery was a triumph of computational astronomy. In Roman mythology, Neptune (Greek Poseidon) is the god of the sea. Neptune can be seen with binoculars (if you know exactly where to look), but even with a large telescope you can hardly see anything other than a small disk.
Neptune seen through a ground-based telescope. The bright areas at the top of the disk are clouds of methane ice that reflect sunlight well. The planet's semimajor axis is 30.02 AU. Neptune is very far from the Sun. The orbital period is 164.491 years. Since its discovery in 1846, it has not yet completed one full revolution. The orbit is almost circular: the eccentricity is e = 0.011. The inclination of the orbital plane to the ecliptic plane is 1°46´22″, the average orbital speed is 5.4 km/s, the period of rotation around the axis is 15.8 hours. The inclination of the equator to the orbital plane is 29.6°. The mass of the planet is 1.03∙1026 kg, i.e. 17 times the mass of the Earth. The radius of the planet is 24,764 km - about four Earth radii. Density ρ = 1.76 g/cm3, i.e. 1/3 of the Earth's density. The compression ratio is 2%. Gravity acceleration at the level of the planet's upper cloud layer: 11.2 m/s2. The temperature of Neptune's atmosphere is higher than that of Uranus and is about 60 K. Consequently, Neptune has its own internal heat source - it emits 2.7 times more energy than it receives from the Sun.
The structure and set of elements that make up Neptune are probably almost the same as on Uranus: various “ices” and solidified gases containing about 15% hydrogen and a small amount of helium. Unlike Jupiter and Saturn, Uranus and Neptune may not have a clear internal stratification. But most likely, Neptune has a small solid core, equal in mass to the Earth. Neptune's atmosphere is mostly hydrogen and helium with a small amount of methane (1%). Neptune's blue color is the result of the absorption of red light in the atmosphere by this gas - just like on Uranus. Neptune experiences strong winds parallel to the planet's equator, large storms and vortices. The planet has the fastest winds in the solar system, reaching 700 km/h. The winds blow on Neptune in a westerly direction, against the planet's rotation. It has been noticed that for giant planets the speed of flows and currents in their atmospheres increases with distance from the Sun. This pattern has no explanation yet.
The Great Dark Spot as seen by Voyager 2. One of Voyager 2's first discoveries was the Great Dark Spot in the southern hemisphere, about the size of Earth. Neptune's winds carried the Great Dark Spot westward at 300 m/s. The circulation time of the substance in it is 16 days. Voyager 2 also saw a smaller dark spot in the southern hemisphere and a small, intermittent white cloud. It may be a current rising from the lower to upper layers of the atmosphere, but its true nature remains a mystery. Observations at the space telescope named after. Hubble showed in 1994: The Great Dark Spot has disappeared! It either simply dissipated or was obscured by something in the atmosphere. A few months later, the space telescope named after. Hubble discovered a new Dark Spot in Neptune's northern hemisphere for the second time. This indicates that Neptune's atmosphere is changing very quickly.
Voyager 2 detected Neptune's magnetic field. The planet's magnetic pole is 47° away from the geographic pole. It is assumed that Neptune's magnetic field is excited in a liquid conducting medium, in a layer located at a distance of 13 thousand km from the center of the planet. And under the liquid layer is the solid core of Neptune. Neptune's magnetosphere is highly elongated.
Neptune's largest satellite is Triton. The satellite Triton, discovered in 1846 by William Lascelles, is larger than the Moon. The orbit around Neptune is reversed, so scientists believe that Triton was captured by Neptune from the Kuiper Belt. Almost all the mass of Neptune's satellite system is concentrated in Triton. It has a high density: 2 g/cm3.
Frozen lake? Scientists believe that this plain, measuring approximately 200 by 400 km, was formed as a result of the eruption of an “ice” volcano.
Rocks, craters, and dark stripes of volcanic origin were discovered on Triton. Voyager 2 took pictures of red ice on Triton and photographed blue ice made of frozen methane at the equator. The southern polar cap consists of nitrogen ice, and geysers shoot out from it to a height of several kilometers. The surface of the satellite is light and reflects about 80% of the incident solar rays. Triton has a rarefied nitrogen atmosphere (surface pressure is about 10 mm Hg). The temperature on Triton is –235°C.
Neptune's satellite Nereid, discovered in 1949 by Gerard Kuiper, moves in an orbit with the highest eccentricity among satellites - 0.75.
Rings in the form of arches were discovered around Neptune, which were photographed by Voyager 2. Interestingly, information about the possible rings of Neptune was initially obtained in 1995 when observing the occultation of stars by the planet. Calculations showed that the arches are complex vortices, which were called epitons.
The eighth planet from the Sun, Neptune was the first planet located through mathematical predictions rather than through regular observations of the sky. (Galileo recorded it as a fixed star during observations with his small telescope in 1612 and 1613.) When Uranus did not travel exactly as astronomers expected it to, the French mathematician, Urbain Joseph Verrier, proposed the position and mass of another as yet An unknown planet, which could cause the observed one, moves into the orbit of Uranus. After being ignored by French astronomers, Verrier sent his predictions to Johann Gottfried Galle at the Berlin Observatory, who found Neptune on his first night of searching in 1846. Seventeen days later, its largest moon, Triton, was also discovered.
Nearly 4.5 billion kilometers (2.8 billion miles) from the Sun, Neptune orbits the Sun once every 165 years. It is invisible to the naked eye due to its extreme distance from the Earth. Interestingly, due to Pluto's unusual elliptical orbit, Neptune is actually the farthest planet (including dwarf planets) from the Sun during a 20-year period outside of every 248 Earth years.
Evidence for partial arcs around Neptune first arose in the mid-1980's, when stellar occultation experiments were found to sometimes show an extra "blink" just before or after the planet's occulted star. Images by Voyager 2 in 1989 settled the issue when the ring system was found to contain several weak rings, the outermost of which, Adams, contains three prominent arcs now called Liberty, Equality and Fraternity. The existence of arcs is very difficult to understand, because the laws of motion would predict that arcs that extend into a uniform ring have very short timescales. The gravitational effects of Galatea, the moon just inward from the ring, are believed to enclose the arcs. Several other rings were discovered by the Traveler's cameras. In addition to the narrow Adams Ring 63,000 km from Neptune's center, the Leverrier Ring is 53,000 km and wider, and the fainter Galle Ring is 42,000 km away. The weak extension directed outward towards the Leverrier Ring was called Lassell; it is bounded at its outer edge by the 57,000 km Arago Ring.
We don't know what drink William Lascelles may have had to celebrate his discovery of Neptune's moon, Triton, but beer made it possible.
Lassell was one of England's top amateur astronomers of the 19th century, using the wealth he made in the brewery business to finance his telescopes. He identified Triton on October 10, 1846—only 17 days after the Berlin Observatory discovered Neptune.
Curiously, a week before he found the satellite, Lassell thought he saw a ring around the planet. This turned out to be a distortion caused by his telescope. But when NASA's Voyager 2 visited Neptune in 1989, it showed that the gas giant has rings, although they are far too faint for Lassell to see.
Since Neptune was named for the Roman god of the sea, its moon was named for various lesser sea gods and nymphs in Greek mythology.
Triton (not to be confused with Saturn's moon, Titan) is the distant and by far largest of Neptune's moons. Dutch - American Astronomer Gerard Kuiper (for whom the Kuiper Band was named) found Neptune's third-largest moon, Neried, in 1949. He missed Proteus, the second-largest, because it is too dark and too close to Neptune for telescopes of that erasure symbol. This slightly non-spherical moon is thought to be right on the limit of how massive an object can be before its gravity pulls it into a sphere.
Proteus and five other moons had to wait for Voyager 2 to make themselves known. All six are among the darker objects found in the solar system. Astronomers using improved ground-based telescopes found five more moons in 2002 and 2003, bringing the known total to 13.
Traveler 2 revealed some fascinating details regarding the Triton. Part of its surface resembles the crust of a cantaloupe. Ice volcanoes erupt what is likely a mixture of liquid nitrogen, methane, and dust, which immediately freezes and then snows retreat to the surface. One Voyager 2 image shows a frost plume shooting 8 km (5 miles) into the sky and drifting 140 km (87 miles) downwind.
Triton's icy surface reflects so much of what little sunlight reaches that the moon is one of the coldest objects in the solar system, around -240 C (-400 F).
It is the only large moon in the solar system that circles in front of its planet in a direction opposite to the planet's rotation (retrograde orbit), which says it may once have been an independent target that captured Neptune. The disruptive effect this would have on other moons could help explain why Nereid has the most eccentric orbit of any known moon—it's almost seven times as far from Neptune at one end of its orbit as at the other end.
Neptune's gravity acts as a drag on Triton's counter-orbit, slowing it down and making it drop closer and closer to the planet. Millions of years from now, Triton will come close enough for gravitational forces to break it apart—possibly forming a ring around Neptune bright enough for Lassell to see.
Neptune is the most distant planet of the gas giants. It has an equatorial diameter of 49,500 kilometers (30,760 miles). If Neptune had a floor, it could contain almost 60 Earths. Neptune orbits the Sun every 165 years. It has eight moons, six of which were found by the Traveler. A day on Neptune is 16 hours and 6.7 minutes. Neptune was discovered on September 23, 1846 by Johann Gottfried Galle, Berlin Observatory, and Louis d'Arrest, an astronomy student, through mathematical predictions made by Urbain Jean Joseph Verrier. The first two-thirds of Neptune is composed of a mixture of molten rock, water, liquid ammonia and methane. The outer third is a mixture of heated gases composed of hydrogen, helium, water and methane. Methane gives Neptune its blue cloud color.
Neptune is a dynamic planet with several large, dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot, known as the Great Dark Spot, is relative to the size of the earth and is similar to the Great Red Spot on Jupiter. The traveler showed a small, irregular, eastward-moving cloud shaped like scooting around Neptune every 16 hours or so. This scooter, as it was dubbed, could be a feather growing above a deeper cloud deck.
Long bright clouds, similar to cirrus clouds on Earth, have been seen high in Neptune's atmosphere. In low northern latitudes, Voyager captured images of cloud streaks leading to their shadows on cloud decks below.
The strongest winds on any planet have been measured on Neptune. Most of the winds there blow to the west, opposite the planet's rotation. Near the Great Dark Spot, winds photographically increase to 2,000 kilometers (1,200 miles) an hour.
Neptune has a set of four rings that are narrow and very faint. The rings are made up of dust particles thought to be made by tiny meteorites crashing into Neptune's moons. From the ground, the ring telescopes appear to be arcs, but from Voyager 2, the arcs turned out to be bright spots or clusters in the ring system. The exact cause of bright clusters is unknown.
Neptune's magnetic field, similar to that of Uranus, is highly inclined at 47 degrees from the axis of rotation and an offset of at least 0.55 radii (about 13,500 kilometers or 8,500 miles) from the physical center. By comparing the magnetic fields of the two planets, scientists think that the extreme orientation may be characteristic of the currents in the planet's interior and not the result of that planet's transverse orientation or any possible field reversals in either
Our knowledge of Neptune's internal structure is inferred from the planet's radius, mass, rotation period, shape of its gravitational field, and the behavior of hydrogen, helium, and water at high pressure. This cutaway view shows Neptune, composed of an outer envelope of molecular hydrogen, helium and methane, roughly a mass of one to two Earths. Below this region, Neptune appears to be composed of a mantle rich in water, methane, ammonia, and other elements. These elements are found under high temperatures and pressures deep within the planet. The mantle is equivalent to 10 to 15 Earth masses. Neptune's core is made up of rock and ice, and is probably no more than one Earth's mass.
These two 591-second exposures of Neptune's rings were received by Voyager 2 on August 26, 1989 at a distance of 280,000 kilometers (174,000 miles). The two main rings are clearly visible and appear complete over the imaged region. Also visible in this image is an inner faint ring about 42,000 kilometers (25,000 miles) from Neptune's center, and a faint band that extends smoothly from the 53,000 kilometer (33,000 miles) ring to roughly halfway between the two bright rings . Bright bright light in the crescent moon of Neptune. Numerous bright stars are evident in the background. Both rings are continuous.
Neptune's composition is similar to Uranus: various "ices" and rock with a small amount of helium and about 15% hydrogen. Like Uranus, Neptune does not have a distinct internal hierarchical structure, but rather is more or less homogeneous in composition. But there is probably a small core of rocky material inside it. Its atmosphere is mostly hydrogen and helium with a small amount of methane.
Neptune's blue color is the result of red light being absorbed by methane in the upper atmosphere.
Like any gas planet, winds blow at very high speeds on Neptune. Neptune's winds are the fastest in the solar system, reaching speeds of 2000 km/h.
Like Jupiter and Saturn, Neptune has an internal source of heat - it emits twice as much energy as it receives from the Sun.
During Voyager's mission, Neptune's most prominent feature was the Great Dark Spot in the southern hemisphere. Its size was approximately half the size of Jupiter's Great Red Spot (the size of Earth's diameter). Winds blowing across Neptune's surface moved the Great Dark Spot westward at 300 meters per second (700 mph). Voyager 2 also discovered a smaller dark spot in the southern hemisphere and a small irregular white cloud that passed around Neptune every 16 hours, now known as the Scooter. Its nature remains a mystery.
However, observations of Neptune in 1994 show that the Great Dark Spot has disappeared! It has either simply dissipated, or is constantly hidden under the atmosphere. A few months later, a new dark spot was discovered in Neptune's northern hemisphere. This indicates that Neptune's atmosphere is changing rapidly, possibly due to small changes in temperature differences between the cloud tops and bottom layers.
Neptune was discovered at the Berlin Observatory on September 23, 1846, by Johannes Galle, based on predictions made independently by John C. Adams in England and Urbain J. Leverrier in France. Their calculations relied on discrepancies between the observed and predicted orbits of Uranus since its discovery in 1781, which were attributed to gravitational disturbances of the unknown planet. General information about Neptune
One of the major planets in the Solar System, usually the eighth from the Sun (Between 1979 and 1999, Pluto's elongated orbit brought it closer to the Sun than Neptune.) Neptune, one of the four "gas giants", has a small a rocky core surrounded by an icy mantle of frozen water, methane and ammonia. The diameter of the planet is almost four times the diameter of the Earth. The outer atmosphere consists mainly of molecular hydrogen with the addition of helium (15-20% by weight) and a small amount of methane.
In the sky, Neptune is an object of the seventh or eighth magnitude, that is, it cannot be observed with the naked eye from Earth. Through a good telescope with high power, Neptune appears as a slightly bluish disk (this color is explained by the presence of methane in the planet's upper atmosphere). Surface details cannot be detected by ground-based optical instruments, although bright spots are observed in infrared light.
Close-up images of Neptune were taken from Voyager 2's flyby path in August 1989. Observations with the Hubble Space Telescope (HST) to discern features of Neptune's atmosphere began in 1994. In many respects (e.g., size and structure) Neptune is similar to Uranus. But unlike Uranus, Neptune's highly dynamic atmosphere contains noticeable and changing cloud structures. The most prominent structure discovered by Voyager 2 was named the Great Dark Spot. It turned out to be similar in nature to Jupiter's Great Red Spot. Located 20° south of the equator, it rotates counterclockwise with a period of about 16 days. Above it, as well as above other dark spots, bright “cirrus” clouds form. However, by 1994, when HST observations were made, the spot had completely disappeared. Meanwhile, another dark spot formed in the northern hemisphere of the planet, not noticed by Voyager. This spot was also accompanied by bright clouds. Subsequent HST observations showed that the cloud patterns were changing, although the overall structure of the atmosphere remained stable.
Neptune's upper atmosphere has two main layers of clouds. A layer of methane ice crystals lies on top of opaque clouds that may contain frozen ammonia or hydrogen sulfide. In addition, in the upper layers of the atmosphere there is a hydrocarbon haze resulting from the action of solar radiation on methane.
Regular radio bursts detected by Voyager 2 indicate that Neptune has a magnetic field and is surrounded by a magnetosphere. The bursts are separated by a time interval of 16.11 hours, which apparently corresponds to the rotation period of the planetary core. Atmospheric parts rotate at different speeds, and they shift along latitude. The measured wind speed was 2200 km/h. The planet's magnetic axis is inclined to the rotation axis at an angle of 47°, which suggests that the asymmetric field arises in the mantle, and not in the core.
Based on the total amount of energy emitted, the average temperature of the planet can be estimated at 59 K., but it remains unclear why Neptune emits 2.7 times more energy than it receives from the Sun.
Observations made from Earth during Neptune's occultations of other celestial bodies suggested the presence of incomplete ring "arcs". Voyager 2 discovered four small rings, one of which was “twinned” exactly as required to explain the occultation observations.
Neptune has a radius of 24,300 km (3.81 Earth radii), a mass of 17.2 Earth masses and an average density of 1.72 g/cm3. The rotation axis is tilted at an angle of 29°, and the planet rotates in a forward direction with a period of 17h48m, and orbits the Sun in almost 165 years. The closest and largest satellite, Triton, rotates with a period of 5d21h03m in the opposite direction in a circular orbit with a radius of 355,300 km, inclined to the equator of the planet by 159°. The satellite's diameter is estimated at approximately 3,500 km. The distant satellite, Nereid (diameter about 400 km), orbits in a forward direction every 360 days in a very elongated elliptical orbit with a semi-major axis of 5,510,000 km and an eccentricity of 0.75.
During Voyager 2's mission, six new moons were discovered around Neptune, bringing the total number of known moons (including Triton and Nereid) to eight.
Several more satellites have now been discovered.
Neptune, the eighth major planet in the solar system from the Sun, astronomical sign or. Discovered in 1846. Average distance to the Sun (semimajor axis of the orbit) 30.06 AU. e., or 4500 million km. The orbital eccentricity is 0.0086, the inclination to the ecliptic plane is 1°46.4′. N. makes a complete revolution around the Sun (sidereal period of revolution) in 164.79 years with an average orbital speed of 5.4 km/sec. It appears in the sky as (invisible to the naked eye) a 7.8 magnitude star with an angular diameter varying from 2.2” to 2.4”. At high magnification, it looks like a greenish disk, devoid of any details. The diameter of N. exceeds the equatorial diameter of the Earth by 3.88 times and is 49,500 km. Compression is estimated at 1/60. The volume of Earth is 57 times greater than the volume of the Earth. The mass is 17.28 Earth masses (1.03 × 1026 kg), the average density is 1.84 g/cm3. The acceleration of gravity on the surface of Earth is about 11 m/sec2 (15% more than on Earth), the 2nd escape velocity at the surface of Earth is 23 km/sec. The rotation period around the axis is 15.8 hours. The inclination of the Earth's equator to the orbital plane is 29°. N. has two satellites, one of which, Triton, discovered in 1846 by W. Lascelles, has a relatively large size (diameter about 4000 km) and moves backward in its orbit with a period of about 5.9 days. The second satellite, Nereid, discovered in 1949 by the American astronomer J.P. Kuiper, is a small body (300 km in diameter) orbiting the planet with a period of about a year (360 days).
N. receives very little light and heat from the Sun due to its great distance from it, and also because N.'s atmosphere scatters up to 83% of the radiation incident on it into space. In the spectrum of N. there are strong absorption bands of methane (CH4), especially intense in the red region, which is why N. has a greenish color. The equilibrium temperature of N is -220 °C. Radio measurements give about -160°; this temperature apparently refers to the subcloud layer and indicates the presence of the planet’s own heat. Signs of molecular hydrogen H are also found in N.'s spectrum; however, the predominant element in the atmosphere and interior of N. is probably helium, which is also indicated by the relatively high average density of the planet.
The discovery of R. is one of the most remarkable achievements of astronomy. Already two years after the discovery of the planet Uranus, in 1783, A. I. Leksel, who studied its movement and first calculated the elements of the orbit of this star, suggested that the observed irregularities in the movement of Uranus are caused by the attraction of an unknown planet orbiting at a greater distance from Sun. The search for such a planet at the end of the 1st half of the 19th century. took up J. Adams and W. Le Verrier, who followed similar paths completely independently of each other. In September 1845, Adams reported the results of his calculations, containing all the elements of the orbit and the position of the planet in the sky, to the director of the Greenwich Observatory, J. Erie, who became acquainted with Adams’ work only 9 months after receiving it and did not promptly organize a search for the unknown planet. Around the same time, Le Verrier calculated the elements of the orbit of the new planet and its place in the sky, which he reported on September 18, 1846 to the Berlin Astronomical Observatory. The planet was discovered by I. Galle on the first evening after receiving the letter, September 23, 1846; it was only 52′ from the predicted location.
Atmosphere
Photo of Neptune, where the atmosphere has a red glow
Like most planets in the solar system, Neptune's atmosphere is divided into layers. The troposphere is closest to the surface, followed by the stratosphere, thermosphere and exosphere.
Despite the fact that the surface of the celestial body is very hot, at the level of the troposphere the temperature drops to -220 degrees Celsius. Then, as you rise upward, it gradually increases, and in the thermosphere it is already 470 degrees.
The upper layers of the atmosphere consist of 80% hydrogen and 20% helium. Closer to the surface, methane appears, which gives the planet a bluish tint, ammonia and hydrogen sulfide.
Weather and climate
It is quite difficult for scientists to determine the average temperature of the planet, since in a particular area it can vary greatly over time. Neptune's core is heated to 5500 degrees Celsius, and the surface heats up from 1700 to 4700 degrees. Due to the asynchronous rotation of the planet and atmosphere, strong hurricanes arise. For example, since 1989, for five years, scientists have observed the Great Dark Spot, a powerful hurricane whose speed was 600 m/s and its size was 85.8 thousand km. Surface tornadoes are not uncommon. People see them once every few years. The last large vortex with a length of 9 thousand km was recorded in 2022.
Since the planet's axis of rotation is tilted, it regularly changes seasons, which last 40 years. Only on Neptune a specific season does not occur on the entire surface, but in a certain area. For example, in 2022, summer began in the northern part, and winter began in the southern part.
Raging winds
Snapshot of Neptune's winds
As mentioned above, hurricanes on Neptune are quite common. Winds fly over the surface with enormous speed, which averages 1000 km/h. Interestingly, they often move against the axis of rotation of the planet. Also, thanks to continuous observations, scientists were able to establish that the scale and speed of winds increase as Neptune moves away from the Sun. However, so far they cannot explain what this is connected with.
It is almost impossible to discern the presence of storms from Earth; only the Hubble telescope is capable of this, and even then under suitable conditions. Therefore, spacecraft are used for observation. The most famous is Voyager 2. It was launched in 1977, sending it away from the Sun. Its main task is to explore the distant planets of the system and try to get as far as possible into the depths of space. In 1989, Voyager 2 reached Neptune and took photographs. The photographs helped to better study the planet.
FAQ
Why is Neptune blue?
Neptune's methane atmosphere absorbs red light from the Sun and reflects blue light into space. As a result, the planet acquires a bright azure color.
How cold is it on Neptune?
Neptune, located at a great distance from the Sun, is one of the coldest places in the solar system. The average temperature on the planet is about −214 °C. The “hottest” place of the ice giant is its south pole, where the temperature is about −200 °C.
Why don't Pluto and Neptune collide?
Pluto's orbit is not in the same plane as the orbits of the eight planets in the solar system; The orbital planes of the dwarf planet and Neptune are steeply inclined to each other. In addition, Neptune and Pluto are in a 3:2 orbital resonance, which prevents the planets from approaching each other.
How did Neptune get its name?
Soon after the discovery of the new planet, Le Verrier proposed calling it Neptune. However, he later tried to name the ice giant Le Verrier after himself, which caused disapproval outside of France. In December 1846, Friedrich Georg Wilhelm von Struve, director of the Pulkovo Observatory in St. Petersburg, advocated the name Neptune, and it soon gained international recognition.
Why is Neptune denser than Saturn?
Neptune's density (1.638 g/cm^3) is greater than that of Saturn (0.687 g/cm^3), although the latter is larger in size. This is caused by differences in the ratio of hydrogen to helium in the planets' composition: Neptune has a lower ratio of hydrogen to helium than Saturn, and possibly includes a larger proportion of higher-density material such as rocky compounds.
What is the speed of the winds on Neptune?
Neptune boasts the strongest winds in the solar system, which can reach speeds of about 2,100 km/h. A famous storm discovered in 1989 by the Voyager 2 spacecraft in Neptune's southern hemisphere is called the Great Dark Spot. It disappeared by 1994, but a similar storm reappeared in 2016.
Magnetosphere
Image of Neptune's magnetosphere
Neptune's magnetic field consists of a dense shell that conducts current. Scientists have found that it has great power. The magnetic axis is shifted relative to the planetary rotation by 47 degrees, which is why hurricanes often appear on the surface. Neptune's magnetosphere also reflects solar winds, preventing them from corroding the atmosphere. Perhaps it is thanks to it that the planet maintains its characteristics unchanged.
A magnetic field
The location of Neptune's magnetic axis dramatically affects the properties and shape of the magnetic field. The axis is shifted from the center of the planet by half its radius. Its inclination to the axis of rotation is 47°. Therefore, the giant’s magnetosphere turns toward the solar wind flow, sometimes sideways, sometimes end-on.
As a result, magnetic field lines can be parallel or twisted into a bundle. Glows similar to the Earth's and polar ones sometimes appear above the planet But Neptunian auroras do not occur above the pole, but much lower.
Temperature on Neptune
Graphic layout of Neptune
Even though Neptune is far from the Sun, the planet is very hot. Its surface heats up to several thousand degrees Celsius, and scientists still cannot explain where this amount of heat comes from. The planet receives 60% less energy from the star than Uranus, so the high temperatures are clearly not due to the Sun.
Interesting fact : Neptune releases 2.61 times more energy into space than it receives from the Sun.
The most likely hypothesis for high temperatures on the planet is the presence of chemical reactions occurring in the lower layers of the atmosphere. For example, when methane breaks down into simple carbons, it can release heat. There is also an opinion that the source of energy is the radioactive core, in which various processes occur that contribute to heat release.
Interesting: Earth
