The planet Uranus, interesting facts about the existence of which were first discovered in 1781 by the English scientist W. Herschel, is still being studied today. The astronomer kept under observation for several days a luminous body that had not previously been noticed in the starry firmament. In the course of calculations and reasoning, he finally came to the conclusion: the unidentified object is a new planet. The astronomy community suggested that Herschel name the planet after himself. But he modestly refused and proposed to name his brainchild in honor of King George III of England - George’s Planet. This idea was not accepted by society, and was named Uranus.
It is noteworthy that before the official discovery, scientists repeatedly noted the location of this planet in the galaxy. But they mistook it for a star, then for a comet, or even registered it as a star in the constellation Taurus.
Green star in the Universe
Uranus is the only planet named after the ancient Greek god who personified the heavens (usually Roman mythology was used). Uranus is located in 7th place in the solar system with a distance of 2.9 billion km from the star. Contains large amounts of methane in the clouds, which gives the planet a beautiful blue-green color.
There are 27 satellites hovering in the pitch darkness along with Uranus. All of them were named after the heroes of the works of W. Shakespeare and A. Pope. Among all the satellites, there are two largest:
- Oberon. The circumference of the satellite is 1520 km in diameter. It is located at a distance of about 582.6 thousand km from Uranus. One revolution around its planet takes 13 days, always turning one side towards it. The temperature of the ice giant does not exceed - 200˚С.
- Titania. The diameter of this satellite is 1580 km. It is separated from Uranus by 436 thousand km. It orbits its planet in 9 days. Titania is also cold, like Oberon, and has a temperature of -200 ̊C.
- The most incredible body that rotates in the orbit of Uranus is Miranda. With a diameter of 400 km, it has mountains up to 5 km in height and gorge of the same depth. In the area of the satellite's south pole there is a unique depression 15 km away.
Uranus is the third largest planet. Studies of its characteristics are carried out using the Voyager 2 spacecraft. Studying the parameters allows you to discover interesting facts about the planet Urani and learn a lot of new things about this celestial body:
The ring system of the planet deserves special attention. It has a complex structure consisting of a combination of internal and external groups of rings. In total, Uranus has 13 of them. They are not particularly bright and have a rather gloomy appearance. It is believed that the rings are the remains of a former satellite of Uranus. After destruction during a collision with the planet, particles of debris and dust remained in orbit, taking the form of circles. Given the age of the rings, it can be assumed that the disaster occurred relatively recently.
The study of the physical and chemical characteristics, rings and moons of Uranus is a long process. Astronomers have managed to accumulate a small amount of information about the cosmic body. Despite the fact that the planet Uranus is poorly studied, the information collected about it allows us to discover new things in the structure of the Solar system.
The story about Uranus for children contains information about what the temperature is on Uranus, about its satellites and features. You can supplement the message about Uranus with interesting facts.
Brief message about Uranus
Uranus is the seventh planet in the solar system that can be seen with the naked eye on a clear night. Named after the ancient Greek god of the sky. Like Earth, Uranus is called the blue planet - it is truly blue.
The atmosphere on Uranus consists mainly of hydrogen and helium, with a small admixture of methane. The upper layers of the atmosphere reflect blue rays, which gives the planet such a rich color.
Uranus orbits the Sun every 84 Earth years and is 20 times farther from the Sun than Earth. Therefore, Uranus is the coldest planet in the solar system, the surface temperature is -218 degrees. Just like other giant planets, Uranus has satellites and rings.
It is the fourth most massive planet in the solar system.
Message about the planet Uranus
Uranus is the bluest planet in the solar system. But the planet Uranus little studied.
Uranus, the first planet discovered in modern history, was discovered by chance by William Herschel while he was looking at the sky through his telescope on March 13, 1781.
The planet consists of different gases and ices. And the temperature on Uranus is about -220 degrees. A ray of sun at the speed of light reaches this planet in only 2-3 hours.
It makes a full revolution around its axis in 84 Earth years. Uranus is an icy giant planet. It is larger than the Earth 4 times and heavier at 14. At the center of the planet is a relatively small rocky core. And most of it is made up of an icy shell - the mantle. However, the ice there is not at all the same as we are used to seeing. It looks like a dense viscous liquid. On Uranus, it is impossible to determine where the clouds end and the surface begins.
Uranus rotates around its axis 17 o'clock. However, as on other giant planets, strong winds blow here, reaching speeds 240 meters per second. Therefore, some parts of the atmosphere overtake the planet and revolve around the planet in just 14 hours.
Winter on Uranus lasts almost 42 years and all this time the Sun does not rise above the horizon. That is, complete darkness reigns. This happens because Uranus rotates completely differently from other planets. Its axis is tilted so much that it “lies” on its side. If other planets can be compared to spinning tops, then Uranus is more like a rolling ball. Scientists suggest that a long time ago, Uranus collided with a small planet, which “dropped” it. And she herself became one of 13 rings of Uranus.
Like others giant planets, Uranus's atmosphere is primarily composed of hydrogen, helium, and methane, although their relative contributions are somewhat lower compared to Jupiter and Saturn.
The theoretical model of the structure of Uranus is as follows: its surface layer is a gas-liquid shell, under which there is an icy (a mixture of water and ammonia ice) mantle, and even deeper - a core of solid rock. Mass of the mantle and core amounts to approximately 85-90% of the total mass of Uranus. The solid matter zone extends to 3/4 of the radius of the planet.
The temperature in the center of Uranus is close to 10,000 K at a pressure of 7-8 million atmospheres (one atmosphere approximately corresponds to one bar). At the core boundary the pressure is approximately two orders of magnitude lower (about 100 kilobars).
The effective temperature, determined from thermal radiation from the surface of the planet, amounts to about 55 K.
Uranus was formed from initial solids and various ices (ice here should be understood not only as water ice), it consists of only 15% hydrogen, and there is almost no helium at all (in contrast to Jupiter and Saturn, which are mostly hydrogen ). Methane, acetylene and other hydrocarbons exist in much larger quantities than on Jupiter and Saturn. Mid-latitude winds on Uranus move clouds in the same directions as on Earth. These winds blow at speeds from 40 to 160 meters per second; on Earth, fast currents in the atmosphere move at a speed of about 50 meters per second.
Thick layer (haze) - photochemical smog- found around the sunlit pole. The sunlit hemisphere also emits more ultraviolet radiation. In this image of Uranus, the color contrast is artificially enhanced to highlight the difference between them.
Voyager's instruments detected a partly colder band between 15 and 40 degrees latitude, where temperatures are 2-3 K cooler.
Uranus' blue color results from the absorption of red light by methane in the upper atmosphere. Clouds of other colors probably exist, but they are hidden from observers by an overlying layer of methane. The atmosphere of Uranus (but not Uranus as a whole!) consists of approximately 83% hydrogen, 15% helium and 2% methane. Like other gas planets, Uranus has bands of clouds that move very quickly. But they are too poorly distinguishable and are visible only in high-resolution images taken by Voyager 2. Recent observations from HST have revealed large clouds. There is an assumption that this possibility arose in connection with seasonal effects, because as you might imagine, winter and summer on Uranus differ greatly: the entire hemisphere hides from winter for several years Sun! However, Uranus receives 370 times less heat from the Sun than Earth, so it doesn't get hot there in the summer either. In addition, Uranus emits no more heat than it receives from the Sun, therefore, most likely, it is cold inside.
The depletion of the planet's atmosphere in light gases is a consequence of the insufficient mass of the planet's embryo. During its formation, Uranus was unable to retain more hydrogen and helium near itself only because by the time the future Uranus assembled a sufficiently massive core, there was little free hydrogen and helium left in the Solar System. But Uranium contains more water, methane, and acetylene.
Uranus is a planet that is part of the solar system. It occupies the seventh position from the Sun and has the third largest radius among the planets of the Solar System. In terms of mass, this object ranks fourth.
The planet was first recorded in 1781 by the English astronomer William Herschel. It received its name in honor of the god of the sky in ancient Greece, Uranus, who was the son of Kronos and the grandson of Zeus himself.
It should be noted that Uranus is the first planet to be discovered in modern times using a telescope. This discovery was the first discovery of a planet since ancient times, expanding the known boundaries of the solar system. Despite the fact that the planet is quite large, it was previously seen from Earth, but was perceived as a star with a weak glow.
When comparing Uranus to gas giants such as Jupiter and Saturn, which are composed of helium and hydrogen, it lacks hydrogen in metallic form. The planet contains a lot of ice in various modifications. In this, Uranus is very similar to Neptune; scientists classify these planets into separate categories called “ice giants.” Still, the atmosphere of uranium consists of helium and hydrogen; not so long ago, methane and hydrocarbon additives were found in the atmosphere of the planet. The atmosphere has ice clouds that are composed of hydrogen and ammonia in solid form.
It should be noted that Uranus is the planet with the coldest atmosphere in the entire solar system. The lowest temperature recorded is −224 °C. Due to this, scientists believe that the planet’s atmosphere consists of several layers of clouds, in which the water horizon occupies the lower layers, and the upper layer is represented by methane. As for the interior of the planet, it consists of rocks and ice.
Like all the giants of the solar system, Uranus also has a magnetosphere and a system of rings around the planet. This object has 27 permanent satellites, which differ in diameter and orbits. A peculiarity of the planet is the horizontal position of the axis of rotation, due to this the planet lies on the side relative to the Sun.
Humanity received the first high-quality images of Uranus in 1986 using the Voyager 2 spacecraft. The images were taken at fairly close range and show a featureless planet with no visible cloud bands or storms. Modern research shows that the planet has seasonal changes in the atmosphere, and there are often storms with wind speeds of up to 900 km/h.
Discovery of the planet
Observation of Uranus began long before W. Herschel's discovery, because observers thought that it was a star. The first documented observations of the object date back to 1660, carried out by John Flamsteed. After this, in 1781, Pierre Monier, who observed the planet more than 12 times, studied the object.
Herschel is the scientist who first concluded that it was a planet and not a star. The scientist began his observations by studying the parallax of stars, and he used a telescope of his own making. Herschel made the first observation of uranium on March 13, 1781 in the garden near his own house in the city of Bath, which is located in Great Britain. At the same time, the scientist made the following entry in the journal: “near the star ζ of the constellation Taurus there is a nebulous star or comet.” After 4 days, the scientist made another note: “when searching for an observed star or comet, it turned out that the object had changed position, and this indicates that it is a comet.”
Further observations of the object at high magnification on a telescope showed the comet as a blurry spot that was faintly visible, although the surrounding stars were expressive and bright. Repeated studies said it was a comet. In April of the same year, the scientist received research from a colleague from the Royal Society of Astronomers, N. Maskelyne, who said that he had found neither a head nor a tail in this comet. Due to this, we can conclude that this is either a comet with a very elongated orbit, or another planet.
Herschel continued the description as a comet, but at the same time, most researchers suspected a different nature of the object. Thus, Russian astronomer A.I. Lexel calculated the distance to the object, which exceeded the distance from the Earth to the Sun and was equal to 4 astronomical units. Also, the German astronomer I. Bode suggested that the object discovered by Herschel could be a star that moves further than the orbit of Saturn, in addition, the scientist noted that the orbit of movement is very similar to planetary orbits. The final confirmation of the planetary nature of the object was made by Herschel in 1783.
For this discovery, Herschel was awarded a lifetime scholarship from King George III in the amount of 200 pounds, with one condition that the scientist move closer to the king so that he and his family could observe space objects through the scientist's telescope.
Planet name
Due to the fact that Herschel is the discoverer of the planet, he was awarded the honor of naming the planet by the royal community of astronomers. Initially, the scientist wanted to name the planet in honor of King George III as "George's Star", in Latin it is "GeorgiumSidus". This name was explained by the fact that at that time it was not relevant to name the planet in honor of an ancient god, in addition, this would answer the question of when the planet was discovered, to which it could be answered that the discovery falls during the government of King George III .
There was also a proposal from the French scientist J. Landa to name the planet in honor of the discoverer. There have been proposals to name it after the mythological wife of Saturn, namely Cybele. The name Uranus was proposed by the German astronomer Bode, who motivated the name by the fact that this god was the father of Saturn. A year after Herschel’s death, the original name “George” was almost never found anywhere, although in Great Britain the planet was called that way for about 70 years.
The name Uranus was finally assigned to the planet in 1850, when it was enshrined in His Majesty’s almanac. It should be noted that Uranus is the only planet whose name is taken from Roman mythology, and not from Greek.
The rotation of the planet and its orbit
The planet Uranus is 2.8 billion kilometers away from the Sun. The planet makes a full revolution around the Sun in 84 Earth years. Uranus and the Earth are separated from 2.7 to 2.85 billion years. The semi-axis of the planet's orbit is 19.2 AU. which is equal to almost 3 billion kilometers. At this distance, solar radiation is equal to 1/400 of the Earth's orbit. The orbital elements of Uranus were first explored by Pierre Laplace. Additional refinements to the calculations were made by John Adams in 1841; he also clarified the gravitational effect.
The period during which Uranus rotates around its own axis is 17 hours and 14 minutes. Like all giant planets, Uranus produces powerful winds that blow parallel to the planet’s rotation. These wind speeds reach 240 m/s. Because of this, some parts of the atmosphere located in southern latitudes make a full revolution around the planet in 14 hours.
Axis tilt
A peculiarity of the planet is the inclination of the rotation axis to the orbital plane; this inclination is equal to an angle of 97.86°. Due to this, when the planet rotates, it lies on its side and rotates retrograde. This position distinguishes the planet from others; the seasons here occur in a completely different way. The rotation of all the planets of the solar system can be compared to the movement of a top, and the rotation of Uranus is more similar to a rolling ball. Scientists suggest that such a tilt of the planet was due to the collision of the planet with a planetesimal during the formation of Uranus.
At the solstice on Uranus, one of the poles is turned completely towards the Sun, while at the equator there is a very rapid change of day and night, and the sun's rays do not reach the opposite pole. After half of the Uranian year, the opposite situation occurs, as the planet turns to the Sun with its other pole. An interesting fact is that each of the poles of Uranus is in complete darkness for 42 Earth years, and then illuminated by the Sun for 42 years.
Despite the fact that the poles of the planet receive the maximum amount of heat, the temperature at the equator is constantly higher. Why this happens is still unknown to scientists. Also, the position of the axis remains a mystery; scientists have put forward only a few hypotheses, which have not been confirmed by scientific facts. The most popular hypothesis for the tilt of Uranus's axis is that during the formation of the planets of the solar system, a so-called protoplanet crashed into Uranus, which was approximately the same size as the Earth. But this does not explain why not a single satellite of the planet has such an axis tilt. There is also a theory according to which the planet had a large satellite that rocked the planet’s axis, and later it was lost.
Visibility of the planet
For more than ten years, from 1995 to 2006, the visual magnitude of the planet Uranus fluctuated from +5.6m to +5.9m, this made it possible to contemplate the planet from Earth without the use of optical instruments. At this time, the angular radius of the planet fluctuated from 8 to 10 arc seconds. When the night sky is clear, Uranus can be detected with the naked eye; when using binoculars, the planet is visible even from urban areas. Observing the object using an amateur telescope, you can see a pale blue disk that has darkening around the edges. Using powerful telescopes with a lens of 25 centimeters, you can see even the largest satellite of the planet called Titan.
Physical characteristics of Uranus
The planet is 14.5 times heavier than Earth, while Uranus is the least massive of all the giant planets that are part of the Solar System. But the density of the planet is insignificant and equal to 1.270 g/cm³, which allows it to take second place among the planets with the lowest density after Saturn. Despite the fact that the diameter of the planet is larger than that of Neptune, the mass of Uranus is still less. This in turn confirms the hypothesis put forward by scientists that Uranus consists of ices of methane, ammonia and water. Helium and hydrogen in the planet's composition occupy an insignificant part of the main mass. According to scientists' hypotheses, rocks form the core of the planet.
Speaking about the structure of Uranus, it is customary to divide it into three main components: the inner part (core) is represented by rocks, the middle one consists of several icy shells, and the outer one is represented by a helium-hydrogen atmosphere. Approximately 20% of the radius of Uranus falls on the planet's core, 60% on the icy mantle, and the remaining 20% is occupied by the atmosphere. The core of the planet has the highest density, where it reaches 9 g/cm³; in addition, this area has high pressure, reaching 800 GPa.
It is necessary to clarify that ice shells do not have the generally accepted physical form of ice; they consist of a dense liquid that has a very high temperature. This substance is a mixture of methane, water and ammonia, it has excellent electrical conductivity. The described structure scheme is not clearly accepted and 100% proven; therefore, other options for the structure of Uranus are put forward. Modern technology and research methods cannot unambiguously answer all questions that interest humanity.
Nevertheless, the planet is usually perceived as an oblate spheroid, which has a radius at the poles of about 24.55 and 24.97 thousand kilometers.
A special feature of Uranus is also its significantly lower internal heat levels than other giant planets. Scientists have not yet been able to figure out the reason for the low heat flow of this planet. Even the similar and smaller Neptune emits 2.6 times more heat into space than it does from the Sun. The thermal radiation of Uranus is very weak and reaches 0.047 W/m², which is 0.075 W/m² less than what the Earth emits. More detailed studies have shown that the planet emits about 1% of the heat it receives from the Sun. The lowest temperatures on Uranus were recorded at the tropopause and are equal to 49 K, this indicator makes the planet the coldest in the entire solar system.
Due to the absence of large thermal radiation, it is very difficult for scientists to calculate the temperature of the planet’s interior. Nevertheless, hypotheses are put forward about the similarity of Uranus to other giants of the solar system; in the depths of this planet there may be water in a liquid state of aggregation. Due to this, we can conclude that the existence of living organisms is possible on Uranus.
Atmosphere of Uranus
Despite the fact that the planet does not have the usual solid surface, it is quite difficult to talk about distribution into the surface and atmosphere. Still, the most distant part from the planet is considered the atmosphere. According to preliminary calculations, scientists should assume that the atmosphere is 300 kilometers away from the main part of the planet. The temperature of this layer is 320 K at a pressure of 100 bar.
The corona of Uranus' atmosphere is twice the planet's diameter from the surface. The planet's atmosphere is divided into three layers:
- The troposphere, with a pressure of about 100 bar, occupies a range from -300 to 50 kilometers.
- The stratosphere has a pressure from 0.1 to 10−10 bar.
- The thermosphere, or corona, is 4-50 thousand kilometers away from the surface of the planet.
The atmosphere of Uranus contains substances such as molecular hydrogen and helium. It should be noted that helium is not located in the middle of the planet, like other giants, but in the atmosphere. The third main component of the planet's atmosphere is methane, which can be seen in the infrared spectrum, but its proportion decreases significantly with altitude. The upper layers also contain substances such as ethane, diacetylene, carbon dioxide and carbon monoxide, and particles of water vapor.
Rings of Uranus
This planet has a whole system of rings that are weakly defined. They consist of dark particles of very small diameter. Modern technologies have allowed scientists to become more familiar with the planet and its structure, and 13 rings have been recorded. The brightest is the ε ring. The planet's rings are relatively young; this conclusion can be made due to the small distance between them. The formation of the rings took place in parallel with the formation of the planet itself. There are suggestions that the rings could be formed from particles of Uranus' satellites that were destroyed during a collision with each other.
The first mention of rings was made by Herschel, but this is doubtful, since for two centuries no one had seen rings around the planet. Official confirmation of the presence of rings in Uranus was made only on March 10, 1977.
Moons of Uranus
Uranus has 27 permanent natural satellites, which differ in diameter, composition and orbit around the planet.
The largest natural satellites of Uranus:
Umbriel;
The names of the planet's satellites were selected from the works of A. Pope and W. Shakespeare. Despite the large number of satellites, their total mass is very small. The mass of all the satellites of Uranus is half less than the mass of Triton, the satellite of Neptune. Uranus's largest moon, Titania, has a radius of just 788.9 kilometers, which is half the radius of our Moon. Most satellites have a low albedo, due to the fact that they consist of ice and rock in a 1:1 ratio.
Among all the satellites, Ariel is considered the youngest, since its surface has the smallest number of impact craters from meteorites. And Umbriel is considered the oldest satellite. Miranda is an interesting satellite due to the large number of canyons up to 20 kilometers deep, which change into chaotic terraces.
Modern technologies do not allow humanity to find answers to all questions regarding Uranus, but still we already know a lot, and the research does not end there. In the near future, it is planned to launch spacecraft to the planet. NASA plans to launch a project in 2020 called Uranusorbiter.
Uranus is the coldest planet in the solar system, although not the most distant from the sun. This giant was discovered back in the 18th century. Who discovered it, and what are the satellites of Uranus? What's special about this planet? Read the description of the planet Uranus below in the article.
Peculiarities
It is the seventh most distant planet from the Sun. It is the third in diameter, it is 50,724 km. Interestingly, Uranus is 1,840 km larger in diameter than Neptune, but Uranus is less massive, which puts it in fourth place among the solar system heavyweights.
The coldest planet is visible with the naked eye, but a telescope with a hundredfold magnification will allow you to see it better. The moons of Uranus are much harder to see. There are 27 of them in total, but they are significantly removed from the planet and much dimmer than it.
Uranus is one of the four gas giants, and together with Neptune forms a separate group. According to scientists, the gas giants arose much earlier than the planets that are part of the terrestrial group.
Discovery of Uranus
Because it can be seen in the sky without optical instruments, Uranus has often been mistaken for a dim star. Before it was determined that it was a planet, it was observed in the sky 21 times. John Flamseed was the first to notice it in 1690, indicating it as star number 34 in the constellation Taurus.
William Herschel is considered the discoverer of Uranus. On March 13, 1781, he observed the stars with a man-made telescope, suggesting that Uranus was a comet or a nebulous star. In his letters, he repeatedly pointed out that on March 13 he saw a comet.
The news about the newly spotted celestial body quickly spread in scientific circles. Some said it was a comet, although some scientists had doubts. In 1783, William Herschel declared that it was, after all, a planet.
They decided to name the new planet in honor of the Greek god Uranus. All other names of the planets are taken from Roman mythology, and only the name of Uranus is from Greek.
Composition and characteristics
Uranus is 14.5 times larger than Earth. The coldest planet in the solar system does not have the solid surface we are accustomed to. It is assumed that it consists of a solid rock core covered with a shell of ice. And the top layer is the atmosphere.
The icy shell of Uranus is not solid. It consists of water, methane and ammonia and makes up about 60% of the planet. Due to the absence of a solid layer, difficulties arise in determining the atmosphere. Therefore, the outer gas layer is considered to be the atmosphere.
This shell of the planet is bluish-green due to its methane content, which absorbs red rays. It is only 2% on Uranus. The remaining gases that are included in the atmospheric composition are helium (15%) and hydrogen (83%).
Like Saturn, the coldest planet has rings. They were formed relatively recently. There is an assumption that they were once a satellite of Uranus, which broke up into many small particles. There are 13 rings in total, the outer ring has a blue light, followed by red, and the rest have a gray color.
Orbital movement
The coldest planet in the solar system is 2.8 billion kilometers away from Earth. The equator of Uranus is inclined to its orbit, so the rotation of the planet occurs almost “lying” - horizontally. It’s as if a huge ball of gas and ice is rolling around our star.
The planet orbits the Sun every 84 years, and its daylight hours last approximately 17 hours. Day and night change quickly only in a narrow equatorial strip. In other parts of the planet, the day lasts 42 years, and then the night lasts the same amount.
With such a long change in time of day, it was assumed that the temperature difference must be quite serious. However, the warmest place on Uranus is the equator, not the poles (even those illuminated by the Sun).
Climate of Uranus
As already mentioned, Uranus is the coldest planet, although Neptune and Pluto are located much further from the Sun. Its lowest temperature reaches -224 degrees on average
Researchers have noticed that Uranus is characterized by seasonal changes. In 2006, the formation of an atmospheric vortex on Uranus was noted and photographed. Scientists are just beginning to study the changing seasons on the planet.
It is known that clouds and wind exist on Uranus. As you approach the poles, the wind speed decreases. The highest wind speed on the planet was about 240 m/s. In 2004, from March to May, a sharp change in weather conditions was recorded: wind speed increased, thunderstorms began, and clouds appeared much more often.
The following seasons are distinguished on the planet: southern summer solstice, northern spring, equinox and northern summer solstice.
Magnetosphere and planetary research
The only spacecraft that managed to reach Uranus is Voyager 2. It was launched by NASA in 1977 specifically to explore the distant planets of our solar system.
Voyager 2 managed to discover new, previously invisible rings of Uranus, study its structure, as well as weather conditions. Until now, many of the known facts about this planet are based on data obtained from this device.
Voyager 2 also discovered that the coldest planet has a magnetosphere. It was noted that the planet's magnetic field does not emanate from its geometric center. It is tilted 59 degrees from the axis of rotation.
Such data indicate that Uranus’s magnetic field is asymmetrical, unlike Earth’s. There is an assumption that this is a feature of icy planets, since the second icy giant - Neptune - also has an asymmetric magnetic field.