Сатурнның магнит өрісі және күн желтопарасы

Cavity in the solar wind the sixth planet creates
infobox magnetosphere
|background=paleturquoise
|image=
|caption=Aurorae on the south pole of Saturn as viewed by Hubble
|name=Saturn
|Field strength=21 μT (0.21 G)
|tilt=<0.5°
|Period=? |Radius=60,330 km
|field ref= The first evidence that Saturn might have an internally generated magnetic field came in 1974, with the detection of weak radio emissions from the planet at the frequency of about 1 MHz. These medium wave emissions were modulated with a period of about 10 h 30 min, which was interpreted as Saturn's rotation period. Nevertheless, the evidence available in the 1970s was too inconclusive and some scientists thought that Saturn might lack a magnetic field altogether, while others even speculated that the planet could lie beyond the heliopause. The first definite detection of the saturnian magnetic field was made only on September 1, 1979, when it was passed through by the Pioneer 11 spacecraft, which measured its magnetic field strength directly. This makes Saturn's magnetic field slightly weaker than Earth's; however, its magnetic moment is about 580 times larger. Saturn's magnetic dipole is strictly aligned with its rotational axis, meaning that the field, uniquely, is highly axisymmetric. The dipole is slightly shifted (by 0.037 Rs) along Saturn's rotational axis towards the north pole. As with Earth's magnetosphere, the boundary separating the solar wind's plasma from that within Saturn's magnetosphere is called the magnetopause. The magnetopause's position depends on the pressure exerted by the solar wind, which in turn depends on solar activity. The average magnetopause standoff distance is about 22 Rs. lies the bow shock, a wake like disturbance in the solar wind caused by its collision with the magnetosphere. The region between the bow shock and magnetopause is called the magnetosheath. At the opposite side of the planet, the solar wind stretches Saturn's magnetic field lines into a long, trailing magnetotail, Similar to Jupiter, the tail is the conduit through which the plasma of the internal magnetospheric origin leaves the magnetosphere. The innermost region co located with Saturn's planetary rings, inside approximately 3 Rs, has a strictly dipolar magnetic field. It is largely devoid of plasma, which is absorbed by ring particles, although the radiation belts of Saturn are located in this innermost region just inside and outside the rings. The fourth outermost region is located beyond 15 Rs at high latitudes and continues up to magnetopause boundary. It is characterized by a low plasma density and a variable, non dipolar magnetic field strongly influenced by the Solar wind. the magnetic field near the equatorial plane is highly stretched and forms a disk like structure called magnetodisk. Near the dayside it can be absent when the magnetosphere is compressed by the Solar wind, which usually happens when the magnetopause distance is smaller than 23 Rs. On the nightside and flanks of the magnetosphere the magnetodisk is always present.

The processes driving Saturn's magnetosphere are similar to those driving Earth's and Jupiter's. Just as Jupiter's magnetosphere is dominated by plasma co–rotation and mass–loading from Io, so Saturn's magnetosphere is dominated by plasma co–rotation and mass–loading from Enceladus. However, Saturn's magnetosphere is much smaller in size, while its inner region contains too little plasma to seriously distend it and create a large magnetodisk.#tag:ref|On the dayside a noticeable magnetodisk only forms when the Solar wind pressure is low, and the magnetosphere has a size larger than about 23 Rs. However, when the magnetosphere is compressed by the Solar wind the dayside magnetodisk is quite small. On the other hand, in the dawn sector of the magnetosphere the disk like configuration is present permanently.

The plasma composition in Saturn's inner magnetosphere is dominated by the water group ions: O+, H2O+, OH+ and others, hydronium ion (H3O+), HO2+ and O2+, although protons and nitrogen ions (N+) are also present. The main source of water is Enceladus, which releases 300–600 kg/s of water vapor from the geysers near its south pole. At least 100 kg/s of this water is eventually ionized and added to the co–rotating magnetospheric plasma. The Cassini spacecraft also observed small amounts of N+ ions in the inner magnetosphere, which probably originate from Enceladus as well. In the outer parts of the magnetosphere the dominant ions are protons, which originate either from the Solar wind or Saturn's ionosphere. Titan, which orbits close to the magnetopause boundary at 20 Rs, is not a significant source of plasma. For both Jupiter and Saturn, transport of plasma from the inner to the outer parts of the magnetosphere is thought to be related to interchange instability. Then, magnetic flux tubes loaded with this newly cold, water–rich plasma interchange with flux tubes filled with hot plasma arriving from the outer magnetosphere. The plasmoids move down the tail and escape from the magnetosphere. In the magnetodisk region, beyond 6 Rs, the plasma within the co–rotating sheet exerts a significant centrifugal force on the magnetic field, causing it to stretch.#tag:ref|The contribution of the plasma thermal pressure gradient force may also be significant. In addition, an important contribution to the ring current is provided by energetic ions with energy of more than about 10 keV. although it increases the total magnetic moment of the planet and causing the size of the magnetosphere to become larger. The aurorae usually look like bright continuous circles (ovals) surrounding the poles of the planet. the average position is 75 ± 1° for the southern aurora, while the northern aurora is closer to the pole by about 1.5°. From time to time either aurorae can assume a spiral shape instead of oval. In this case it begins near midnight at a latitude of around 80°, then its latitude decreases to as low as 70° as it continues into the dawn and day sectors (counterclockwise). In the dusk sector the auroral latitude increases again, although when it returns to the night sector it still has a relatively low latitude and does not connect to the brighter dawn part.]] Unlike Jupiter's, Saturn's main auroral ovals are not related to the breakdown of the co–rotation of the plasma in the outer parts of the planet's magnetosphere. The Saturnian aurorae are more similar to those of the Earth, where they are also Solar wind driven. Their location and brightness strongly depends on the Solar wind pressure: the aurorae become brighter and move closer to the poles when the Solar wind pressure increases. Thus the SKR is related to the auroras around the poles of the planet. The radiation itself comprises spectrally diffuse emissions as well as narrowband tones with bandwidths as narrow as 200 Hz. In the frequency–time plane, arc like features are often observed, much like in the case of the Jovian kilometric radiation. The modulation of the radio emissions by planetary rotation is traditionally used to determine the rotation period of the interiors of fluid giant planets. In the case of Saturn, however, this appears to be impossible, as the period varies at the timescale of ten years. In 1980–1981 the periodicity in the radio emissions as measured by Voyager 1 and 2 was 10 h 39 min 24 ± 7 s, which was then adopted as the rotational period of Saturn. Scientists were surprised when Galileo and then Cassini returned a different value—10 h 45 min 45 ± 36 s.

Saturn has relatively weak radiation belts, because energetic particles are absorbed by the moons and particulate material orbiting the planet. Saturn, however, has the second radiation belt discovered by Cassini in 2004 and located just inside the innermost D Ring. This belt probably consists of energetic charged particles formed via the CRAND process or of ionized energetic neutral atoms coming from the main radiation belt. Nevertherless the high energy particles cause weathering of the surfaces of the icy moons and sputter water, water products and oxygen from them.

The abundant population of solid bodies orbiting Saturn including moons as well as ring particles exerts a strong influence on the magnetosphere of Saturn. The plasma in the magnetosphere co rotates with the planet, continuously impinging on the trailing hemispheres of slowly moving moons. The absorption of energetic electrons and ions reveals itself by noticeable gaps in the radiation belts of Saturn near the moon's orbits, while the dense rings of Saturn eliminate all energetic electrons and ions closer than 2.2 RS, creating a low radiation zone in the vicinity of the planet. The three moons mentioned above add new plasma into the magnetosphere. By far the strongest source is Enceladus, which ejects a fountain of water vapor, carbon dioxide and nitrogen through cracks in its south pole region. Dione is the third moon producing more new plasma than it absorbs. The mass of plasma created in the vicinity of it (about 6 g/s) is about 1/300 as much as near Enceladus. This is the opposite to what is observed for the plasma absorbing moons. The plasma and energetic particles present in the magnetosphere of Saturn, when absorbed by ring particles and moons, cause radiolysis of the water ice. Its products include ozone, hydrogen peroxide and molecular oxygen. The first one has been detected in the surfaces of Rhea and Dione, while the second is thought to be responsible for the steep spectral slopes of moons' reflectivities in the ultraviolet region. A fraction of the oxygen gets ionized, creating a small population of O2+ ions in the magnetosphere. The SKR is powerful enough to be detected from a spacecraft at the distance of several astronomical units from the planet. Ulysses discovered that the period of the SKR varies by as much as 1%, and therefore is not directly related to the rotation period of the interior of Saturn.