The planets the the outer solar mechanism are very different native those the the within solar system. The four Jovian or gigantic planets are much larger and also the distances in between them are much greater than the terrestrial planets. Likewise these planets room accompanied by extensive ring and satellite systems.

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To an exterior observer the outer planets would certainly be pertained to as the important component of the solar system, v the small chunks that rock and metal in the inner solar mechanism an insignificant feature of the all at once system.

An outline of the external Planets


There are 4 planets in the external solar system; the four Jovian planets – Jupiter, Saturn Uranus, and also Neptune. Pluto, i m sorry is more like among the satellites of the Jovian planets 보다 the Jovians us is now classified as a ‘dwarf planet.’ there are five officially known dwarf planets: Ceres, and the 4 “plutoids” – Pluto, Makemake, Haumea, and also Eris.

Jupiter and Saturn are so huge that even at their an excellent distance they appear as bright together the brightest stars. These 2 planets were known to the ancients, who plainly regarded them as important, offered the names bestowed. Uranus and Neptune were uncovered following the innovation of the telescope, as was Pluto.

Each of the huge planets has actually a mechanism of satellites and also rings, plenty of only recently found by spacecraft observations of the outer solar system. There will certainly doubtless it is in further enhancements to this team of objects. Saturn has actually a complicated ring system plus 62 recognized moons (53 named). Jupiter has actually 64 moons (50 named) and a pass out ring. Uranus has an complex system that narrow, dark rings, and also 27 satellites (all named). Neptune has actually a set of pass out rings and also 13 moons. Pluto has 4 known moons.

Chemistry of external Solar System

The ingredient of body found beyond the asteroid belt is really different indigenous that uncovered in the terrestrial bodies and their satellites. Beyond about 4 AU water ice had the ability to condense, and also was thus obtainable as a raw product in addition to the silicate rocks and metals found in the within solar system. Being written of hydrogen and also oxygen, two of the many abundant facets in the universe, a good deal the water ice most likely formed. Beyond 10 AU additional varieties of ices could additionally condense, however in smaller amounts than water ice.

Considering the solar nebula from which the solar system created as a whole, the materials available to kind a earth are as displayed in the table.

MaterialPercent through Mass
Hydrogen (H)77
Helium (He)22
Water (H2O)0.6
Methane (CH4)0.4
Ammonia (NH3)0.1
Rock and Metal0.3

A second significant difference is the result of the greater separation the the planets and also the build-up of huge cores of rock and ices. The arising cores the Jupiter and also Saturn became large enough the they were able to attract and also hold the hydrogen and helium from huge volumes the the solar nebula before it dissipated. Uranus and Neptune caught much much less hydrogen and helium, leading to their smaller sized size and different composition.

With the huge amounts of hydrogen accessible in the outer solar system, this is a reduce environment. Any oxygen current is merged with hydrogen to make water, and so it is unavailable to kind oxidized compounds with other elements. Therefore the compounds i beg your pardon are uncovered in the settings of the external planets are hydrogen-based: methane (CH4), ammonia (NH3), ethane (C2H6), and acetylene (C2H2), and also other complicated hydrocarbons.


Only 4 spacecraft have actually explored the outer solar system, all from the US. Exploration of this an ar presents a number of difficulties. The spacecraft have to be exceptionally reliable, since the trip times room years or decades. The craft must likewise be relatively autonomous, since the light-travel time come the external solar system is number of hours. The spacecraft must bring their own power sources since the sunshine is as well weak to power the craft through solar cells. Heaters are essential to keep instruments at suitable operating temperatures. Powerful radio transmitters and large antennae are needed to relay data earlier to Earth.


Pioneers 10 and 11 were introduced in 1972 and also 1973 together “trailblazers” come Jupiter, v the major objectives of determining even if it is the asteroid belt can be negotiated without damaging collision with little particles, and also the dangers of radiation in Jupiter’s magnetosphere. While the asteroid belt was successfully crossed, the high power plasma linked with Jupiter caused difficulties for onboard electronics. This details was invaluable for the architecture of succeeding missions. Pioneer 10 flew past Jupiter in 1974, and also sped towards the outermost get of the solar system. Pioneer 11 provided Jupiter’s gravity during its 1975 conference to command it towards Saturn which it flew by in 1979.

The mass of clinical studies that the external solar device were brought out by the Voyager 1 and 2 missions, launched in 1977. The Voyager probes carried 11 clinical instruments, consisting of camera, spectrometers, magnetometers, and devices to measure plasma attributes of the planetary magnetospheres. Voyager 1 reached Jupiter in 1979 and also then used a gravity help to send it come Saturn in 1980. Voyager 2 arrived at Jupiter 4 months later, and also then provided a different path to visit Saturn in 1981, Uranus in 1986, and also Neptune in 1989.

Voyager HomePage:

Galileo HomePage:

Cassini HomePage:

PlanetSpacecraftEncounter Date
JupiterPioneer 10Dec 73
Pioneer 11Dec 74
Voyager 1Mar 79
Voyager2Jul 79
UlyssesFeb 92
GalileoDec 95
CassiniDec 00
New HorizonsFeb 07
JunoJul 16
SaturnPioneer11Sep 79
Voyager 1Nov 80
Voyager 2Aug 81
Cassini/HuygensJul 04/Jan 05
UranusVoyager 2Jan 86
NeptuneVoyager 2Aug 89

The Voyager craft exploited a fairly rare alignment of the four Jovian planets all simultaneously on the exact same side of the sun, which only occurs every 175 year or so. Utilizing gravity assists on each flyby to direct the craft to the next planet encounter, all the outer planets other than Pluto have actually been visited.

The next step is the Galileo mission, launched in 1989. Galileo will check out Jupiter, Saturn, and also their satellites. Galileo arrived on Jupiter in 1995 and deployed an entry probe into Jupiter’s atmosphere prior to orbiting Jupiter for 3 years during which close encounters through the 4 Galilean moons will occur.

The Cassini mission launched in 1997 will use gravity assists to eventually send the Cassini probe to and also encounter through Saturn, the moons and also rings in 2004.

The Jovian Planets

Distance (AU)5.29.519.230.1
Period (yr)11.929.584.1164.8
Diameter (km)142,800120,54051,20049,500
Mass (Earth=1)318951417
Density (gm/cm3)
Rotation (hr)9.910.717.216.1
Basic Properties

Jupiter Page

Saturn Page

Uranus/Neptune Page

Images and also movies of external planets and also their satellites space at:

Note the distances and periods of rotation from the table.

Jupiter is truly giant, having actually a mass the is 318 times the of the Earth, and virtually 1/1000th that of the Sun! that is 11 time Earth’s diameter and also 1/10th the of the Sun. Jupiter’s density is around 1.3 gm/cm3, much reduced than any type of of the terrestrial planets, and Saturn while 95 time the Earth’s mass, has actually only a thickness of 0.7 gm/cm3, the shortest of any kind of planet. It would float in water.

Uranus and Neptune are considerably smaller, gift only around 5% the massive of Jupiter. Thus these planets space intermediate in between the terrestrial and also Jovian planets. Their densities room 1.2 gm/cm3 and 1.6 gm/cm3, respectively. Keep in mind that despite their smaller mass and lesser interior compression, this densities are greater than Saturn’s. Thus, your composition need to be basically different, with significant amounts of products heavier than the hydrogen and helium that write Jupiter and also Saturn.

Appearance and also Rotation

When observing the gigantic planets we see just the outer atmospheres, composed mainly of gaseous hydrogen and also helium. The uppermost cloud decks the Jupiter and Saturn space composed greatly of ammonia crystals. On Neptune the upper cloud deck is methane, when Uranus has actually no obvious cloud deck at every (only a deep, featureless haze).


Jupiter is plainly a colorful and also dynamic planet. Details in the cloud patterns enable a determination of the rotation price of the upper atmosphere. However, this may have small to execute with the turn of the underlying world (mantle and also core), which is finest found by observing the regular variations the the magnetic field. This rotation duration is 9h56m – the shortest “day” in the solar system.

Saturn’s rotation period (10h40m) is figured out from sport in that is radio emissions, i m sorry are connected to the magnetic field. Rotation of the planetary magnetic areas fixes Uranus’s rotation duration at 17h14m, and Neptune’s in ~ 16h6m.

Jupiter’s rotation axis is tilted at just 3o, so there are no seasons to speak of. Saturn and also Neptune are considerably tilted (at 27o and 29o), and so experience comparable seasons. Uranus has actually an axis tilted by 98o loved one to (solar system) north. This results in very strange seasons, with each pole alternately dealing with the sunlight for 40 years at a time.

Composition and also Structure

Jupiter and Saturn virtually certainly have interiors written of hydrogen and also helium. While these gases have actually only in reality been measured in the atmospheres of these planets, calculations done 50 years earlier by Yale astronomer Rupert Wildt display that these room the just two products which could an outcome in planets through the masses and densities the Jupiter and also Saturn. There room some uncertainties linked with absence of knowledge of the compressibilities of fluid hydrogen and also helium in ~ the temperatures and also pressures found within this planets. Pressure are estimated to be around 1 million bar and also densities around 31 gm/cm3.

Internal frameworks of the giant planets are very different from the terrestrial planets. Together one moves towards the center of Jupiter or Saturn the pressures become so high that hydrogen exists very first in a liquid kind and climate a liquid metallic form. In the case of Uranus and Neptune, the pressures most likely do no reach sufficient levels to liquefy hydrogen.


The cores of each of these planets space composed of more heavier materials. This is known from analysis of gravitational fields. These room most likely the rock/ice body which formed prior to the catch of big amounts of gases indigenous the early on solar nebula. However, the “rock and ice” many likely has a an extremely unfamiliar type at the pressures (tens of countless bar) and also high temperature which exist in ~ the cores that the planets.

For Jupiter and also Saturn the cores make up only a tiny portion of the complete planet mass, but most the the fixed of Uranus and Neptune is this core mass. Thus the last 2 planets were unable come attract big quantities that hydrogen and also helium.

Note the Jupiter has nearly the maximum mass for an item composed that “cold” hydrogen. This method that it is not generating power in the way that a star does. Less enormous objects than Jupiter would occupy a smaller volume, and more massive body would likewise be compressed by the higher gravity come a smaller sized volume. These an ext massive thing which are unable to ignite together stars room brown dwarfs or infrared dwarfs.

Internal heat Sources

Due to their big sizes, every of the huge planets to be heated considerably during development by the fallen of the nebular product onto the world core. Being the largest, Jupiter to be heated the most. Additionally, big gaseous planets can generate warm after formation by sluggish contraction. A shrinkage that a few millimeters every year can generate far-reaching energy.

Nevertheless, the exploration in 1969 by candid Low the Jupiter had an interior energy source was fairly surprising. Low offered a little 12-inch telescope carried over the mass of the atmosphere’s water vapor in a NASA Lear jet. After ~ a similar internal source for Saturn to be detected, philosophers calculated that such effects were, in fact, expected.

Jupiter’s price of internal energy generation is 4 X 1017 watts. This is around the same as the rate at i beg your pardon Jupiter absorbs power from the Sun. For this reason Jupiter’s setting is kind of intermediate between a regular planetary environment which obtains most of its power from the Sun, and a star’s atmosphere which is completely heated native below. The mass of this internal energy of Jupiter is primordial.

Saturn’s internal energy resource is about half of Jupiter’s. Due to the fact that Saturn has only a quarter the mass of Jupiter, this implies a better rate the internal energy generation. Through its lower mass Saturn should also have much less primordial heat left over from that formation. The source is thought to be as result of the separation the helium native hydrogen in the interior. In the fluid hydrogen mantle, heavier helium drops kind which then sink toward the main point of the planet, release gravitational energy. The is, Saturn is tho in the process of differentiating! This process occurs in Saturn and also not Jupiter because of the cooler temperatures within Saturn. In Jupiter the higher temperature keeps the hydrogen and also helium well-mixed.

Neptune has a little internal warmth source, if Uranus has actually no measurable interior source. For this reason these 2 planets have about the same efficient temperatures despite their different distances from the sun. What reasons this difference between the 2 otherwise very comparable planets is unknown.

Atmospheres that the Jovian Planets

Atmospheric Composition
CH42 X 10-32 X 10-3
NH32 X 10-42 X 10-5
C2H28 X 10-71 X 10-7
C2H64 X 10-58 X 10-6
PH34 X 10-73 X 10-6

While spectroscopy was applied to the Jovian planets beginning in the late 1800s, the spectra obtained could not be interpreted for part time. At first these planets to be suspected of gift self-luminous, so the their spectra consisted of emission bands. Right into the 1930s many of te primary absorption bands in the spectra remained unidentified. At this suggest CH4 and NH3 were determined in the environments of Jupiter and also Saturn.

Initially thought to be primary contents of the atmospheres, these 2 compounds space now well-known to be overcame by hydrogen and helium. The spectral signatures of hydrogen and also helium are an overwhelming to detect, and only ~ the Voyager encounters can the quantity of helium be reliably determined.

The compositions ( of the atmospheres of Jupiter and Saturn room similar, except that Saturn has less helium in its environment as a result of helium having condensed and resolved toward the center of Saturn, therefore generating (at the very least a part of) Saturn’s interior energy.

The settings of Uranus and also Neptune have around the same family member abundances of hydrogen and also helium as Jupiter.

Clouds and also Structure the Atmospheres



The clouds on Jupiter are constantly changing, and variety in shade from white to orange to red and brown. Saturn’s cloud task is similar, but reasonably subdued.

At the temperatures and pressures uncovered in the upper environments of Jupiter and Saturn methane stays a gas, however ammonia is able come condense simply as water vapor go in Earth’s atmosphere. This frozen condensed ammonia produce clouds – the clouds we see once we watch at these planets. The ammonia cloud deck clues the top edge that the convective troposphere, through the cold stratosphere over it.

On Jupiter and also Saturn the temperature close to the cloud tops is around 140 K. In Jupiter’s instance the press at this level is about 0.1 bar, if on Saturn the push at the cloud tops is 1 bar. Because the ammonia clouds lie so lot deeper ~ above Saturn, they space more challenging to see, causing a more uniform appearance.

In the tropospheres of these planets the temperature and pressure both boost with depth within the atmosphere. The Galileo probe has listed the most thorough look at Jupiter’s atmospheric structure.

For the Galileo residence page see:

Above the ammonia clouds the Jupiter the setting is clear and cold, with a minimum temperature of around 120 K. At greater altitudes the temperature rises again, as it walk in the Earth’s atmosphere, because of the absorb of UV radiation. Photochemical reactions produce a selection of fairly complicated hydrocarbons. Thus a thin photochemical smog overlies the visible clouds.

The coloration of the clouds must be due to the existence of some various other chemical(s), because the ammonia clouds would certainly be white. This other products may be hydrocarbons, or possibly sulfur or phosphorus.

The framework of Saturn’s setting is similar, back the temperature are somewhat lower and also the environment is much more extended as result of the lower gravity, yet otherwise the two are qualitatively similar.


The setting of Uranus is featureless as seen from the infrared v ultraviolet variety of wavelengths. Theoretically, Uranus’ environment should resemble that of Saturn and also Jupiter, other than that the upper condensation cloud class is written of CH4 rather than NH3. Also, the lack of an internal heat source causes there to be small convection and a stable environment with little visible structure. The troposphere is concealed from see by a very deep and cold stratosphere.

Although the atmospheric structure and effective planetary temperature are virtually the exact same for Uranus and Neptune, Neptune’s figure is different. The top clouds space composed that methane, developing a slim cloud layer near the height of the troposphere wherein the temperature is 70 K and the pressure 1.5 bar. Over this level the the atmosphere is clean without the haze uncovered on Uranus. Over there is a 2nd cloud layer listed below at a pressure of about 3 bars, more than likely composed of hydrogen sulfide ice cream crystals. The cause of this difference between Uranus and also Neptune is the existence of much more active convection top top Neptune because of its internal heat source. The convection currents bring warmed gases above the 1.5 bar cloud deck, forming added clouds around 75 km higher.


Winds and also Weather

By observing cloud patterns it is feasible to measure up wind speeds and also track the circulation that the atmosphere. The it was observed dynamics space fundamentally different from those observed in the terrestrial planet atmospheres. These differences result from (1) much deeper atmospheres with no solid lower boundary, (2) faster rotation rates which suppress N-S circulation patterns and also accentuate E-W patterns, and also (3) v the exception of Uranus, internal heat sources contribute about as much energy to the environment as sunlight does, forcing deep convection.

On Jupiter, the main feature of the visible cloud great is the alternation that light and also dark bands parallel come the equator and stretching roughly the planet. Back the intensity and also position move slightly native year to year, these space semi-permanent features.

Although much less obvious, the underlying E-W wind trends are an ext fundamental, and do not appear to change, also over long periods the time. There is an equatorial eastward jet stream of around 100 m/s (300 km/hr), with alternative eastward and also westward relocating streams at greater latitudes. The north and also south hemispheres are an extremely nearly mirror photos of every other. Saturn’s zonal winds present a comparable pattern, yet with a much higher equatorial circulation rate the 400 m/s (1300 km/hr).


The lighter fancy zones room upwelling convection currents topped through white ammonia clouds. The darker belts space downflowing convection regions, v darker shade due come the relative absence of ammonia clouds. The is also possible that the capability to view deeper into the atmosphere reveals the lower lying ammonium hydrosulfide clouds.

In spite of Uranus’ strange periods (due to its 98o axial tilt), its simple circulation pattern is eastern to west. The extent of the atmosphere and its capacity to retain warm are so huge that the alternative 40-year sunlight/darkness bicycle has tiny effect.

Neptune’s “weather” is identified by solid east-west winds which are generally similar to Jupiter’s and also Saturn’s. Equatorial wind speeds space 600 m/s (2100 km/hr), nearly supersonic.


In addition to the regular atmospheric circulation, there space localized disturbances – storms, to usage a terrestrial terminology. The most prominent instance being the huge oval high push regions on both Jupiter and Neptune. Because that example, the “Great Red Spot” (GRS), almost 30,000 km in length, was very first seen 300 year ago. This “storm” is plainly much longer-lived than terrestrial storms. It additionally differs in the it is a high pressure an ar with a six-day anticyclonic rotation. Three smaller sized “white ovals,” about 10,000 km in size formed around 1940. Back the reason of these storms is unknown, their longevity can be understood. On planet a hurricane or typhoon has actually a lifetime of a few weeks, or less when friction v land occurs. On Jupiter over there is no solid surface to slow-moving the disturbance, and also the shear dimension of the disturbance makes it satble. Calculations show that for functions as large as the GRS the lifetime is measured in centuries, if the white ovals have actually lifetimes of decades.

Although smaller sized in size and with various cloud composition, Neptune has actually an atmospheric feature really like the GRS. Neptune’s “Great Dark Spot” is practically 10,000 km long. It is discovered (like the GRS) at 20o S latitude, and its size and shape are proportionally the similar to the GRS. This an excellent Dark clues is additionally anticyclonic through a duration of 17 days.


All the Jovians have solid magnetic fields.

Jupiter’s is strongest, 20 to 30 x the of earth.

Source Dynamo effect: Jupiter has actually (1) liquid interior–metallic H (2) Electrically Conducting internal –the metallic H (3) fast rotation.

Tilted around 15 degrees to planet’s rotation axis. And also offset native the center of planet by about 18000 km.

Strong radio radiation called synchrotron radiation emitted by fee particles (electrons, ions) trapped in the magnetosphere, whirling approximately the magnetic field lines.

Saturn has strong field, aligned with rotation axis.

Uranus has strong field, comparable to Saturn and tipped 60 levels to rotation axis, a vast amount! favor Jupiter’s it’s offset from center of planet.

Neptune’s field is likewise tilted around 55 degrees and offset nearly half the planet’s radius from the center.

Could seemingly arbitrarily alignments of fields suggest to changes in planets interior rotation? proof of primordial collisions, perhaps? Still extremely speculative.

Planetary Magnetic Fields

Magnetosphere that JupiterIo Plasma TorusMagnetospheres the Saturn, Uranus, Neptune

Pluto and Charon

Pluto page

Orbit and also Characteristics the Pluto

Pluto is neither a terrestrial planet, no one a Jovian. In ~ 2300 km diameter, that is really small, and also probably just one of countless such objects that when orbited the Sun beyond the gas huge planets. Many astronomers think that Pluto need to be classified together a minor planet or asteroid.

Pluto’s orbit is very inclined (highest of any kind of planet) to the ecliptic (17o), and also its eccentricity is also ther highest possible in the solar mechanism at 0.248. Its mean distance from the sun is 5.9 exchange rate km, however its perihelion distance is just 4.5 billion kilometres – in reality inside the orbit that Neptune. Having actually passed perihelion in 1989, it continues to be inside Neptune’s orbit till 1999. The orbital period is 248.6 years.

Discovery that Charon

In 1978 James Christy (USNO) uncovered Pluto’s only recognized satellite, Charon. He listed that photos of Pluto taken v the 1.5 m telescope to be elongated, but those the stars in the same picture were not. Research proved that part other pictures taken that Pluto proved the same phenomenon, yet most go not.

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Rings and also Satellite Systems

Satellites the the Jovian Planets

Note: We’ll shot to discuss representative instances from the plenty of satellites of the Jovian planets, and shot to draw some all at once conclusions about their satellite systems.