Lesson Objectives

Describe crucial features the the outer planets and their moons.Compare the outer planets to each other and also to Earth.

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Galilean moonsgas giantsGreat Red Spotouter planetsplanetary rings


The 4 outer planets space farther from the Sun and also farther native Earth. They are lot more an overwhelming to learn around since they are really different native our residence planet.

The external Planets

The 4 planets the furthest from the Sun room the outer planetsFigure below shows the family member sizes the the outer planets and the Sun. This planets room much larger than the inside planets and also are made mainly of gases and liquids, so they are also called gas giants.


This image shows the four outer planets and also the Sun, with sizes to scale. Native left come right, the external planets are Jupiter, Saturn, Uranus, and Neptune.

The gas giants are made up primarily of hydrogen and helium, the same elements that make up most that the Sun. Astronomers think that hydrogen and also helium gases comprised much that the solar system when it first formed. Due to the fact that the inner planets didn’t have sufficient mass to organize on to these light gases, your hydrogen and also helium floated away right into space. The Sun and also the massive outer planets had sufficient gravity to store hydrogen and also helium from drifting away.

All that the external planets have many moons. Castle all additionally have planetary rings, created of dust and also other tiny particles the encircle the world in a slim plane.


Because Jupiter is for this reason large, it mirrors a the majority of sunlight. Jupiter is incredibly bright in the night sky; only the Moon and also Venus space brighter (Figure below). This brightness is every the more impressive because Jupiter is quite far from the earth — 5.20 AUs away. That takes Jupiter around 12 planet years come orbit once roughly the Sun.


This image of Jupiter was taken through Voyager 2 in 1979. The colors to be later amplified to lug out much more details.

Jupiter is named for the king the the god in roman inn mythology. The earth is enormous, the largest object in the solar mechanism besides the Sun. Back Jupiter is over 1,300 time Earth’s volume, it has only 318 times the fixed of Earth. Favor the various other gas giants, that is much less dense than Earth.

Check the end NASA’s world book to learn more about Jupiter: http://www.nasa.gov/worldbook/jupiter_worldbook.html.

A ball of Gas and also Liquid

Astronauts trying to land a spaceship ~ above the surface of Jupiter would discover that over there is no solid surface ar at all! Jupiter is made mainly of hydrogen, through some helium, and small amounts of other elements (Figure below).


Jupiter’s setting is composed of hydrogen and helium. Deeper in ~ the planet, push compresses the gases into a liquid. Some evidence suggests that Jupiter may have a tiny rocky core of heavier elements at that is center.

A Stormy Atmosphere

The top layer that Jupiter’s atmosphere includes clouds that ammonia (NH3) in bands of various colors. These bands rotate around the planet, but also swirl about in turbulent storms. The Great Red Spot (Figure below) is an enormous, oval-shaped storm discovered south that Jupiter’s equator. This storm is more than 3 times as vast as the entire Earth. Clouds in the storm rotate in a counterclockwise direction, do one finish turn every six days or so. The good Red Spot has been on Jupiter because that at least 300 years, because astronomers could first see the storm v telescopes. Execute you think the great Red clues is a permanent function on Jupiter? How could you know?


This image of Jupiter’s good Red clues (upper ideal of image) to be taken by the Voyager 1 spacecraft. The white storm just below the great Red spot is around the very same diameter together Earth.

Jupiter’s Moons and Rings

Jupiter has a very huge number that moons — 63 have actually been uncovered so far. Four are large enough and also bright enough to be viewed from Earth, utilizing no more than a pair the binoculars. These moons — Io, Europa, Ganymede, and also Callisto — were an initial discovered by Galileo in 1610, therefore they are sometimes referred to together the Galilean moons (Figure below). The Galilean moons are bigger than the dwarf planets Pluto, Ceres, and Eris. Ganymede is not just the biggest moon in the solar system it is even larger than the earth Mercury!


This composite photo shows the 4 Galilean moons and also their sizes loved one to the great Red Spot. From height to bottom, the moons are Io, Europa, Ganymede, and also Callisto. Jupiter’s good Red clues is in the background. Sizes space to scale.

Scientists are specifically interested in Europa due to the fact that it may be a ar to find extraterrestrial life. What features could make a satellite so far from the sunlight a candidate because that life? return the surface of Europa is a smooth great of ice, there is evidence that there is an ocean of liquid water under (Figure below). Europa additionally has a continual resource of power — that is heated as it is stretched and also squashed through tidal forces from Jupiter. Numerous missions have been plan to explore Europa, consisting of plans come drill v the ice and send a probe right into the ocean. However, no together mission has actually yet to be attempted.


An intensified color image of a part of Europa’s icy surface. The surface ar ice may have actually motions similar to plate tectonics on Earth.

In 1979, 2 spacecrafts — Voyager 1 and Voyager 2 — saw Jupiter and also its moons. Photos from the Voyager goals showed the Jupiter has actually a ring system. This ring device is an extremely faint, so that is difficult to observe from Earth.


Saturn, displayed in Figure below, is famous for that beautiful rings. Although every the gas giants have rings, only Saturn’s can be quickly seen from Earth. In roman inn mythology, Saturn to be the dad of Jupiter.

Saturn’s massive is around 95 times the fixed of Earth, and also its volume is 755 times Earth’s volume, making that the 2nd largest world in the solar system. Saturn is additionally the least dense planet in the solar system. It is less thick than water. What would happen if you had a big enough bathtub to put Saturn in? Saturn would certainly float! Saturn orbits the sun once around every 30 earth years.


This picture of Saturn and also its ring is a composite of pictures taken by the Cassini orbiter in 2008

Like Jupiter, Saturn is made greatly of hydrogen and also helium gases in the outer layers and liquids at higher depths. The upper environment has clouds in bands of different colors. These revolve rapidly around the planet, but there appears to be less turbulence and also fewer storms ~ above Saturn than on Jupiter. One exciting phenomena that has been it was observed in the storms top top Saturn is the existence of thunder and also lightning (see video, below). The planet likely has a small rocky and metallic core.

Cassini scientists waited years because that the right conditions to create the an initial movie that shows lightning on one more planet — Saturn.http://saturn.jpl.nasa.gov/video/videodetails/?videoID=210 Lots an ext videos from the Cassini mission room indexed here:http://saturn.jpl.nasa.gov/video/

Saturn’s Rings

In 1610 Galileo an initial observed Saturn’s rings through his telescope, however he thought they can be two big moons, one ~ above either side of the planet. In 1659, the dutch astronomer Christian Huygens realized the the features were rings (Figure below).

Saturn’s ring circle the planet’s equator and appear tilted due to the fact that Saturn itself is tilted around 27 degrees. The rings perform not touch the planet.


A color-exaggerated mosaic the Saturn and also its ring taken by Cassini as Saturn eclipses the Sun.

The Voyager 1 and also 2 spacecraft in 1980 and also 1981 sent ago detailed images of Saturn, the rings, and also some that its moons. Saturn’s rings room made of corpuscle of water and also ice, with some dust and rocks (Figure below). There are several gaps in the rings that scientists think have originated because (1) the material was cleared the end by the gravitational traction within the ring or (2) by the gravitational pressures of Saturn and of moons external the rings.


A close-up the Saturn’s external C ring showing locations with greater particle concentration and gaps.

The rings to be likely developed by the breakup of one of Saturn’s moons or from product that never ever accreted right into the planet as soon as Saturn originally formed.

An computer animation of dark spokes in Saturn’s rings is watched here:http://en.wikipedia.org/wiki/File:Saturn_ring_spokes_PIA11144_300px_secs15.5to23_20080926.ogv. The spokes show up seasonally and also their origin is as yet unknown.

Saturn’s Moons

Most of Saturn’s moons space very tiny and just seven are big enough for gravity to have actually made castle spherical. Just Titan is bigger than earth’s Moon at around 1.5 time its size. Titan is even larger than the earth Mercury.

Scientists space interested in Titan since its setting is comparable to what Earth’s was like prior to life developed. Nitrogen is dominant and methane is the second most numerous gas. Titan may have a layer of fluid water and also ammonia under a layer of surface ice. Lakes of liquid methane (CH4) and also ethane (C2H6) are found on Titan’s surface. Although conditions are comparable enough come those of at an early stage Earth for scientists to speculate that incredibly primitive life may exist top top Titan, the too much cold and lack that carbon dioxide do it i can not qualify (Figure below).


This composite picture compares Saturn’s largest moon, Titan (right) to planet (left).


Uranus (YOOR-uh-nuhs) is called for the Greek god of the skies (Figure below). From Earth, Uranus is for this reason faint the it to be unnoticed by ancient observers. Wilhelm Herschel first discovered the planet in 1781.


Uranus is an icy blue-green ball.

Although Uranus is very large, the is very far away, about 2.8 billion km (1.8 exchange rate mi) from the Sun. Light from the sun takes about 2 hours and 40 minutes to reach Uranus. Uranus orbits the sunlight once about every 84 planet years.

Uranus has a mass around 14 times the massive of Earth, yet it is lot less thick than Earth. Heaviness at the surface ar of Uranus is weaker 보다 on Earth’s surface ar so if you were at the peak of the clouds on Uranus, you would certainly weigh around 10% less than what you weigh on Earth.

An Icy Blue-Green Ball

Like Jupiter and Saturn, Uranus is composed largely of hydrogen and also helium, through an outer gas layer the gives way to liquid on the inside. Uranus has actually a greater percentage that icy materials, such together water, ammonia (NH3), and also methane (CH4), than Jupiter and Saturn.

When sunlight reflects off Uranus, clouds the methane filter out red light, offering the planet a blue-green color. There are bands that clouds in the setting of Uranus, however they are difficult to view in common light, so the world looks favor a plain blue ball.

The sideways Planet

Most the the planets in the solar mechanism rotate on your axes in the same direction the they move roughly the Sun. Uranus, though, is tilted ~ above its next so that is axis is practically parallel come its orbit. In various other words, the rotates favor a top that to be turned so the it to be spinning parallel to the floor. Researchers think that Uranus was most likely knocked over by a collision with one more planet-sized object billions of years ago.

Rings and Moons the Uranus

Uranus has a faint system of ring (Figure below). The rings circle the planet’s equator, but since Uranus is tilted on its side, the rings are practically perpendicular to the planet’s orbit.


This photo from the Hubble room Telescope reflects the pass out rings that Uranus. The world is tilted on its side, therefore the ring are practically vertical.

Uranus has actually 27 well-known moons and also all but a couple of of lock are called for characters from the plays of william Shakespeare. The five biggest moons of Uranus — Miranda, Ariel, Umbriel, Titania, and also Oberon — are presented in Figure below.


These Voyager 2 photos have been resized to display the relative sizes that the 5 main moons the Uranus.


Neptune, displayed in Figure below, is the only significant planet the can’t be seen from planet without a telescope. Researchers predicted the presence of Neptune before it was discovered due to the fact that Uranus go not constantly appear specifically where it need to appear. Lock knew that the gravitational traction of one more planet past Uranus need to be influence Uranus’ orbit.

Neptune was discovered in 1846, in the place that had been predicted, and also it was named Neptune for the roman god the the sea since of its bluish color.


This photo of Neptune was taken by Voyager 2 in 1989. The good Dark Spot checked out on the left center in the snapshot has because disappeared, however a similar dark clues has showed up on another component of the planet.

In many respects, Neptune is similar to Uranus (Figure below). Neptune has slightly much more mass than Uranus, however it is slightly smaller in size. Neptune is much farther indigenous the sun at nearly 4.5 billion kilometres (2.8 billion mi). The planet’s slow orbit way that the takes 165 earth years to walk once roughly the Sun.


Neptune’s composition is the of a gas giant: (1) upper atmosphere, (2) environment composed the hydrogen, helium and also methane gas, (3) mantle the water, ammonia and methane ice, (4) core of rock and ice.

Extremes of Cold and also Wind

Neptune’s blue color is mostly because of frozen methane (CH4). Once Voyager 2 visited Neptune in 1986, there to be a huge dark-blue spot that scientists named the good Dark Spot, south of the equator. Once the Hubble space Telescope took pictures of Neptune in 1994, the great Dark Spot had disappeared but another dark clues had showed up north that the equator. Astronomers think the both of these spots stand for gaps in the methane clouds top top Neptune.

The changing appearance the Neptune is brought about by its turbulent atmosphere. The winds top top Neptune room stronger 보다 on any type of other planet in the solar system, reaching speeds the 1,100 km/h (700 mi/h), close to the speed of sound. This excessive weather surprised astronomers, due to the fact that the earth receives tiny energy native the sun to power weather systems. Neptune is likewise one that the coldest locations in the solar system. Temperatures at the optimal of the clouds are about -218oC (-360oF).

Neptune’s Rings and Moons

Neptune has faint ring of ice and dust that may readjust or disappear in relatively short time frames.

Neptune has 13 recognized moons. Triton, displayed in Figure below, is the only among them the has enough mass to it is in spherical in shape. Triton orbits in the direction opposite to the orbit that Neptune. Researchers think Triton did not kind around Neptune, but instead was captured by Neptune’s gravity as it pass by.


This image Triton, Neptune’s largest moon, was taken through Voyager 2 in 1989.

Fly by Neptune’s moon Triton by city hall this video: http://www.space.com/common/media/video/player.php?videoRef=mm32_SunDeath#playerTop

Lesson Summary

The 4 outer planets are all gas giants made mostly of hydrogen and helium. They have actually thick gaseous outer layers and also liquid interiors.The external planets have numerous moons, and planetary rings.Jupiter, by far the largest planet in the solar system, has actually bands of different colored clouds, and also a long-lasting storm called the an excellent Red Spot.Jupiter has an ext than 60 moons including the 4 largest, the Galilean moons.Europa has an s of fluid water under a great of ice whereby life may have actually formed.Saturn is smaller sized than Jupiter yet has a huge system of beautiful rings.Titan’s setting is comparable to beforehand Earth’s and also the moon might harbor primitive life.Uranus and Neptune were discovered reasonably recently due to the fact that they are so much away.Uranus is tilted top top its side, probably due to the fact that of a previous collision v a huge object.Neptune is very cold and also has strong winds. The dark spots are storms in Neptune’s atmosphere.

Review Questions

1. Surname the external planets a) in order from the sun outward, b) from largest to the smallest by mass, and also c) from largest to the smallest by size.

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2. Why space the outer planets referred to as gas giants?

3. Just how do the good Red spot and great Dark point out differ?

4. Surname the Galilean moons, and explain why they have actually that name.

5. Why can Europa it is in a likely place to find extraterrestrial life?

6. What reasons gaps in Saturn’s rings?

7. Why are scientists interested in the atmosphere of Saturn’s moon Titan?

8. What liquid is uncovered on the surface ar of Titan?

9. Why is Uranus blue-green in color?

10. What is the surname of Neptune’s largest moon?

Further reading / Supplemental Links

Points come Consider

The inside planets are little and rocky, when the outer planets are large and gaseous. Why could the planets have created into these 2 groups?We have discussed the Sun, the planets, and also the moons that the planets. What other objects deserve to you think that that deserve to be found in ours solar system?