The Outer Planets are Jupiter, Saturn, Uranus, and Neptune. Think for a moment about these Outer Planets. They are very different from the Inner Planets….no doubt due to a large extent on the amount of heat that these two groups of planets receive from the sun. The Outer Planets retained their gas atmospheres due to the much cooler temperatures. But there are other differences that have not been totally explained. It is odd that some of the outer Planets have a rocky core similar to the Inner Planets, and some consist of only gas and liquids. Why would some planets consist only of gases? And furthermore, why do these gas planets have rocky moons? How did this clear separation of material occur? We may have to wait for these answers but it is interesting to know that all is not as simple as it seems. Below you will find basic information on each planet, note the differences with Earth and imagine what daily events may be occurring on each planet.
The following Table indicates the spacecraft that have been sent to the planets, the most recent is at the top of the list.
| Jupiter | Saturn | Uranus | Neptune |
| New HorizonsCassini
Ulysses Galileo Voyager 2 Voyager 1 Pioneer 11 Pioneer 10 |
Cassini-HuygensVoyager 2
Voyager 1 Pioneer |
Voyager 2 | Voyager 2 |
Color represents the Satellite ownership, as follows:
| USA (NASA) | European Space Agency | China | India | Japan | Russia |
Jupiter
Description
Gas giant. The largest planet in our solar system, at 317 times the mass of Earth. The visible clouds are mostly ammonia. The atmosphere is mostly hydrogen and helium and extends down to a point where the pressure forms liquid hydrogen. At a depth about two-third’s of the radius, the liquid hydrogen becomes metallic due to the high atmospheric pressure. At the center there is thought to be a rock-ice core about the size of earth.
Jupiter has 49 officially named Moons and many more identified with a number only. The four largest moons are planet sized and were discovered by Galileo with his small primitive telescope. These moons are shown in the photo above, top to bottom:
| Io – most volcanically active body in the solar system with an atmosphere of sulfur dioxide. No water present. Third largest of Jupiter’s satellites. 262,000 miles from Jupiter. | |
| Europa – size of our moon, covered with an ocean of salty water with it’s surface frozen. It has an atmosphere of oxygen. It could support simple life forms. 420,000 miles from Jupiter. Imagine for a moment that you are on the surface of Europa, the moon is on the sunny side of Jupiter and you are on the sunny side (facing the sun).. There is not a lot of light since the sun is 5 times as far away as it would be on Earth. Nevertheless Europa rotates around and the sun sets. You might expect it would get dark, but lo and behold….it starts to get brighter. As you rotate around and begin to face Jupiter you discover that Jupiter fills the “night” sky. It is huge…. stretching from horizon to horizon! And the reflected light from Jupiter turns the sunless sky even brighter still! | |
| Ganymede – The largest moon in the solar System. It may have a liquid water ocean beneath it’s crust of water ice and rocks. It may also have a thin oxygen atmosphere. 625,000 miles from Jupiter. | |
| Callisto – Many Impact craters. No volcanoes and no geologic activity. It is a dead planet, thought to have the oldest landscape in the solar system….4 million years old.. Second largest of Jupiter’s satellites. 1,170,000 miles from Jupiter. |
Just as an explorer on Europa would experience a very bright night time when Europa was between the Sun and Jupiter, so it would be with all of Jupiter’s moons….Jupiter would fill the night sky and reflect more light than the daytime! Truly, the day would be darker than night!
Weather
It’s very interesting to think of how to describe the weather on Jupiter. If you were standing on the rocky core, you’d be encased in metallic hydrogen….I suppose that would qualify for no weather at all! If on the other hand you were above the metallic hydrogen and the liquid hydrogen, it would be windy, rainy (liquid hydrogen), and very cold. If you were higher in the ammonia clouds you would experience very high winds. It would be cold. The good news is there would be no dust and no dirt!
Viewing
Jupiter can be easily seen with the naked eye. The moons of Jupiter can be seen with a small telescope.
Visitors
(Names in Bold are still operational, strikethrough were not successful, blue are future.)
- Europa Astrobiology Lander. Proposed for 2036 to land on the moon Europa.
- Juno. In development for 2016. This space craft will study the gravity field, magnetic field and atmosphere of Jupiter.
- Prometheus One. Proposed for 2015. To orbit three of Jupiter’s moons.
- New Horizons – February 27, 2007. Single fly-by. Photos of Callisto.
- Cassini-Huygens – 2000. Single fly-by. Continued on to orbit Saturn.
- Ulysses – February 8, 1992. ESA. Made 3 passes (Flybys) studying the atmosphere and fields of Jupiter. Continued on to orbit the Sun.
- Galileo – December 7, 1995. Mapping and atmospheric measurements. Released a probe to study the atmosphere, which lasted 58 minutes as it was consumed by the high pressures, intense radiation, and high winds. At the end of its mission in 2003, the space craft was intentionally crashed into Jupiter.
- Voyager 2 – July 9, 1979. Images of Io, Europe, and Ganymede. Headed for Interstellar space via Saturn.
- Voyager 1 – March 5, 1979. Single fly-by. Headed for Interstellar space via Saturn.
- Pioneer 11 – December 2, 1974. Single fly-by to take photos, atmospheric measurements. Contact lost in 1995.
- Pioneer 10 – December 3, 1973. Single fly-by to take photos and magnetosphere measurements. Continues the mission to exit the solar system.
Saturn
Description
Gas giant. Atmosphere is 97% Hydrogen and 3% helium
Saturn has 52 moons with Titan being the largest. Titan’s atmosphere is dominated by Nitrogen, similar to Earth, Earth is 78% N2 while Titan is 95% N2. Although much smaller than Earth, Titan’s atmospheric pressure is about 50% greater than Earth. The temperature is around -290oF. Frozen water forms the land and liquid ethane and methane form the lakes, rivers, and rain……a strange land indeed.
Weather
Saturn
Viewing
Visitors
(Names in Bold are still operational, strikethrough were not successful, blue are future.)
- Future Flybys to be launched in 2015 will include several probes to be released into the planets atmosphere.
- Cassini-Huygens. Inserted into Saturn orbit on July 1, 2004. The Huygens probe was released on December 24, 2004 in the vicinity of the moon Titan and landed on Titan 2 weeks later on January 14, 2005. The spacecrafts orbit brings it in close proximity to the moons of Saturn where it is able to make measurements of the atmosphere and surface of the moons.
- Voyager 2. August 26, 1981 Flyby with the closest approach to Saturn at 62,000 miles above Saturn. It took photos of Saturn and several of its moons before departing to Uranus. It currently is traveling toward interstellar space and is continues to be operational.
- Voyager 1. November 11, 1980 Flyby with the closest approach to Saturn at 77,000 miles. Voyager 1 took hi-resolution photos of Saturn and its Moon Titan. It currently is traveling toward interstellar space and is continues to be operational.
- Pioneer 11. First spacecraft to visit Saturn. September 1, 1979 Flyby. Pioneer 11 took photos of Saturn and then continued on to eventually leave the solar System. All contact with the spacecraft was lost in November 1995, however the craft continues to travel towards interstellar space.
Uranus
Description
Uranus is very odd planet in that it spins on it’s side relative to its orbit around the Sun. It is a true Gas giant in that there is no solid rocky core, however it does have a condensed liquid core made up of water, ammonia, and methane. The atmosphere consists of hydrogen and helium, as well as methane and traces of water and ammonia. It’s blue-green color comes from the methane in the atmosphere.
Uranus has 27 known moons and 11 rings.
Weather
Cold and dark. The surface is covered with liquid so you will need a flotation device
Viewing
Visitors
(Names in Bold are still operational, strikethrough were not successful.)
- Voyager 2. January 24, 1986. Single Flyby to study atmosphere and the magnetic field.
Neptune
Description
Named after the Roman God of the Sea. Atmosphere of hydrogen and methane. Neptune also has rings consisting of small rocks and ice. It is thought that Neptune has an earth-sized rocky core covered with water and other melted ices from the atmosphere. The deep blue color is due to methane and another element which currently remains a mystery.
Neptune has 13 moons including Triton, the largest of Neptune’s moons and one of just a few moons in the Solar System which has active geysers.
Weather
Cold and dark. Sustained winds can be several hundred miles per hour. If you are on the surface of the rocky core you will need a boat as the surface is covered with liquid water, hydrogen, and methane
Viewing
Too small to see with the unaided eye.
Visitors
Only 1 visitor to Neptune…
- Voyager 2 – August 24, 1989. Single fly-by. Measured physical characteristics of Neptune and its moon Triton. Continued on to interstellar space.
No current or future missions in development.
Pluto
Description
Way too cold. Sorry, not a regular planet anymore. It is the first object to be classified as a Dwarf Planet, a new category. It is the smallest of the planets, having a diameter of just over 1400 miles….it would fit nicely in the Gluf of Mexico.
Pluto has 3 moons
| Charon (KARE-on) approximayely half the size of Pluto. | |
| Nix – very small. Little is known of this moon. | |
| Hydra – very small. Little is known of this moon. |
Weather
Cold, no wind, no rain, no clouds….basically no weather, however it does have a very thin atmosphere discovered in 1988.
Viewing
Impossible to see with the naked eye.
Visitors
| New Horizons. Currently enroute for arrival in 2016. Single Flyby of 150 days |