Jovian Planets

General Characteristics

• Thick atmosphere of hydrogen and helium (H and He)

• High mass (15 - 318 times mass of Earth)

• Large size, giant planets
  (3.8 - 11.2 times Earth's diameter)
  approx. 50,000 - 150,000 km diameter

• Low density
  0.7 - 1.8 g/cm3

• Year length (orbital period)
  • Jupiter 11.86 years
  • Saturn 29.46 years
  • Uranus 84.01 years
  • Neptune 164.8 years

• Day length (rotational period)
  • Jupiter 9.8 hours
  • Saturn 10.63 hours
  • Uranus 17.18 hours
  • Neptune 16.05 hours

• Axial inclination (degrees)
  • Jupiter 3.1
  • Saturn 26.7
  • Uranus 97.9 (on its side)
  • Neptune 29.6

• Many moons
  • Jupiter 16+
  • Saturn 17+
  • Uranus 15+
  • Neptune 8+

• Gravity is much stronger than on Earth.
  If you weighed 140 lb on Earth your weight on each of the Jovian planets is:
  • Jupiter 355 lb
  • Saturn 150 lb
  • Uranus 130 lb
  • Neptune 165 lb

• Low temperatures because of great distance from the sun
  -166 F to -319 F

Atmospheric composition

1. Jupiter
   • 83% H2
   • 17% He
   • H/He ratio = 9/1
   • Traces of methane (CH4), ammonia (NH3), water (H2O), and organic compounds such as ethane (C2H6) and hydrogen cyanide (HCN)

2. Saturn
   • H/He ratio = 14/1
   • Helium has probably sunk deep inside planet

3. Uranus
   • Atmosphere similar to Jupiter
   • H/He ratio = 7/1

4. Neptune
   • No helium yet detected spectroscopically
   • Assumed to have both H and He
   • Atmosphere contains abundant methane (CH4)
   • Also contains ethane and acetylene

With Jupiter, about one quarter of the way in, all of the hydrogen is liquid (molecular) hydrogen.

Deeper inside the planet, the gases are highly compressed, causing ionization.
The electrons are free to more, like in metals.
The material is electrically conductive.
Liquid metallic hydrogen.

Liquid metallic hydrogen may be the most abundant metal in the solar system, and yet there is none on Earth!

Internal Structure

The centers of the Jovian planets are probably rocky cores composed of heavier elements (such as O, Si, and metals) and water, methane, and ammonia. The cores of these planets are probably more massive than Earth, but may be roughly the same size (or not much larger).

Uranus and Neptune may have molten cores, because they are smaller, and have less pressure at their centers.
They are not massive enough to compress H into a liquid.
The interiors of Uranus and Neptune are probably hot, dense liquid water, methane, and ammonia.

The planets have internal heat sources.
Sources of heat?

1. Heat generated by meteoritic collisions, bombardment
2. Heat generated by great mass and compression
3. Heat generated by friction of sinking He atoms through H (Saturn)

More heat energy flows out of Jupiter and Saturn than they receive from the sun.

No heat source detected for Uranus (samller and less massive).

Neptune has a small amount of heat.

Temperatures in the planets' interiors may be tens of thousands of Kelvins.

Pressures in the interiors are tens of millions of times Earth's atmospheric pressure.

Rotational characteristics

Banding in the clouds

Magnetic Field

Rings