Jupiter and Saturn Jupiter and Saturn are the two largest and best known Jovian planets. Others include Uranus and Neptune. Pluto is considered as a separate object. Great Red Spot The four brightest moons are called the Galilean satellites after Galileo

While Jupiter is known for its four brightest moons and the red spot, Saturn is known for its extensive ring system.

Discovery of Uranus Uranus was discovered by William Herschel while cataloging stars. Uranus slowly moved among the stars proving it was a planet. Herschel wanted to name the planet “George” but was talked into Uranus by Johann Bode. a) Earth view b) Voyager 2 view

Discovery of Neptune The orbit of Uranus was being gravitationally perturbed by another unknown planet. After two years of searching, they found the planet within 2 degrees of its predicted position.

Physical Properties Notice for example that Jupiter is 315 times more massive than the Earth and 11 times bigger while being less dense. Since water has a density of 1000 kg/m3, Saturn would float in a bathtub.

It is difficult to measure the rotation rates of the Jovian planets because they have no “surface” to watch as they rotate. With nothing to tie them down different parts of the atmosphere rotate at different speeds (differential rotation). The Jovian planets are also known as the gas giants.

Jupiter’s Atmosphere Because of its high escape velocity, Jupiter has been able to retain all the lighter gasses including hydrogen and has the same chemical proportions as when it was created 4.6 billion years ago. It consists of 86% hydrogen, 14% helium, traces of methane, ammonia, and water vapor. After its four bright moons, Jupiter is best known for its cloud bans. The bands are the result of convection currents in the atmosphere. Lighter warmer gasses tend to ride on top (ammonia) and the cooler heavier gasses sink down (ammonium hydrosulfide) giving a light/dark pattern on the surface.

Weather on Jupiter In addition to the large scale band structures on Jupiter there are smaller structures. The most famous being the great red spot which is a hurricane storm which has been raging for over 300 years. Spacecraft have detected lightening and aurora.

Saturn’s Atmosphere Saturn is not as colorful or turbulent as Jupiter. This may be due to the fact that Saturn is cooler because it is further away from the Sun. It does not contain as large of storms not are they permanent. It also has enough gravity to hold on to all the gasses and consists of 92.4% hydrogen, 7.4 helium, and traces of methane and ammonium. The most famous thing about Saturn is its rings.

Color enhanced to show structure.

Some storms on Saturn actually encircle the planet. Sequence of images from Hubble

Atmospheres of Uranus and Neptune Both planets have similar makeup to Jupiter and Saturn Uranus: 84% hydrogen, 14% helium, 2% methane Neptune: 84% hydrogen, 14% helium, 3% methane Ammonium is not significant in any of the planets. Their blue-green color is due to the fact that methane absorbs in the red and thus the planets only reflect the blue-green.

Weather on Uranus and Neptune Uranus as few cloud structures and those can only be seen with the aid of computer enhancements. a) True color b-d) computer enhanced

Neptune shows more distinct cloud features than does Uranus Neptune shows more distinct cloud features than does Uranus. It even has giant storms that last a while (few years) much like Jupiter. Neptune has the great dark spot instead.

Interior Structure Since there is no surface to the Jovian planets we can’t set up seismic observations, how do we know about their interiors? We use computer modeling. Since the Jovian planets are made mostly of the simple gasses of hydrogen and helium, we think we understand how they behave.

It is the combination of a metallic hydrogen interior and high rotation rates that give the Jovian planets (especially Jupiter) their strong magnetic fields. This magnetic field channels the solar wind around the planet and spacecraft can measure its effects far from the planet.

The one bad thing about being the largest planet in the solar system is that you tend to attract a lot of comets and meteors. Visible Scare Infrared Image Breakup of comet Shoemaker-Levy 9