Gas Giants

[Jim Colyer]

Voyager 1 flew by Jupiter and Saturn and was deflected. Voyager 2 went on to Uranus and Neptune. Voyager 2 spent 12 years (1977-89) on its Grand Tour. All the gas giants were found to have rings.

Jupiter is a failed star. If it were larger, nuclear reactions would have begun and it would shine by its own light. It is made of hydrogen and helium, the most common elements.

Jupiter has bands because it rotates so fast that its clouds are stretched into patterns. The Great Red Spot is a huge storm. There is now a Red Spot Jr. The Galileo probe reached Jupiter in 1995.

Jupiter has 60 moons. Io, Europa, Ganymede and Callisto are the largest, named for Jupiter's lovers. They were first seen by Galileo, who invented the telescope in 1610. Io is interesting because it has the only volcanos in in the solar system beyond Earth.

Saturn is a butterscotch ball of gas light enough to float in water. Saturn's rings are its glory. There are 7 main rings. They are made of rock and ice. As Saturn orbits the sun every 29 years, we see its rings open at the top, edge-on, open at the bottom and edge-on again.

Saturn has 31 moons. Titan is larger than the planet Mercury and is the only moon in the solar system with an atmosphere. Its atmosphere is orange and dense.

The major gap in Saturn's rings was discovered by Cassini. Titan was discovered by Huygens.

The Cassini-Huygens spacecraft is the first to orbit Saturn. The probe descended into Titan's atmosphere and sent back data. The reason for studying its atmosphere is that it is thought to be similar to that of early Earth. Scientists want to know how life developed. $3.3 billion was spent on Cassini. It is mind-boggling, the money spent on these projects.

Uranus was knocked on its side. Modern astronomy is explained in terms of collisions. Consider that dinosaurs were killed off by an asteroid. If the ancients thought the heavens benign, today's universe is a violent place. Uranus is a green, featureless pool ball. It was discovered by William Herschel in 1781.

Voyager 2 photographed Neptune's Great Dark Spot in the blue methane.

Small, rocky Pluto at the edge of the solar system breaks the rules. Its orbit is erratic, bringing it inside Neptune. Pluto may have been a moon dislodged from somewhere else. It has a companion, Charon. Clyde Tombaugh discovered Pluto in 1930. NASA launched the New Horizons spacecraft in January, 2006. It will take nearly 10 years to reach Pluto at a distance of 3 billion miles. Pictures will arrive in 2015. I will be here.

The Voyagers have left the solar system and are on their way to the stars. They contain records of earth sounds, languages and music.

ASTRONOMY http://jimcolyer.com/papers/entry?id=2