Jupiter was a ‘rolling stone’! – Part1

You may marvel at Jupiter—now very visible overhead, between 9:00 and 11:00 p.m.But there’s more to this high-profile planet, than meets the casual observer’s eye. Behind its pearl-like luster, and placid persona, is a turbulent cosmic past.

In a cogent lead to her 2011 news release, the United States National Aeronautic Space Agency (NASA’s) Elizabeth Zubritsky put it this way: “Jupiter, long settled in its position as the fifth planet from our sun, was a rolling stone in its youth”.

The archetypical “rolling stone,” in the Black blues tradition, doesn’t gather any moss: He moves from town to town and woman to woman, never accumulating wealth or raising a family.

Jupiter was, in one sense, true to this archetype. In its early years, it migrated from the outer to the inner solar system and back again—stunting the growth of Mars, in the process, and robbing a probable fifth rocky planet of its future.

Unlike the African American folk character though, Jupiter has gathered plenty of cosmic “moss”. It possesses more than twice the mass of all the other planets combined and currently heads a family of 67 moons!

Jupiter is usually the third brightest object in the night sky, after the Moon and Venus. Mars can, on rare occasions, upstaged the giant, when the Red Planet is in perihelion and opposition. But while Mars is currently coming on strong, Jupiter is clearly reigning from its dominant position, directly overhead.

Remember, you’re looking 650 million km into space. From that distance, it’s not apparent that, size-wise, Jupiter ranks second to the Sun. More than 1000 Earths could fit into its space. In fact, astronomers sometime joke that the solar system consists of Jupiter, the Sun and other debris!

Like they used to say about Texas, U.S.A., almost everything concerning Jupiter is big. Its four largest moons are planetary in size. One, Ganymede, is the largest satellite in the solar system (its diameter exceeds that of the planet Mercury) and two (Callisto and Ganymede) are much bigger than our Moon.

Despite its hugeness—143,000 km at the equator–Jupiter rotates faster than all the other planets, with a Jovian day passing in just under 10 hours. It also has the most powerful gravitational field (which has helped shape the history of the solar system) and the strongest magnetic field.

Chemically, Jupiter exhibits an affinity with the Sun, which consists mainly of hydrogen and helium.Says the Teach Astronomy module, “Jupiter has a bulk internal composition of roughly 2/3 hydrogen, with the rest being helium mixed with small amounts of rocky silicates, metals, and other impurities”.

The solar system has four terrestrial (or rocky) planets, which are nearest the Sun, while the four outlying bodies are gaseous. The outer planets used to be called “Gas Giants”. But most astronomers now restrict that term to Jupiter and Saturn. They refer to Uranus and Neptune as “Ice Giants”.

Katharina Lodders, of Washington University (St. Louis Missouri), still uses the old term: But notes, nevertheless, that “The larger and gas-rich giants Jupiter and Saturn [contain] more than 50 mass % H and He, and the smaller gas-poor giants Uranus and Neptune…less than 50 mass % H and He”.

As if Texans weren’t jealous enough, Jupiter boasts the biggest ocean in the solar system. But it’s an ocean of liquid metallic hydrogen—not water. At a depth of 20,000 km, says Teach Astronomy, loose electrons “flow freely and could carry an electric current, like a metal”: Hardly a place to go for a swim!
*To be continued.