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Jupiter, Wielder of Thunderbolts - By Nick Kollerstrom  |
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Fact File: Diameter: 143,000 km Distance to Sun: 5 AU Solar Orbit: 11.9 years No of Moons:16 |
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Jupiter whirls round at a
colossal speed of one rotation per ten hours, faster than anything else in the
heavens: yet it's the biggest planet of them all. The little planets, Mercury
and Venus, turn so slowly, taking months to go round just once, but Jupiter does
it in hours! It thereby generates its huge magnetic field, which would appear in
the sky as larger than our Moon, if we could see it. The tail of its
magnetosphere stretches out well beyond Saturn, so that the latter enters into
it every time it conjuncts Jupiter. Jupiter does wield huge lightening-bolts,
after all. Modern satellite-reconnaissance craft have ascertained this. 'Lightning bolts illuminate the Jovian night sky with enough energy to vaporise a city. Everywhere there is stormy weather as clouds billow, churn and surge above a vast sea of hydrogen. The colourful spots, zones and belts are weather patterns. In fact, nearly everything we see on this awesome planet is a storm cloud' (1) |
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Magnetosphere of Jupiter:-
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The story of this discovery goes back to 1955,
when radio interference due to a Jupiter magnetic storm was first
detected. This was at first assumed to be due to a nearby car motor,
for who would suppose that such an effect was coming from something
a million miles away? No-one expected storms to be happening on a
distant planet. Jupiter's radio-wave emissions normally occurred, it
was found, in a series of short bursts: "to many radio astronomers,
it almost sounds like the kind of radio noise made by lightning
storms on earth"
(2) |
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Detail of Jupiter's atmosphere, as imaged by Voyager 1.
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It turned out that storms emanating from Jupiter were related to the small, inmost satellite, Io. When Io is in a direct line between Sun and Jupiter, emissions are much weaker than when Io is 90� off the Sun-Jupiter line (3). i.e. storms maximise at Io-Jupiter-sun squares. How could little Io manage this? Io, no bigger than our Moon, is volcanically active, more than anything else in the solar system, and the severe stresses and strains of its role produce this volcanism. When voyager flew by in 1979, astronomers were staggered to see photographs of volcanoes erupting. As Io moved behind Jupiter into the dark, it remained visible, by the light of its active volcanoes. |
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Io:
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The Voyager I spacecraft which set off in 1977 was maybe the most successful space project ever launched. It reached Jupiter in 1979, having been constructed to function within the enormous magnetic and high-energy electric fields of Jupiter. It would even "...be able to detect bursts of radio waves from single lightning strokes in the Jovian atmosphere" (4) |
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But, nothing had prepared
astronomers for the breathtaking weather system on this giant gas world - or its
huge retinue of moons which were no less diverse and exciting. Jupiter's cloud
features intermingle in an intricate manner, seeming to pass through each other
without mixing. The Voyager data on Jupiter was majestic and beyond expectation:
'Windswept clouds churn and seethe in Jupiter's colourful atmosphere. Huge
storms larger than the Earth in size swirl across Jupiter, while giant cyclones
create continent-sized spots. Smaller spots chase each other, whirling and
rolling about, and even devouring each other. Zones and belts race around the
huge planet, driven by hurricane-speed winds. Jove's brilliant colourations
were due to continuous lightning cascades in the atmosphere
(5). "The
dark side of Jupiter also revealed intense lightning storms all over the
place... these may be responsible for Jupiter's fantastic colouring" The data
collected surpassed everyone's expectations - indeed it had been some time since
anything made astronomers feel so jovial. |
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Figure 1:
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Figure 1 shows the several groups of moons that orbit Jupiter, aren't they splendid? While looking at them, we may be reminded of Jupiter-associated keywords: optimism, buoyancy, expansion, confidence and wellbeing. It could be that any feelings we get from contemplating these busy groups of moons are more important than theories about them, for example how they got to be like this. The nearer moons orbit in the plane of its equator, which indicates that they were derived from Jupiter, and that includes the four big ones that Galileo discovered. We are shocked to see that the outermost group of Jupiter-moons orbiting in the reverse direction to Jupiter's rotation and all the other moons. With its fine array of moons, Jupiter shows the importance of keeping things in a proper balance. |
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Jupiter shares its orbit around the Sun with two groups of captured asteroids, called the 'trojans.' Gravity holds them captive. They never collide because each group stays a one-sixth division of the orbit away from Jupiter (6). "The two groups of 'prisoner planets,' whose movements are otherwise entirely subordinated to those of Jupiter, swarm restlessly within a small space, as though to compensate for their loss of freedom." (7). The second diagram shows a hexagon-based construction linking Earth's orbit with Jupiter, and its pattern links these asteroid-swarms to Jupiter (8). |
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The four moons of Jupiter
that Galileo discovered through his telescope in 1609 were Io, Europa, Ganymede
and Callisto. In the best-selling book he published about these, The Starry
Messenger, he named them after his patron Cosimo de Medici, explaining that he
had Jupiter at his MC, i.e. at the top of his natal horoscope. And so they
became called the Stella Medici. In the foreword of his book he described to his
patron, seven gleaming attributes of Jupiter:- |
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"Who does not know that clemency, kindness of heart, gentleness of manners, splendour of royal blood, nobleness in public functions, wide extent of influence and power over others all of which have fixed their common abode and seat in your highness - who, I say, does not know that these qualities, according to the providence of God, from whom all good things do come, emanate from the benign star of Jupiter?" (9)
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The periods of the three inner Galilean satellites are synchronised to a 1:2:4 ratio, so that little Io goes round four times each time Ganymede revolves once. Astronomers take this as their prime example of resonance working in our solar system. Also, these Galilean satellites move round with synchronised rotation, ever facing Jupiter. One may gain a reassuring sense of stability and harmony from these Jovian orbits. As these three Jupiter-moons whirl around their parent planet, they always maintain a beautiful resonance: whenever two of them come together, into a conjunction, then the third will be directly opposite to them, or else in square to them. See how this happens here. Thus a strong square structure is forming and reforming in space around Jupiter - that contrasts with the one-third angle we saw earlier, measured out by the 'Trojan' asteroids, that are held captured in the same orbit as Jupiter. |
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Quiz question:
of the Galilean moons of Jupiter, which one is the prettiest? Answer: Although Callisto has a nice sparkly texture:- |
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I think Ganymede is the best:-
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Sun Rings by Terry Riley, 2003, is music using Jupiter-sounds.
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