A Planet of Superlatives...
Within our Solar System, Jupiter is quite
frankly a planet of superlatives. It is the biggest, mightiest, most impressive
planet in our neighbourhood. It has two and a half times more mass than all of the other planets put together,
and over 1000 times the volume of the Earth. In some ways, it even bears some similarities with a small star. Scientists
calculate that in fact if Jupiter had been 50 times more massive than it is now, the pressure and temperature
in its core would have been sufficient to start nuclear reactions, thus turning it into a star.
Thankfully for us here on Earth however, this was not to be, and instead we are left with Jupiter as
'merely' the largest planet in the Solar System. However, Jupiter still appears fairly bright due to its size,
and is the 4th brightest object in the night sky. It was because of this brightness that Galileo Galilei was able to
spot this planet shortly after turning his newly refined telescope to the stars, from his home in Padova, in 1610.
He also discovered what are now known as the four 'Galilean moons' of Jupiter: Io, Europa, Callisto and Ganymede,
all of them rather unique in their own right. If you want to see Jupiter at night, it appears as a yellow-white
disc in the night sky.
Storms & Atmosphere
|Great Red Spot & another storm|
As one might guess from looking at the photos we have of it, Jupiter is a very active planet.
A plethora of storms rage all over its surface, the most famous being the 'Great Red Spot'. This is a gigantic rotating storm,
wider than 3 'Earth diameters'. It is highly complex and moves in a generally anti-clockwise direction, and historical records of Earth-based observations show that is has existed for at least 100 years.
The stripes which are visible on Jupiter's surface are caused by streams of fast, powerful winds which blow at over 400mph
alternately in opposite directions across the planet (along the east-west axe). These winds are thought to be mainly caused by
the internal heat generated from within Jupiter, and they can rapidly change shape, within days or hours.
Core & Magnetic Field
Jupiter's atmosphere is thought to extend a long way down into the planet. Nonetheless, scientists believe that
Jupiter does have a small, rocky core at its heart, surrounded by an inner mantle of metallic liquid Hydrogen, and an outer one of
'normal' liquid Hydrogen and Helium. Under the kinds of enourmous pressures generated in the heart of Jupiter, Hydrogen is
compressed to such an extent that it turns into liquid metallic Hydrogen (ie a mass of ionized protons and electrions).
|Jupiter by Voyager 1|
In fact, electrical currents running through this liquid metallic Hydrogen core are what generate
most of Jupiter's massive magnetic field, which is abnormally large, even for a planet Jupiter's size.
It stretches into space for millions of miles, and the electric activity is so strong that it pumps
billions of Watts every day straight into the Earth's own magnetic field.
Despite having a diameter 11 times bigger than the Earth's, Jupiter
spins on its axis faster than any other planet in the Solar System. This is why it bulges
out at the equator. This rapid spinning is also thought to contribute to the powerful wind systems which form
the clearly visible 'bands' on Jupiter's surface discussed above.
Other than the Sun, Jupiter is the largest emitter of heat in the Solar System. It is thought that this heat
is energy left over from the high-temperature formation of the planet. Radiation is slowly emitted in the infra-red,
and causes the planet to gradually decrease in volume, albeit by an insignificantly tiny amount.
Jupiter's thin line of rings were only discovered by the Voyager 1
space probe in the late 1970's. They are 5920 kilometres wide and 1 km thick. This was a
totally unexpected discovery and more recently it has been discovered there are in fact 3
sets of rings. At the last count, Jupiter had 63 moons. The first-discovered few are: Metis, Adrastea, Amalthea, Thebe , Io, Europa,
Ganymede, Callisto, Leda, Himalia, Lysithea, Elara, Ananke, Carme, Pasiphae and Sinope.
Click here to go to the Io section, for more information and pictures of Jupiter's most explosive moon - Io.
Here is a summary of Jupiter's Galilean moons:
This is the largest moon in the Solar System, larger even than the planets of Mercury and Mars.
It is believed to consist mainly of ice and slush.
Rather a nondescript moon this one, apart from quite a few crators, including
Valhalla, which is cool 3,000km wide.
The most active volcanic body in the Solar System, Io is by far the most
impressive of Jupiter's moons, and the most explosive, spewing gasses and dust over
30km above it's surface at speeds of up to 1km/second.
For more info & images of Io click here.
Europa is easily identifiable by the red cracks criss-crossing its surface. These
are in fact cracks in the smooth ice that covers the whole moon. Europa has enough
internal heat to have seas of liquid water below its surface, making it the most likely
body (other than the Earth) to harbour life in the Solar System.