Published on May 31st, 2011 | by Yellow Magpie0
The Outer World Of The Jovian Planets
It is an environment alien to our home-world. A place whose scale is frighteningly large. Dominated by the four gas giants, the vastness of the Solar System’s Outer World is just one part of the story.
There are four planets that monopolise the far reaches of the outer Solar System. These are Jupiter, Saturn, Uranus and Neptune. Together these are called either the Gas Giants or the Jovian planets after Jupiter.
These planets form two distinct types, Jupiter and Saturn are gaseous worlds with a liquid or solid core while Uranus and Neptune have frozen interiors.
Both are composed of different materials. Saturn and Jupiter are comprised almost exclusively of hydrogen and helium while Uranus and Neptune consist of frozen hydrogen, helium and methane.
The gas giants of Jupiter and Saturn and the ice giants of Uranus and Neptune have greatly shaped their world and played a critical role in the formation of the Solar System.
A Giant Formation
There are many theories as to how the four giants formed. One theory is that a portion of the original rotating gas clouds broke away to form the giants through the process of coalescence. The vast bulk of the rotating clouds would go on to form the Sun while our star was in a nebula or stellar nursery.
Another proposal by scientists is that the terrestrial rocky worlds formed before the giants. The gravity of the terrestrial planets then drew in huge clouds of helium and hydrogen and the Jovian system was created.
It is believed that Saturn and Jupiter formed in a region that was slightly more abundant with hydrogen and helium than Uranus and Neptune. Added to this, is the fact that in the area where the two distinct systems formed was divided between abundant and rare pure hydrogen.
With Saturn and Jupiter pure hydrogen was common while with Uranus and Neptune it was comparatively rare. In the latter’s case, icy chemicals were more readily available.
The Ring World
One of the most interesting aspects of the Jovian planets is their rings. Although Saturn’s rings have garnered much of the attention, each of the four planets have their own ring system.
Planet Jupiter’s, the hardest to see, is made up of dust and tiny particles. Saturn’s rings consist of highly reflective icy satellites which are composed mainly of water. The rings of the two ice giants, Uranus and Neptune, are composed of frozen methane which reflects far less light than Planet Saturn’s frozen water.
The perfectly circular shape of the rings along the equatorial plain of the planets is due to astrodynamics or orbital mechanics. Eccentricity is removed over time due to the enormous pull of the planet’s gravity and the objects themselves bumping into one another. Even the objects just settle into a routine, circular orbit.
A Question Of Distance
Separated by the asteroid belt, the Jovian planets are quite a distance from the Sun and indeed the Earth. At the farthest extreme, planet Neptune is 19.2 AU from the Sun. (AU stands for astronomical distance. One AU is the distance between the Earth and the Sun.)
Planet Jupiter, the closest of the giants, is still five AU from the Sun, four AU from the Earth.
A Landscape Of Moons
Although the terrestrial planets have satellites, they are paltry in comparison to the numbers of the Jovian worlds. The satellites range from minute particles to moons that rival the terrestrial planets in scale.
In essence, each of the gas giants has a mini Solar System. If you imagine the planet to be a Sun, you can see the pattern of the Solar System being repeated over and over in the four planets. The moons vary in size and get larger as they go out farther until gradually the satellites start reducing in size.
Also orbiting the giants are irregular satellites which are thought to be rogue asteroids which got trapped in the pull of the planets. However, planet Neptune differs greatly from these observation and is an exception. Yellow Magpie will later look at this in a separate post.
Full Of Debris
The world of the giants is also cluttered by asteroids and comets that have been sucked in by the gravitational pull of the Jovian planets.
The Trojan asteroids have been collected by planet Jupiter and now share its orbit after hundreds of millions of years of being perturbed by the largest planet.
Centaurs are thought to be passing comets which have been trapped by the planets. They are mainly composed of ice and dust.
Highly Recommended Reading
Check out Yellow Magpie’s Mars’ Volcanoes: A Stunningly Mysterious World With Colossal Vents for a more detailed discussion of this wonder of the Solar System.
You may also like to read The Planet Mars: Our Infatuation With The Red Neighbour and Mars’s Moons: The Oddness Of Phobos And Deimos.
You also wish to take a gander at The Solar System And Beyond: A Guide To The Cosmos.
Cosmos is a highly recommended book. It contains large, full-page pictures of Mars and writing on the subject by the highly competent author, Giles Sparrow.
For people living in Ireland or the United Kingdom, you can access: Cosmos from here.
For those who live in Canada, you can obtain: Cosmos here.
For Germany: Cosmos.
For France: Cosmos.