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The Asteroid Belt and Outer Planets of the Solar System

Updated on June 20, 2012
Solar system with sizes to scale. Distances hugely compressed.
Solar system with sizes to scale. Distances hugely compressed. | Source

Facts About the Solar System

  • All of the outer planets (Jupiter, Saturn, Uranus and Neptune) have rings
  • The solar system is thought to extend for almost 2 light years
  • Most objects orbit the Sun in an anti-clockwise direction - Halley's comet orbits in the opposite direction

The Asteroid Belt

The Asteroid Belt is the line that separates the inner and outer solar system. Planets 'inside' the Asteroid Belt are known as 'Terrestrial' planets - they are rocky worlds with a metallic core; they are also small. 99% of the mass orbiting the Sun is contained within those planets outside the Asteroid Belt: the Gas Giants.

The Asteroid Belt is debris left over from the formation of the solar system. Another theory is that the Asteroid Belt is the remnant of a planet that was destroyed in a massive collision. These chunks of rock can range anywhere from a few metres across to several kilometers wide or even bigger. The largest body in the Belt is Ceres: at 950km across, it has recently been reclassified as a Dwarf Planet - the same as Pluto.

Asteroids are rich in many economically important rare-earth metals and minerals. So rich in fact, that there is (tentative) talk of attempting to trap Asteroids that travel near Earth (so-called Near Earth Asteroids) to mine them.

Outer Solar System - the Gas Giants

The four gas giants comprise 99% of the mass orbiting the Sun. From top to bottom: Neptune, Uranus, Saturn and Jupiter.
The four gas giants comprise 99% of the mass orbiting the Sun. From top to bottom: Neptune, Uranus, Saturn and Jupiter. | Source
The largest planet in our solar system. You can see the shadow of Europa in the bottom left. Jupiter is one order of magnitude smaller than the Sun, and one order of magnitude larger than Earth.
The largest planet in our solar system. You can see the shadow of Europa in the bottom left. Jupiter is one order of magnitude smaller than the Sun, and one order of magnitude larger than Earth. | Source

Jupiter

Jupiter is the largest planet in our solar system - in fact, if it was much larger, it would have fired up into a second star! Jupiter lies just beyond the Asteroid Belt and is the first of the Gas Giants.

Jupiter is made mainly of hydrogen and helium (like the Sun) and has no solid surface. Jupiter's moons - of which it has over 60 - are almost a mini-solar system in themselves. Jupiter has moons with active volcanoes (Io), with their own magnetic field (Ganymede), and even with potentially liquid oceans (Europa)

Jupiter is perhaps best known for it's Great Red Spot - a storm the size of the Planet Earth that has been raging for over 300 years.

Fast Fact: Although Jupiter is 318 times the mass of Earth, due to its low density, the surface gravity is only 2.5 times greater than on Earth!

Perhaps the most beautiful planet in our solar system - Saturn. The picture was taken by Cassini on approach in 2004
Perhaps the most beautiful planet in our solar system - Saturn. The picture was taken by Cassini on approach in 2004 | Source

Saturn

Ask someone what their favourite planet is and the answer is most likely Saturn. Saturn has the largest and most complicated ring system in the solar system. When first observed by Galileo, he drew the rings as separate spheres; Galileo dubbed it to be 'triple-bodied'

Saturn is made of mainly Hydrogen and Helium. It's rings, although they appear solid, are made up of countless particles of different sizes. These particles are mostly made of water ice and can be anything from a few micrometers across to several metres. Two of Saturn's moons orbit in gaps between the rings.

Fast Fact: Every 15 years, Saturn aligns in such a way that it's rings cannot be seen from Earth (they are so thin that when "side-on" we can't see them) This is next due to happen between 2024-2025.

The lopsided giant - Uranus also has rings (although not visible in this shot taken by Voyager 2 in 1986) and the brightest clouds in the solar system
The lopsided giant - Uranus also has rings (although not visible in this shot taken by Voyager 2 in 1986) and the brightest clouds in the solar system | Source

Uranus

Uranus was discovered in 1781 by William Herschel. It gets its blue hue from methane mixed in with the hydrogen and helium that make up most of the planet.

The extreme tilt of the planet (see below) is thought to be due to a massive collision with another planet early in the history of the solar system. This means that the rings of the planet are perpendicular to the direction of motion - at first glance they appear to circle from North to South poles.

Fast Fact: Uranus is the only planet to rotate on its side - it has an axial tilt of 97.9°. This means that after 21 years of normal day and night, there would be 21 years of day in the Northern Hemisphere, followed by 21 years of normality, followed by 21 years of night!

Neptune is the most distant planet from the Sun. Visible is the Great Dark Spot - a massive storm similar to that seen on Jupiter.
Neptune is the most distant planet from the Sun. Visible is the Great Dark Spot - a massive storm similar to that seen on Jupiter. | Source

Neptune

A twin planet to Uranus, this planet is the most distant of the Gas Giants. Despite it's titanic distance from the Sun, Neptune is actually slightly warmer than Uranus. With very similar compositions, it is unclear why Uranus and Neptune have different colours. It is also unclear what is driving the immense storms in Neptune's atmosphere - given it's huge distance from the Sun and correspondingly small energy input.

Neptune has a number of moons. The largest, Triton, actually orbits the planet in the opposite direction to Neptune's rotation. Triton is also the coldest object yet visited in the solar system with temperatures recorded at an icy -235°C

Fast Fact: The winds clocked on Neptune are the fastest anywhere in the solar system, reaching a peak of over 2100 kph!

Outer Solar System - Facts and Figures

Fact
Jupiter
Saturn
Uranus
Neptune
Mass (Number of Earths)
318
95
14.5
17
Diameter (km)
142,984
120,536
51,118
49,500
Distance from Sun (Million km)
778
1,426
2,870
4,498
Time taken to travel around Sun
11.86 Years
29.45 Years
84 years
164.8 years
Time taken to spin on Axis
9.9 hours
10.656 hours
17 hours
16 hours
Average Surface Temperature (°C)
-148
-178
-216
-214
Moons
50 confirmed, 14 provisional
53 confirmed, 9 provisional
27
13
Comparison of the characteristics of the outer solar system celestial objects

A Tour of our Solar System

Should Pluto still be a planet?

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Pluto: a Dwarf Planet

For an object to be considered a planet it must satisfy a number of criteria:

  1. It must orbit the Sun
  2. The object must be large enough that its gravity shapes it into a sphere or oblate spheroid
  3. Must not be a satellite (moon) of another planet
  4. Cleared its orbital path of debris

It was decided by the International Astronomical Union that Pluto did not satisfy the final criterion. It was thus demoted in 2006 to the newly created category of "Dwarf Planet" along with Eris (which has an eccentric orbit far beyond Neptune) and Ceres (an Asteroid Belt object that has been reclassified).

Pluto still holds a special place in the solar system, however. Any object that meets the criteria for a Dwarf Planet that orbits beyond Neptune is designated a Plutoid.

An illustration of the outer reaches of our solar system, including the two Plutoids: Pluto and Eris, as well as the Kuiper Belt
An illustration of the outer reaches of our solar system, including the two Plutoids: Pluto and Eris, as well as the Kuiper Belt | Source

Beyond Neptune: The Kuiper Belt and Oort Cloud

Far beyond the orbit of Neptune lie two clouds of dust, debris and rock: the unused spare parts left over from the birth of the solar system. The birthplace of many comets, the Kuiper Belt and Oort Cloud are icy discs that mark the very edges of our solar neighbourhood. Very little is known about this distant region of space (although still our backyard in cosmological terms). NASA intends to address this gap in our knowledge through the New Horizons space probe, launched in 2006. This probe will explore the Kuiper Belt and Oort Cloud after a rendez-vous with Pluto in 2015.

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    • TFScientist profile image
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      Rhys Baker 4 years ago from Peterborough, UK

      FYI this is my 50th hub! :)

    • alliemacb profile image

      alliemacb 4 years ago from Scotland

      Congrats on 50th hub. It's really interesting. I always loved learning about the solar system when I was in school and you provide great information here.

    • Marcy Goodfleisch profile image

      Marcy Goodfleisch 4 years ago from Planet Earth

      Congratulations on your 50th hub! You always have such amazing and interesting topics. This is outstanding - I love the details and the photos you selected. I'd heard about Pluto being demoted - it's always had a rather dark and mysterious attraction for people; maybe this will help alleviate those thoughts. It is a bit of a change to think that we can't say we have nine planets now. Eight and a half?

      Thanks for this educational hub! Voted up and up!

    • wayseeker profile image

      wayseeker 4 years ago from Colorado

      Way cool stuff here, TF. I love astronomy, so much of what you discussed here is things I knew going in, but there are definitely some new things (Eris?--cool) and I'm particularly fond of how simple it is to follow. I'll be sending my daughter here to check out the solar system!

      Congrats on hitting 50, it's a worthy hub to fill that place.

      Best,

      wayseeker

    • mwilliams66 profile image

      mwilliams66 4 years ago from Left Coast, USA

      Congrats on posting your 50th hub. I myself am only 49 away from reaching that milestone.

      This is a wonderful educational trip through our solar system. Thoroughly enjoyable to read and chock full of fascinating information.

    • f_hruz profile image

      f_hruz 4 years ago from Toronto, Ontario, Canada

      Congratulations to another very informative hub!

      I had to watch the video on YouTube and was exposed to a brand now environmental promo about a great project right here in Toronto ... :)

      Franto in Toronto

    • TFScientist profile image
      Author

      Rhys Baker 4 years ago from Peterborough, UK

      @allie: Space is one of everyone's favourite topics I think. It is fascinating - I'm glad you enjoyed the hub

    • TFScientist profile image
      Author

      Rhys Baker 4 years ago from Peterborough, UK

      @Marcy: I can officially say that "When I was young we had NINE planets." to my children! Thank you very much for your effusive praise - I'm glad I could teach you something fun.

    • TFScientist profile image
      Author

      Rhys Baker 4 years ago from Peterborough, UK

      @wayseeker: I too had not heard of Eris when I started researching this hub. It wasn't until I decided to write about Pluto that I thought to research other Dwarf planets.

      I hope your daughter enjoys the hub - don't forget I've done the inner solar system too ;)

    • TFScientist profile image
      Author

      Rhys Baker 4 years ago from Peterborough, UK

      @mwilliams: that milestone will creep up on you faster than you know - I've only been here 5 months and have hit it already - and that's in addition to exams, revision and homework marking!

      I'm glad you enjoyed the hub - I hope you learnt something new?

    • cclitgirl profile image

      Cynthia Calhoun 4 years ago from Western NC

      What a fantastically well-done hub, TF. You covered facts that I didn't know and it's always fun to learn a little more about the planets and fast facts. Thanks for an entertaining read!

    • profile image

      Barry 4 years ago

      There's no way the solar system is 2 light years big!!

    • profile image

      Barry 4 years ago

      Nevermind, it appears as though you're right, the oort cloud must be massive and thin. Can't wait till we start mining near-by asteroids. Maybe we'll be moving on to the oort cloud by next millennium!? Robotic space mining is gonna change everything!

    • profile image

      2 years ago

      This will help me with projects

    • profile image

      2 years ago

      and if you ask me who I am, you are not going to get anything except a riddle

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