Universe Guide


A Planet is a celestial body that orbits round a star such as the Sun. For a long time, there had been no consensus on what constituted a planet until August 2006 1 when the International Astronomical Union came up with a definition of what a planet was. For an object to become a planet, it had to fulfil all the following three criteria.

The planet Pluto which had at that time been known as a planet was downgraded. Instead of being downgraded to an asteroid, it became a dwarf planet. A dwarf planet is a small planet that fails the third test. The asteroid Ceres which is in orbit around the sun between Mars and Jupiter was upgraded from asteroid to dwarf planet status. Clearing the neighbourhood means that it doesn't cross other planets or asteroids in its wake which as Pluto is in the area of known as the kuiper belt and crosses many paths, it failed.

A planet can be classified as either a Rocky Planet (Earth), a Gas Giant (Jupiter), a Dwarf Planet (Eris) or an Extrasolar planet. An extrasolar planet is a planet that orbits a star other than our own Sun. Again, an extrasolar planet can be either Rocky, Gas or Dwarf. We have been discovering planets orbiting round other stars but the majority of those have been Gas Giants, ones that life could not possibly exist on because there's no water or any land or atmosphere in which to survive.

Whilst in our solar system, the rocky planets are closest to the Sun and the gas giants are on the outside, it shouldn't be taken as a rule. There are many exoplanets that are gas planets which orbit close to their stars. According to the Gemini Observatory, there are gas giants that cling to their stars. 9

It is not a case of size whether an object is a moon or a planet or an asteroid, the Moon Ganymede which orbits round Jupiter is larger than Mercury but is not a planet as mentioned, it orbits a planet and not a Star. The difference between an asteroid, a planet and a moon is that

Anatomy of a Planet

A planet does not have to have a moon to be a planet, Pluto has numerous moons but it is not a planet in the same sense as Earth is. Also Mercury has no moons but is a fully fledged planet like Earth. All the gas planets including Jupiter and Neptune have rings of dust, Jupiter's and Neptune's rings are just not as big as those of Saturn and Uranus. 4 A planet doesn't have to have an atmosphere but all the planets in our solar system has an atmosphere, either toxic or friendly including Mercury 5. Planets do not have the autonomy of atmospheres in , Titan, one of Jupiters moon has an atmosphere. The atmosphere will normally consist of Hydrogen, Helium, Oxygen (but not enough to breathe) and Nitrogen. On Earth, Nitrogen is more common in the atmosphere than Oxygen but its Oxygen that keeps us alive.

On Earth, all the land is on teutonic planets that are constantly on the move, they move so slow that you don't notice. Sometimes the movement causes an Earthquake when you do feel the earth move. Earthquakes can happen without anyone noticing except from very sensitive scientific instruments. When the Earth was very young, all the continents of the world were one giant continent called Pangaea6. In the future, far future to be precise, the continents will once again be one super continent7

Once you have gone through the atmosphere, you reach the land or crust then you need to work through the layers of the crust till you get to the core. It is believed every planet including the gas giants have a core, for Earth, we have molten iron core which generates the heat and produces the protective magnetic fields that protect us from the Suns harmful rays. As for the Gas Giants, it is believed there is an iron core at the heart of the planet. Due to the extreme pressure in the atmospheres, we have not just ventured into the inside of it.

How to build your own planet.

To create and build your own planet is simple in theory but before you go off in a space ship to find somewhere to build one, you need to know its extremely hard and time consuming. A planets life begins with death, the death of a large star, one that went supernova. After it went supernova, it would create a planetary nebula which over time would condense and coalesce. At the heart of the nebula would be a new star being born. As the star begins to form, so do the planets and other orbital objects. The following video put on youtube shows in graphical detail how a planet is created, the first half deals with the death of a star and the birth of the new star and planet. The film also include details about Panspermia, the believe we came from another place.

Creation of

It is said our Sun is a third generation star in other words, two stars lived and died before our Sun appeared. Whilst a star lives, it turns hydrogen to helium and then on to the next element in the periodic table. When it gets to Iron, it cannot transform anymore and as such explodes. Some of the elements that our bodies contain could only be created through the extreme heat of a dying star so the death of a star was imperative. In about five billion years time, our Sun will supernova and begin again as a new solar system.

Goldilocks Zone

The Goldilocks Zone is a region of space from a star which is neither too hot nor too cold for life to exist. It comes from the fairy tale 'Goldilocks and the Three Bears' where the little girl tastes the Bears porridge and finds one too hot, another too cold but one just right. The zone is also known as Circumstellar habitable zone. 2. The following picture is from NASA 3 which shows the Goldilocks Zone in respect to both Earth and an extrasolar planet known as Kepler 22b.

As you can see from the image, both Mars and Earth are in the zone but life as we know it only exists on Earth. Venus just misses out on being in the Zone, however, its atmosphere is highly pressurised and toxic, no life could ever possibly exist on the planet. Scientists have found life on Earth existing in the most inhospitable locations on Earth but Venus is just too extreme. Bacteria has been found in the upper atmosphere of our planet and there could just be life in Venus at the higher atmosphere where the pressure is low. 8

For years, we have speculated as to whether there is life on Mars and the best we can hope for is micro-organisms to be still present either in the atmosphere or underground. Mars has water in the Ice Caps in the North. Scientists have speculated that life once existed on Mars but not anymore because the atmosphere has turned inhospitable. Whilst Mars has an atmosphere, it is not oxygen bases and it doesn't have an electro-magnetic field protecting the surface from the Sun's harmful radiation. If we did as Kim Stanley Robinson wrote about in his Mars trilogy and colonise the planet, we would have to consider the thin protection that the planet provides. Mars does not have a magnetic shield that could protect any life from the harmful rays of the Sun. If we went to the planet, we would need to protect ourselves from the rays. When Neil Armstrong and the other astronauts went to the Moon, they were protected by the magnetic field from the Earth.

Goldilocks Zone of Kepler 22b and Earth

Planet X

Planet X refers to the unknown planet, for years, it was the associated with Pluto, the one time ninth planet. X doesn't refer to the number 10 as in Roman numerals, it refers to the unknown. There is a search out there looking for a new Planet-X, something that is lurking at the edge of the Solar System, something waiting to be discovered. Part of the search was instigated by the fact that something was affecting Uranus but it was not until voyager space probes reached the zone that the irregularities of Uranus were caused by a miscalculation in Neptune. Scientists are still searching for something out there beyond Neptune that could be a dark planet, after all Eris was not found until advanced telescope discovered it.

Rogue Planets

A rogue planet is a planet that doesn't orbit a star, this might sound implausible but they have been found to exist. How the planets came to be on their own is still to be decided. The only heat that would reach the planet is the heat that is generated from inside the planets core. The surface would be frozen or if its lucky very cold. The planet might have a liquid environment which could mean life existing in the darkness. The rather imaginatively named planet WISE 0855-0714 is the closest rogue planet to our solar system at a distance of 7 light years. As they do not orbit a star, they're discovered when they pass in front of a star. 11 In Star Trek - Deep Space Nine, the Changelings live on a rogue planet where they have sought sanctuary.

NASA Artists' impression of a Rogue Planet.

Moons, Planetary Satellites

All the planets in the Solar System except the inner most planets have moons. The larger the planet the more moons it has is wrong. Earth only has one moon but Pluto whether you refer to it as a planet or a dwarf planet is smaller than the Earth but has more moons.

The Moon that orbits our planet was created so the theory goes when a large celestial object called Theia smashed into the Earth in the early Solar System. Debris from the smash coalesced and formed our planet as we know it today. The collision is reckoned to have been about 100 million years after the Solar System was formed. Ref:U.C.L.A.

As mentioned before, Mars' asteroids are generally thought to be asteroids that came too close to planet and were grabbed and pulled into a orbital plane around the planet.

Planets aren't the sole celestial objects that can have moons. Asteroid 243 Ida is known since 1994 to have a moon in orbit around it.

Planetary Rings

All the gas giants in our Solar System have rings including Jupiter and Neptune. The four rocky planets don't have rings. The rings are tiny ice balls, dirt and rock that are held in place by gravity. Saturn is the most famous of the planets to have a ring system. Jupiters rings was discovered in 1979 when the Voyager 1 Space Probe discovered them on a fly past.

We've ruled out our rocky planets such as Earth and Mars having rings but there's nothing to stop exoplanets having rings. Science Fiction writers love to push the boundaries of their visions and there are some planets that have rings such as Geonosis in fiction.

List of Planets in the Solar System

PlanetPositionTypeDiscovererLength of Day (hrs)
Uranus7GasSir William Herschel17.24
Neptune8GasJohann Elert Bode16.11
Pluto9DwarfClyde Tombaugh153.282

Related Pages of Interest :-

Comments and Questions

There's no register feature and no need to give an email address if you don't need to. All messages will be reviewed before being displayed. Comments may be merged or altered slightly such as if an email address is given in the main body of the comment.

You can decline to give a name which if that is the case, the comment will be attributed to a random star. A name is preferred even if its a random made up one by yourself.

This website is using cookies. More info. That's Fine