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The Nebula Theory

Let's Get Together

If the blob of stuff gets big enough, it forms a sphere or ball. The center of gravity of the sphere is in the middle. Everything is being pulled towards the very center of the sphere. If enough material is pulled toward the center, the weight of the outer parts crush the inner parts and cause the atoms to fuse, or join together to become newer, more complex atoms. This process is called fusion.

What About the Leftovers?

Whatever parts are not used to make the new atom are released as heat and light energy. Whenever atoms are fused or split, they release a lot of energy. That is how atom bombs work. That is also how stars works. Stars are not on fire in space, they are constantly having nuclear explosions. This is what makes them shine.

Here Comes the Sun

When our Sun formed from a nebula in this region of space, it gobbled up nearly all of the material for itself. The key word here is “nearly”, which means that some material was left over after the Sun was created. However, if the mass of the solar system was converted into one dollar, the Sun would be worth more than 99 cents, and all the planets, moons, asteroids and comets put together would total less than one penny!

Solar Winds

As the Sun shines, it generates what is called a solar wind. It is not wind as we know it where air moves around – because there is no air in space. It is a flow of energy outward from the Sun that acts like a wind and pushs things outward.

When the Sun grew large enough and started shining through nuclear fusion, the solar wind it created blew the remaining nebular material outward. The planets, moons asteroids and comets condensed from this leftover material in much the same way that the Sun formed – from gravitational attraction pulling nearby available material together. Heavier elements remained closer to the Sun and lighter elements were blown further out.


Density of the Planets

Solar SystemThis explains why the inner planets of Mercury, Venus, Earth and Mars are dense, rocky planets and the outer planets of Jupiter, Saturn, Uranus (which, by the way, is properly pronounced ’YUR-uh-nis’) and Neptune are gas giants. Pluto, while still called a planet, resembles more closely the body of objects being classified as Kuiper Belt Objects. These distant objects are more like giant comets and are apparently made of materials light enough to be blown out past Neptune’s orbit.

Pluto and Beyond

This image shows the newly discovered planet-like object, "Sedna," in relation to other bodies in the solar system, including Earth and its Moon; Pluto; and Quaoar, a planetoid beyond Pluto that was until now the largest known object beyond Pluto. Sedna is bigger than an asteriod, but smaller than a planet. It is three times farther away from Earth than Pluto and is the reddest object in the Solar System, after Mars. 

     Not in this picture is the more recently discovered "tenth planet", 2003ub313, that is estimated to be larger than Pluto, perhaps around the size of the Moon.  See the "Big Bang Theory" page for more about this discovery.

(Click on the image for a closer look.)
Image Credit: NASA/JPL-Caltech


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