History
It must have been fascinating in ancient times to gaze at the stars and speculate about what they are. Ancient astronomers called some objects in the sky "planets" because of the way they moved around the Earth. Planet means "wanderer" and they named the planets after Roman gods such as Mercury which means the god of trade and profit and Jupiter which means king of the gods.
There were many mathematicians and physicists who monitored the stars and made observations. Many of these astronomers collected their data at the same time other astronomers were collecting the same or similar data and this sometimes confirmed or refuted their data or previous collected data. Names like Copernicus, Kepler, and Newton come to mind. Copernicus was the first to realize that the Earth and planets orbited the Sun. Until then and even during his time it was thought that the planets orbited Earth. Kepler's contribution is the laws of how planets orbit the Sun and Newton's contributions are laws of motion that allowed for eventual space travel. Kepler's and Newton's laws are still prominent today. Mathematicians held high status in political circles and were sought to make predictions about celestial events such as eclipses. As the need for more exact measurements and describing more celestial events became essential so did the need for more sophisticated mathematics. And, derivatives soon followed to explain the various changes in the universe. It is unbelievable but true that new mathematics is sometimes invented in order to explain the events of nature.
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Today, there still exist many misconceptions about the solar system. There is recorded data
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that confirms that there are individuals who believe that Mercury is the hottest planet when in fact it is Venus because of its greenhouse effect. Their temperatures compare 425
o
C. to 470
o
C. Mercury has virtually no atmosphere and therefore the heat is not trapped about the surface as is the case with Venus which has a thick atmosphere.
Movies also reinforce misconceptions. A chase through the asteroid belt is more trilling if the asteroids are in proximity to cause collision than if they are at great distances as is the case. This wide distance between asteroids is how our space probes are able to travel out to distant planets and not be annihilated.
The Solar System
Looking at the solar system, there are eight planets. Pluto is no longer a ninth planet, it has been re-designated as a "dwarf" planet along with the asteroid Ceres and the outer solar-system object called Eris.
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Pluto's composition, first of all, never fit the characteristics of the other eight planets. It is mostly composed of rock and ice. Its orbit is not in the same plane as the other planets. Pluto's orbital inclination of 17.15
o
is higher than the almost collective pancake orbits of the other planets. The inclination of the orbits of the other planets range from 0.00
o
for Earth to 7.0
o
for Mercury using Earth as the base planet to measure all other planets against. (see Figure 1)
(image available in print form)
Figure 1
The
figure shows the orbits of Pluto and Neptune. The orbits of the other seven planets are in almost the same plane as Neptune. The orbital inclination to the ecliptic (Sun's path among the stars) ranges from 0.00
o
for Earth to 7.00
o
for Mercury. Pluto at 17.15
o
is obviously out of place. Figure may not be to scale.
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Source of figure is www.Wikipedia.org, and the figure is in the public domain.
All the planets orbit the Sun in the same direction and in more or less in the same plane. Their orbits are nearly circular about the Sun but have enough eccentricity to be elliptical as was shown by Kepler. (Kepler's Laws are reviewed below.) It is common knowledge that the Earth spins on a tilted axis and so do the other planets. One planet, Uranus, is tilted on its side and spins horizontally.
The Sun contains more than 99% of the total mass in the solar system. It is composed of 99.8% hydrogen and helium and .2% other elements. The Sun is hottest at its core where nuclear fusion occurs. The Sun is gaseous throughout with no solid surface or solid core.
The inner planets, Mercury, Venus, Earth, and Mars, are called terrestrial planets because they have rocky surfaces. Terrestrial means Earth-like and the four planets are all small, dense, have abundant metals, a few moons, and no rings. It is also interesting to note that the small cores of these planets are metallic.
The outer planets, Jupiter, Saturn, Uranus, and Neptune, are called Jovian planets because they are Jupiter-like. These planets are larger in size, have smaller densities, have many moons, and have rings. Some have prominent rings, others very fine rings. They are also called gas giants. As with the inner planets it is interesting to note that it is not exactly known what the core of these planets are composed of. It is suspected that the core could be composed of compressed carbon and be diamond-like
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. However, the gas giants do have a surface, though not a solid one. The planets' gravity holds together the gases about the core.
The formation of the solar system began 4.6 billion years ago and during that time the elements and debris that were strewn into the solar system formed into planets by crashing into each other. Eventually all the debris was either formed into planets or knocked out of the solar system by these crashes (see Figure 2).
(image available in print form)
Figure 2
Shown at left and then right is how the solar system must have looked at its beginning as debris and elements joined together by crashing or by gravity and created the celestial bodies. Some debris was knocked out of the solar system. Eventually, the planets cleaned out their areas. The ability to clean out respective planetary areas is a characteristic of planets. Source of figure: www.Wikipedia.org.
The resulting solar system was devoid of the numerous particles and the planets successfully cleared their areas. The only significant band of rocks in the solar system is the asteroid belt located between Mars and Jupiter (see Figure 3). What was left was an almost flat solar system (refer to Figure 1). The Sun is the main gravitational pull on the planets and holds them in place.
(image available in print form)
Figure 3
The asteroid belt between Mars and Jupiter was not cleaned out by the planets. It was sufficiently far enough away from Mars and Jupiter not to be absorbed by either of them. Also, the Sun's gravitational pull holds the planets in their orbits with varying escape velocities (the speed required to break the gravitational pull of a celestial body and leave orbit). Source of figure: www.Wikipedia.org.
