Our Solar System: Planets, Pictures and More

A solar system is the compilation of all celestial bodies, including planets, comets and satellites, orbiting around the Sun. Formerly, scientists believed our solar system contained the following nine planets (from closest to furthest from the sun):
  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
  • Pluto.
However, further research and better technologies have led scientists to now classify Pluto as a dwarf planet, reducing the number of planets in the solar system to eight. Two other dwarf planets also in our solar system are Ceres and Eris. While these three dwarf planets have four moons altogether, the other eight planets have a total of 166 moons.
 

The Structure of the Solar System

In addition to planets, the solar system also contains a number of other types of celestial bodies, including:
  • asteroids
  • comets
  • interplanetary dust and gas
  • meteoroids
  • satellites.
The sun lies at the center of the solar system, surrounded by:
 
  1. four terrestrial inner planets (i.e. Mercury, Venus, Earth and Mars)

  2. an asteroid belt

  3. four giant gaseous outer planets, also called Jovian planets (i.e. Jupiter, Saturn, Uranus and Neptune).
At the outer edge lies a second asteroid belt called the Kuiper belt. While the inner asteroid belt is composed of small rocky bodies, the Kuiper belt contains icy objects due to the low temperatures it sustains being so far from the Sun.
 
Another nuance of our solar system is that the four outer Jovian planets have rings surrounding them, of which Saturn's are the most famous. The rings are made up of dust and other particles.
 
"Space" in the Solar System
While most people consider space not occupied by planets or other objects to be merely empty, those vast spaces consist of interplanetary dust and gas. The dust is actually made up of microscopic solid particles. The gas, mostly plasma that comes from the sun, is called solar wind.

Learning About Our Solar System: History

While many young children make solar system models each year in science class, they do not always learn about the history of solar system exploration.
 
One of the first men to hypothesize that the sun lies at the center of the universe was Nicolaus Copernicus. However, the most significant advances in our knowledge of the solar system came in the 17th century with scientists Galileo Galilei, Johannes Kepler and Isaac Newton. The discoveries of these three men finally convinced the world to accept that the Earth orbited the sun and not vice versa, as many had previously believed.
 
Galileo observed the stars with a telescope and began to explore objects too distant to be seen with the naked eye. He first discovered:
  • four satellites (a.k.a. moons) orbiting Jupiter
  • sunspots marking the sun
  • the craters in the moon.
In 1705, Edmond Halley first discovered a comet (named Halley's Comet after him) that appeared regularly every 75 to 76 years. This was the first time anyone speculated there were objects other than planets circling the sun. As telescopes became more powerful, astronomers continued to make new discoveries.
 
In1856, Father Angelo Secchi used a newly invented spectroscope to compare the spectral signature of the sun with other stars. In simpler terms, he looked at various bodies in space with a spectrometer, an instrument that measures properties of light in a certain part of the electromagnetic spectrum to measure a light's intensity. Using a spectrometer, Secchi discovered that the Sun was a star, not a planet as was previously thought. However, it took 140 years to prove this.

Pictures of the Solar System

Robotic spacecraft have accelerated space discoveries far more than telescopes have. Unmanned missions have been able to visit all of the planets, to some degree, and take close-up photographs. Landers have even been able to perform tests on the soils and atmospheres of some planets.
 
In 1957, man sent the first object into space, the Soviet satellite Sputnik I. It orbited the Earth for over a year. The first American probe, Explorer 6, was launched in 1959 and provided the first pictures of Earth.
 
Astronomers now have the technology to take pictures of both the solar system and surrounding galaxies and stars millions of light years away.

Continued Advancement

As technology continues to advance and NASA sends more missions into space, we'll continue to learn even more about our solar system. Currently, NASA has two missions to Venus planned, one for 2015 and one for 2025. Also, a ship, launched in January 2006, is now on its way to the Kuiper Belt. In 2030, NASA plans to enact a mission to Neptune.
 
The missions will search for evidence of life on other planets (or celestial bodies), seek to understand the overall history of the Solar System and perhaps even find other resources that can help human beings here on Earth.
 
Resources
 
Hamilton, Calvin J. (n.d.). The Solar System. Retrieved January 21, 2008, from the Solar Views Web site: http://www.solarviews.com/eng/solarsys.htm.
 
National Aeronautics and Space Administration (n.d.). Solar System Exploration. Retrieved January 21, 2008, from the NASA Web site: http://solarsystem.nasa.gov/index.cfm.