Source: NASA
Source: NASA

Non-Planetary Bodies
Our Solar System is a unique place filled with planets and small planetary bodies, such as asteroids, comets, dwarf planets, and meteoroids, that orbit the Sun. These small planetary bodies likely had the same origin as the planets, but never fully developed into planets. Therefore, it is very important to study non-planetary bodies, as they can lead to information regarding the formation of our Solar System. Astronomers believe that during the planetary formation, asteroids stuck together through accretion and were eventually able to become the Terrestrial Planets: Mercury, Venus, Earth, and Mars. Comets did the same and created the Jovian Planets: Jupiter, Saturn, Uranus, and Neptune. This all occurred during the Period of Bombardment, in which the universe was cluttered with millions of non-planetary bodies that were smashing into the planets causing them to grow. Once the planets we see now formed, their gravitational forces threw the left over asteroids, comets, and meteoroids into orbits throughout the Solar System. However, occasionally these bodies impacted planets after the Period of Bombardment and left significant craters on the surfaces of all the planets. These craters, however, are only visible on the smaller planets such as Mars and Mercury1.

The classification system of celestial bodies in our solar system is complex and as more information is discovered it is becoming more dynamic and all-encompassing. The complex classification system reflects our growing understanding of our universe and the variety of objects. In 2006, the International Astronomical Union defined the characteristics that determine a planet. Along with this definition, a new class of celestial objects was born known as Dwarf Planets.

Dwarf Planets
An artist's concept showing the size of the best known dwarf planets compared to Earth and its moon (top). Eris is left center; Ceres is the small body to its right and Pluto and its moon Charon are at the bottom. Source: NASA 2011

A dwarf planet is an object that orbits the Sun and is massive enough for its gravity to have made it nearly round in shape, but that does not qualify as an official planet because it has not cleared its orbital neighborhood.10 The dwarf planets of our solar system currently include the asteroid Ceres and the Kuiper belt objects Pluto, Eris, Haumea and Makemake. 9

Recently, dwarf planets have been a hot topic in the news and the world of astronomy because they are the newest born class of celestial objects. The controversy stems from Pluto's demotion from a planet to a "dwarf planet" by the IAU in 2006. Many members of the public found it hard reconciling the new view of our solar system with eight dominant planets and many dwarf planets. 11 Planets and dwarf planets are two distinct classes of celestial objects; dwarf planets are not a subclass of planets.

Asterdoids are shown as different shapes and sizes. (4)

Asteroids were first discovered in 1801 by Giuseppe Piazzi, who, at the time, actually thought the asteroid was a new planet. This early discovered asteroid was named Ceres. Asteroids are metallic, rocky bodies without atmospheres that orbit the sun, but are too small to be classified as planets. During planetary formation, Asteroids came together and formed the Terrestrial Planets: Mercury, Venus, Earth, and Mars. Known as "minor planets", tens of thousands of asteroids congregate in the so-called main asteroid belt, which is located between the orbits of Mars and Jupiter. However, asteroids are not only located in the Asteroid Belt, but they can also be located throughout most of the universe. For instance, a rather large asteroid actually just came within a couple hundred thousand miles of Earth's atmosphere. Asteroids are very large and can have diameters that are miles long. (3)(4)


Comets are similar to Asteroids in that they are undeveloped planetesimals. Comets, however, are very distinct from Asteroids because they are what formed the Jovian Planets: Jupiter, Saturn, Uranus, and Neptune. Comets are objects which formed in the outer solar system and orbit the Sun in the Kuiper Belt and Oort Cloud, beyond the orbit of Neptune, the farthest planet. Comets are basically chunks of ice mixed with rocky dust and some more complex chemicals that formed beyond the frost line. They consist of a nucleus, a coma, and two tails, though the tails only can be seen when orbiting near the Sun.

Any icy leftover planetesimal orbiting the Sun is considered a comet, regardless of its size, whether it has a tail, or where it resides or comes from. The most famous comet is Halley's Comet. It is one of the most interesting as well, since it is the only periodical comet that can become a bright naked-eye object6.

Meteor Shower Images | International Meteor Organization." International Meteor Organization | International Collaboration in Meteor Science.

Simply put, Meteors are pieces of comets. When the comet passes by the Sun during its orbit, it melts and leaves behind a dust trail of particles that eventually fill the Comet's orbit. This particles are called meteoroids. When the Earth passes through the orbit a specific comet, these particles enter our atmosphere and burst into fire, at which point most disintegrate, causing a Meteor Shower. These are not rare in the least. In fact, because of the predictable and known orbits of comets, specific meteor showers from the meteoroids of specific comets occur at the same time every year. It is important to note that right after the Comet has passed by the sun and left new material in its orbit, this causes a Meteor Storm when Earth passes through the orbit. Meteor Storms only happen every once in a while as the orbit of comets are often times hundreds of years, however. Meteor Showers are important because they allow humans to experience outer space because they bring fragments of celestial bodies into our world7.

Related Viewings

Non-planetary bodies are often overlooked by many because they are not one of the elite eight. However, they are vitally important to our understanding of the solar system and the even the entirety of the universe because they are what make up the eight planet, including our own. For further information on non-planetary bodies, follow the links throughout the article above the related links listed below.

1. The following video details the possibilities of comets and asteroids hitting the Earth:

2. To view another video on the different areas of the Solar System, follow this link.

Related Readings:
1. Follow this link, provided by NASA, to get a better, interactive, and hands-on idea about how asteroids, comets, and near-Earth objects move within our solar system. 8
2. Research on small planetary bodies by Nasa

List of References:
1. Bennett, Jeffrey O. The Cosmic Perspective. Boston: Addison-Wesley, 2010. Print.
2. Bennett, Jeffrey O. The Cosmic Perspective. Boston: Addison-Wesley, 2010. Print.
3. "Asteroids." Welcome to the NSSDC! NASA / Near Press Kit. Web. 29 Nov. 2011. <>.
4. "Asteroids L Asteroid Facts, Pictures and Information." The Nine Planets Solar System Tour. Nine Planets. Web. 29 Nov. 2011. <>.
5. "Comets and Asteroids." Indiana University. Web. 02 Dec. 2011. <>.
6.Bennett, Jeffrey O. The Cosmic Perspective. Boston: Addison-Wesley, 2010. Print.
7."Meteor Showers." American Meteor Society. Web. <>.
8. Greicius, Tony. "NASA - Asteroid and Comet Watch." NASA - Home. NASA / Near Press Kit, 7 Nov. 2011. Web. 29 Nov. 2011.
9. International Astronomical Union. Web. 1 Dec. 2011. <>.
10. Brown, Mike. Mike Brown's Planets. N.p., 2011. Web. 1 Dec. 2011. <>.
11. Jaggard, Victoria. "Should Pluto be a Planet? New Finds Drive Debate". National Geographic. National Geographic Society. Nov. 2011. <>.