The Solar System: Mostly Space

David Bowie: Space Oddity

(Courtesy NASA/ JPL-Caltech)

This is a mosaic of six of the planets of the Solar System. In fact, it is the only "portrait" of the Solar System we have taken from outside the Solar System. The Voyager spacecraft created this mosaic from over 60 individual pictures in June 1990 when it was about 4 billion miles from Earth. This mosaic begins to show just how tiny the Sun and the planets are compared to the amount of space in the Solar System.

The Sun, shown in the actual size it appeared to Voyager, is the bright spot in the top left hand corner. All of the planets were too far away for Voyager to resolve with the exceptions of Jupiter and Saturn. As a result, all the positions of the six planets in this mosaic are indicated by the first letter of their names. What may have been the reasons why Mercury and Mars could not be photographed?

Roll your mouse over the above image to see a picture of the golden record on-board the Voyager spacecraft. Click on the image to learn more about it.

Most of the mass in the Solar System, belongs to the Sun. The Sun makes up over 99.85% of the mass of the Solar System. The rest comes from planets and all the smaller bodies of the Solar System that we'll get to shortly. The Sun's volume is 337 quadrillion cubic miles, which is over 600 times the combined volume of all the other bodies in the Solar System. However, the Sun occupies far less than one trillionth of one percent of the total volume of the Solar System! All the other bodies in the Solar System make up far less than that, which means that the Solar System is mostly space.

It's really hard to image just how much space there is out in the Solar System. However, in 1990 it got a bit easier. It was then that the Voyager spacecraft, launched in 1977, turned back towards the Sun and made the first "portrait" of the Solar System. The planets appeared as tiny points to Voyager and were only visible after the pictures taken were magnified many times. The rest of the mosaic, except for the Sun, is just empty space.

In 2006, Voyager became the first human made object to approach the boundary of the Solar System. It is now over 10 billion miles away from the Sun, more than 100 times farther away from the Sun than Earth, or twice as far away as Pluto. No one is sure what the Voyager probe will encounter.

(Courtesy NASA/JPL-Caltech)

The drawing above shows the tht Solar System's termination shock and heliosheath.

Before we move onto the smaller things in the Solar System, let's talk about the region of the Solar System in which many of them are found. This region called theKuiper Belt is a large area that extends from the orbit of Neptune, between about 30-50 Astronomical Units (1 AU = the distance from Earth to the Sun) away. All the objects found in the Kuiper Belt are called trans-Neptunian objects, since they are past the orbit of Neptune. There is also a spherical cloud called the Oort Cloud, which is well beyond the current agreed upon boundary of the Solar System. However, the Oort Cloud is the origin of some of the strange small solar system bodies that occasionally show up close to Earth.

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Website created March 2007 by Sam Singer, last updated December 2009