THE
BEGINNING
BIRTH OF THE SOLAR SYSTEM
What do we mean by the solar system?
Our solar system--and presumably others--consists of a star， plan
satellites， comets， asteroids， meteoroids， and interplanetary dust
gas. Our solar system includes the following:
Sun--The Sun is at the center of our solar system， and is an average
when compared with other stars in the universe. It is classed as a typ
G2-class star， represents about 99.86 percent of the mass of the s(
system， and is about 864，000 miles (1，390，180 kilometers) in diame
or about 109 Earth diameters across. It is thought that the Sun arri
at its present brightness about 800 million years ago， and will proba
burn for another seven billion years.
Nine known planets--From the Sun outward， the planets are M
cury， Venus， Earth， Mars (the inner， or terrestrial， planets); Jupi
Saturn， Uranus， Neptune (the outer， or gaseous， planets， or
giants); and Pluto (which is more similar in characteristics to the t
restrial planets).
Moons--More than 64 moons (satellites) circle the various planets
addition， a moon has also been found around the small minor pla
(asteroid) Ida， and some scientists believe such tiny moons arou
asteroids may be common. Saturn has the most known moons (m
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