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Introduction to Solar
System
Solar System, the Sun and the celestial
bodies orbiting the Sun, including the nine planets and their satellites;
the asteroids and comets; and interplanetary dust and gas. The term may
also refer to a group of celestial bodies orbiting another star (see
Extrasolar Planets). In this article, solar system refers to the system
that includes Earth and the Sun. The dimensions of the solar system are
specified in terms of the mean distance from Earth to the Sun...more
The Sun
The Sun�s gravitational pull holds the solar system together. The planets,
asteroids, comets, and dust that make up our solar system are strongly
attracted to the Sun�s huge mass. This gravitational attraction keeps
these bodies in orbit around the Sun. The Sun also influences the solar
system with its diffuse outer atmosphere, which expands outward in all
directions. This expanding atmosphere fills the solar system with a
constant flow of tiny, fast, electrically charged particles...more
The
Major Planets
The most detailed information available
about Mars has come from unpiloted spacecraft sent to the planet by the
United States between 1964 and 1976. From this data, scientists have
determined that the planet�s atmosphere consists primarily of carbon
dioxide, with small amounts of nitrogen, oxygen, water vapor, and other
gases...more
Other Orbiting Bodies
The asteroids are small rocky bodies that
move in orbits primarily between the orbits of Mars and Jupiter. Numbering
in the thousands, asteroids range in size from Ceres, which has a diameter
of 1,003 km (623 mi), to microscopic grains. Some asteroids are perturbed,
or pulled by forces other than their attraction to the Sun, into eccentric
orbits that can bring them closer to the Sun. If the orbits of such bodies
intersect that of Earth, they are called meteoroids...more
Movements of Planets
If one could look down on the solar system
from far above the North Pole of Earth, the planets would appear to move
around the Sun in a counterclockwise direction. All of the planets except
Venus and Uranus rotate on their axes in this same direction. The entire
system is remarkably flat�only Mercury and Pluto have obviously inclined
orbits. Pluto�s orbit is so elliptical that it is sometimes closer than
Neptune to the Sun...more
Theories of Origin
Current theories connect the formation of
the solar system with the formation of the Sun itself, about 4.7 billion
years ago. The fragmentation and gravitational collapse of an interstellar
cloud of gas and dust, triggered perhaps by nearby supernova explosions,
may have led to the formation of a primordial solar nebula. The Sun would
then form in the densest, central region. It is so hot close to the Sun
that even silicates, which are relatively dense, have difficulty forming
there...more |
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