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Sun
The Sun is a star, a hot ball of glowing gases at
the heart of our solar system. Its influence
extends far beyond the orbits of distant Neptune
and Pluto. Without the Sun's intense energy and
heat, there would be no life on Earth. And though
it is special to us, there are billions of stars
like our Sun scattered across the Milky Way
galaxy.
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Mercury
Sun-scorched Mercury is only slightly larger than
Earth's Moon. Like the Moon, Mercury has very
little atmosphere to stop impacts and it is
covered with craters. Mercury's dayside is super
heated by the Sun, but at night temperatures drop
hundreds of degrees below freezing. Ice may even
exist in craters. Mercury's egg-shaped orbit takes
it around the Sun every 88 days.
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Venus
Venus is a dim world of intense heat and volcanic
activity. Similar in structure and size to Earth,
Venus' thick, toxic atmosphere traps heat in a
runaway 'greenhouse effect.' The scorched world
has temperatures hot enough to melt lead. Glimpses
below the clouds reveal volcanoes and deformed
mountains. Venus spins slowly in the opposite
direction of most planets.
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Earth
Earth is an ocean planet. Our home world's
abundance of water - and life - makes it unique in
our solar system. Other planets, plus a few moons,
have ice, atmospheres, seasons and even weather,
but only on Earth does the whole complicated mix
come together in a way that encourages life - and
lots of it.
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Mars
Though details of Mars' surface are difficult to
see from Earth, telescope observations show
seasonally changing features and white patches at
the poles. For decades, people speculated that
bright and dark areas on Mars were patches of
vegetation, that Mars could be a likely place for
life-forms, and that water might exist in the
polar caps. When the Mariner 4 spacecraft flew by
Mars in 1965, many were shocked to see photographs
of a bleak, cratered surface. Mars seemed to be a
dead planet. Later missions, however, have shown
that Mars is a complex member of the solar system
and holds many mysteries yet to be solved.
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Jupiter
The most massive planet in our solar system, with
four large moons and many smaller moons, Jupiter
forms a kind of miniature solar system. Jupiter
resembles a star in composition. In fact, if it
had been about 80 times more massive, it would
have become a star rather than a planet.
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Saturn
Saturn was the most distant of the five planets
known to the ancients. Like Jupiter, Saturn is
made mostly of hydrogen and helium. Its volume is
755 times greater than that of Earth. Winds in the
upper atmosphere reach 500 meters (1,600 feet) per
second in the equatorial region. These super-fast
winds, combined with heat rising from within the
planet's interior, cause the yellow and gold bands
visible in the atmosphere.
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Uranus
The first planet found with the aid of a telescope,
Uranus was discovered in 1781 by astronomer
William Herschel. The seventh planet from the Sun
is so distant that it takes 84 years to complete
one orbit.
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Neptune
Nearly 4.5 billion kilometers (2.8 billion miles)
from the Sun, Neptune orbits the Sun once every
165 years. It is invisible to the naked eye
because of its extreme distance from Earth.
Interestingly, the unusual elliptical orbit of the
dwarf planet Pluto brings Pluto inside Neptune's
orbit for a 20-year period out of every 248 Earth
years
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Pluto
Tiny, cold and incredibly distant, Pluto was
discovered in 1930 and long considered to be the
ninth planet. But after the discoveries of similar
intriguing worlds even farther out, Pluto was
reclassified as a dwarf planet. This new class of
worlds may offer some of the best evidence of the
origins of our solar system.