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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.