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Inner Planets
The eight planets in our solar system are divided into two groups: inner planets
and outer planets. The inner planets are closest to the sun. They are Mercury, Venus,
Earth and Mars. These planets are also called the terrestrial planets because they are
most similar to Earth.
Mercury is a small planet which is the closest to the Sun. Since it is between the
Sun and Earth, it is often hidden in the Sun’s glare. The Sun appears nine times larger on
Mercury than on Earth. The sun covers this planet in deadly radiation. Mercury is a ball
of rock that has craters, hills, plains and mountains. The days and nights on Mercury are
long—the time between one sunrise and the next is 180 Earth days. Mercury is the speed
demon of the Solar System, however, because it takes only 88 days to orbit around the
Venus is second from the Sun and has an orbit twice as big as Mercury. Venus is
sometimes called the morning or evening star because it appears just after sunset and
before sunrise. With sunlight reflecting off its dense cloud cover, Venus is brighter than
anything in the sky except for the Sun and moon. Because of its location between the
Sun and Earth, Venus goes through phases as does our moon. Venus is a hostile place.
Its atmosphere is carbon dioxide (CO2). The upper clouds are poisonous sulfuric acid.
Its surface temperature is approximately 900 degrees. The atmosphere alone would crush
Earth, the third planet from the Sun, is the largest of the inner planets. It is the
only planet known to have liquid water and to support life. Earth’s atmosphere absorbs
and reflects the right amount of solar energy to keep the planet at the correct temperature
for living things such as humans to survive. Earth has one moon. It takes 24 hours to
rotate on its axis and 365 days to orbit the Sun.
Mars is a small rocky planet with a thin atmosphere. It is the fourth planet from
the Sun, and about half the size of Earth. A year on Mars is nearly twice as long as a year
on Earth. It takes 687 Earth days for Mars to complete one orbit around the Sun. Mars is
sometimes called the Red Planet because its soil is dark reddish brown. Mars has two
moons and the largest volcano in the solar system, names Olympus Mons. Dust storms
on Mars last for months and affect the whole planet. Space probes have found deep
valleys and sedimentary rocks, which causes them to believe that Mars may have had
flowing water in the past.