Earth And Space
In Space: Despite its own special conditions,the Earth is in some ways
similar
to the other inner planets the group of planets nearer to the sun.Of
these
planets,Mercury is the closest to the sun;Venus is second;the Earth is
third
;and Mars is fourth.All of these planets, including the Earth,are
basically
balls of rock.Mercury is the smallest in size. Its diameter is
about two thirds
the greatest width of the Atlantic Ocean. Mars is larger
than Mercury,but its
diameter is only a little more than half that of the
Earth.Venus,with a diameter
of roughly 7,600 miles (12,000 kms),is almost as
large as the Earth. Four of the
five outer planets are much bigger than any
of the inner Planets.The largest,
Jupiter , has a diameter more than 11
times as great as that of the Earth.These
four outer planets are also much
less dense than the inner planets. The exact
size or mass of Pluto, the most
distant planet ,is not known. Its composition is
also a mystery.All that is
known for sure about Pluto is its orbit.Pluto's
average distance from the sun
is almost 40 times that of the
Earth.