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.