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Pluto discovered in 1930. It is small and frozen. It has one satellite. It turns around the sun every 249 years. Pluto is smaller than 7 of the moons in the Solar System. Because it is so small many scientists don't consider it a planet at all.
Source:http://www.wsc.ma.edu/personalpages/draker/edcom/final/webprojects/fa06/ultra/u8.html
Because this planet lies so close to the Sun, and as a result somewhat near to the Earth, it is visible to observers on Earth in the night time sky.
Source:http://en.wikiversity.org/wiki/Solar_System/Earth/Solar_System_overview/Mercury
Source: http://newswiseblog.blogspot.com/2009_05_01_archive.html
The earth is the third planet away from the sun, and it is the eight largest planets. It is the only place in the Universe where life exists, home to millions of species, including humans. It has water in abundance. It turns around the sun every 365.25 days.
It is sometimes referred to as the Blue Planet or the World.