Unit 4: Science Connection

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Is Pluto a Planet?

Most people say our solar system is made up of nine planets. But some scientists think that number should be eight. They say that Pluto is not a planet.

Because Pluto is so small, some scientists say it is an asteroid. An asteroid is a rocky object that moves in the solar system. Scientists know that Pluto is made up of rock and ice.

Pluto Facts
Pluto was discovered in 1930.
Pluto is the smallest planet. It is even smaller than Earth's moon!
Pluto has one moon. It is named Charon.
The temperature on Pluto is very cold — much colder than Earth.
A day on Pluto is 153 hours long!

Word Wise

solar system:
The sun and the nine planets, including Earth: Jupiter is one of the planets in the solar system.

planet:
A large object that moves around a star, such as the sun: We live on the planet Earth.

scientist:
Someone who is an expert in a science.

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Activity

Word Wise Quiz
Choose the best word to complete each sentence in the Word Wise Quiz.

Data Hunt

Compare Pluto to Earth. What facts do you know about the planet Earth? Can you answer these questions?

  1. How many hours are in a day on Earth?
  2. How many hours are in a day on Pluto?
  3. How many moons does Earth have? How about Pluto?
  4. Is Earth smaller or bigger than Pluto?

Write your answers on a sheet of paper. How does Earth compare to Pluto?