Lesson 13.4: Science Connection

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Postcards from Pluto?

Scientists know quite a bit about most of the planets in the solar system. And then there is Pluto.

Pluto is the smallest planet and, most of the time, it is the farthest planet from the Sun. Scientists also know that Pluto is very cold and that it has just one moon. But that is about all they know.

Even powerful telescopes don't reveal much about Pluto except that it is a barely visible point of light that looks much like a star. Pluto remains the only planet not yet visited by an Earth-launched spacecraft.

Scientists at the National Aeronautics and Space Administration (NASA) want to change that. They plan to send a robotic probe 2.9 billion miles across the solar system to take pictures of Pluto in order to learn as much as possible about that distant planet.

For this $546 million mission, NASA will build a spacecraft called New Horizons. NASA hopes to launch the robotic probe in January 2006. But, even if the launch goes smoothly and according to plan, New Horizons won't reach Pluto until 2016.

Timing Is Everything

Pluto takes almost 248 Earth-years to orbit the sun. If the New Horizons mission is delayed even by one year, scientists say, their next chance to gather information about Pluto might not come until after 2200! Why is that?

As Pluto moves farther away from the Sun, the planet's atmosphere freezes. Its temperature drops below -400 degrees Fahrenheit! Frozen solid at temperatures that low, scientists say there might not be much to see on Pluto until it returns to a point in its orbit where the Sun warms it.

Timing Beyond Pluto

In 2007, a year after its scheduled launch, New Horizons is expected to pass close to Jupiter. Scientists want to use Jupiter's gravity like a slingshot to propel the spacecraft onward to Pluto.

In July 2016, astronomers hope to get their first close-up of Pluto as New Horizons whips by the icy planet at 27,290 miles per hour!

After snapping pictures of Pluto during a six-month period, New Horizons would travel for ten more years deep into the Kuiper Belt, a ring of icy rocks beyond Neptune's orbit. Many scientists believe the Kuiper Belt is where many comets originate. Comets are made up of big chunks of ice, rock, and gases. NASA calls comets “dirty ice leftovers from the formation of our solar system.”

Some astronomers believe Pluto should be counted as a Kuiper Belt object rather than as the ninth planet. New Horizons could settle that issue once and for all. Then again, if the mission is scrapped for any reason, Pluto—and astronomers—will be left out in the cold.

Timing Late Arrival

Astronomers once believed there were only eight planets in the solar system. Then, in 1930, Clyde W. Tombaugh looked at some photographic plates of the night sky and identified a faint point of light he called Planet X. It later was named Pluto for the Roman god of the underworld.

Pluto has a diameter of about 1,400 miles, smaller than that of Earth's moon. Despite its small size, many scientists say Pluto meets the definition of a planet. This is in part because it orbits the sun. Another astronomer, James W. Christy, discovered Pluto's moon in 1978. He named the moon Charon, after a character in Greek mythology.

Word Wise

Machine that does some things that people do: At the tollbooth, a robotic arm reached out and took our ticket.

Tool used to examine something carefully: Dentists use probes to check people's teeth and gums.

Move around in a set path around an object: It takes Earth 365 1/4 days to completely orbit the Sun.

Air that surrounds a planet or a moon: Pluto's atmosphere is made up of nitrogen and methane gas.

Force that pulls all things downward toward a large body, such as a planet: Because Pluto's gravity is weaker than Earth's, on Pluto you would weigh 1/15 of what you weigh on Earth.

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You know that nouns and verbs are two parts of speech. A noun is a word used to name a person, a place, or a thing. A verb is a word that expresses action or the state of being.

Look back at the list of Word Wise words. One of the words is used as a noun but also has meaning as a verb. Another word is used as a verb but also has meaning as a noun.

  1. Decide which two vocabulary words can be both a noun and a verb.
  2. For each word, make up two sentences—one sentence using the word as a noun, and another using it as a verb.
Can you think of any other words that can be used as a verb and as a noun?

Data Hunt

The distance that light can travel in one year's time is called a light year. One light year is equal to 9 trillion, 500 billion kilometers!

You can write this very large number as 9,500,000,000,000 km. You can also write it in scientific notation, like this:

9.5 x 1012

The Hubble Space Telescope took a picture of Pluto and its moon, Charon, in 1994. At that time, Pluto was 4 billion, 400 million kilometers from Earth.

  • Write 4,400,000,000 km in scientific notation.