Earth Science Lesson 1
The Solar System

Pre-Test
Q&A	The Universe

Instruction 1-7

The Solar Nebula/Earth's Formation from the Nebula | Cloud of Dust Theory | Formation and Origin of the Moon | Early Earth | The Sun | Effects of Asteroid Impacts in Shaping the Surface of Planets | Evidence for the Existence of Planets Orbiting Other Stars | Summary

Evidence for the Existence of Planets Orbiting Other Stars
http://spiff.rit.edu/classes/phys230/lectures/planets/planets.html

Are we alone? Or is there life somewhere else in the universe? We don’t know. So far as we can tell, there doesn’t seem to be life on any of the other planets in our Solar System. Those planets, as you remember, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, Uranus and Pluto.

Mercury, Venus, Earth and Mars are called terrestrial planets. This means they are composed mainly of rock and metal.

Jupiter, Saturn, Uranus and Neptune are called gas giants. They’re made mostly of hydrogen and helium.

Here’s how far each planet is from the Sun. The distances are very great. Neptune, for example, is 30 times farther from the Sun than the Earth is.

To learn more about these planets, click http://www.seds.org/nineplanets/nineplanets/nineplanets.html

But are there other planets revolving around other suns in other parts of the universe? Yes.

Astronomers began to suspect this as early as 1916, when they observed a star called “Barnard’s Star.” This star had a very peculiar wobble. This wobble suggested that it was being pulled out of its orbit by the gravity from an object revolving around it. But we didn’t know for sure until November 16, 1999. That’s when photographic evidence first proved the existence of an “extrasolar” planet. This means a planet revolving around a star outside our Solar System. 

How do scientists look for these planets? By checking out their gravitational effect on stars. A large planet orbiting a star will cause it to wobble.

To see what we mean, try this. Spin around in a circle. Then ask somebody to grab your hand. That pull on your arm will make you spin off center, or wobble.

This wobble turns up as a particular kind of smudge on the photograph of a star. And by monitoring the spectrum of the star, we can tell whether it is moving toward us or away from us. If the star’s spectrum is shifted toward the red, it is moving away from us. If it is shifted toward the blue, it is moving toward us.

When astronomers find one of these wobbling stars, they feel pretty sure they have discovered an extrasolar planet. Most of these extrasolar planets are believed to be gas giants like Jupiter, Saturn, Uranus and Neptune. They are probably several times the size of Jupiter.

Why do we think they’re that huge? Because a smaller planet would not exert enough gravitational pull on its star for us to see it or measure it. New tools such like the Hubbell Space Telescope let us see many stars that may be circled by planets. And more instruments are being developed all the time to help us see even farther out into space. Soon, we may actually be able to see closeups of extrasolar planets and measure their chemical composition. And, if we’re lucky, find out if there’s life out there after all.

To learn more about extrasolar planets, click http://www.seasky.org/cosmic/sky7a02.html

Experiments for Home and Classroom

An amazing project called "Planet Quest," sponsored by NASA, is searching for planets that orbit stars outside the Solar System. Many so-called "exoplanets" have already been found -- some 200 light years away. But do any of them qualify as "another Earth?" This 16-page Planet Quest web site explains the project and lists ways in which students can actually join in the search. This is the stuff that science fiction is made of -- but it's for real!

To take a virtual journey into the Universe -- to tour the Solar System and beyond -- students are invited to click: http://library.thinkquest.org/28327

And finally, to explore the question "Are Humans Alone in the Universe?" students can visit this web site and choose from one to four different "missions." Although designed for younger children (9th Graders), this exploration is appropriate (and exciting) for anyone who has ever wondered about life beyond Earth. Click:
http://jvsc.jst.go.jp/universe/et_e/index_e.htm 

Now let's do Practice Exercise 1-7 (top)

Summary

You have now completed Lesson 1 on the Solar System and are ready to do the Problem and Test sections.

You may wish to review any or all of the topics before answering the questions that follow. You may also wish to obtain additional material from the links below before answering the questions.

Good luck!

http://www.enchantedlearning.com/subjects/astronomy/activities/

http://geosun.sjsu.edu/paula/103/html/Earthsplace.htm

Next Page:  Problems (top)