The Solar System

492 PART 4^ |^ THE SOLAR SYSTEM

4. What evidence shows that Venus has been resurfaced within the last
   billion years?


5. Why doesn’t Mars have mountain ranges like those on Earth? Why
   doesn’t Earth have large volcanoes like those on Mars?


6. What were the canals on Mars? How do they differ from the outfl ow
   channels and valley networks on Mars?


7. Propose an explanation for the nearly pure carbon dioxide atmospheres
   of Venus and Mars. Why is Earth’s atmosphere different?


8. What evidence can you cite that the climate on Mars has changed?


9. How can planetary scientists estimate the ages of the outfl ow channels
   and valley networks on Mars?


10. Why are Phobos and Deimos nonspherical? Why is Earth’s moon much
    more spherical?


11. How Do We Know? How are a weather radar map and an image of a
    mountain on Venus related?

Discussion Questions

1. From what you know of Earth, Venus, and Mars, do you expect the
   volcanoes on Venus and Mars to be active or extinct? Why?


2. If you had a time machine, plus superpowers suffi cient to modify or
   move entire planets, what would you change about Mars, as it was
   forming, to make its surface environment remain more Earth-like to the
   present day? How about Venus?


3. Can you make a hypothesis about a single event that might explain
   both Venus’s slow rotation and its geologically recent resurfacing?


4. If humans someday colonize Mars, the biggest problem may be fi nding
   water and oxygen. With plenty of solar energy beating down through
   the thin atmosphere, how might colonizers extract water and oxygen
   from the Martian environment?

Problems

1. How long would it take radio signals to travel from Earth to Venus and
   back if Venus were at its nearest point to Earth? At its farthest point
   from Earth? (Hint: The speed of light is 3.00  108 meters per second.)


2. The Pioneer Venus orbiter circled Venus with a period of 24 hours.
   What was its average distance above the surface of Venus? (Hint: See
   Chapter 5.)
   3. Calculate the velocity of Venus in its orbit around the sun. (Hint: See
   Chapter 5.)
   4. What is the maximum angular diameter of Venus as seen from Earth?
   (Hint: Use the small-angle formula, Chapter 3.)
   5. If the Magellan spacecraft transmitted radio signals down through
   the clouds on Venus and heard an echo from a certain spot 0.000133
   second before the main echo, how high is the spot above the average
   surface of Venus? (Hint: The speed of light is 3.00  108 meters per
   second.)
   6. The smallest feature visible through an Earth-based telescope has an
   angular diameter of about 1 arc second. If a canal on Mars was just
   visible when Mars was at its closest to Earth, how wide was the canal?
   (Hint: Use the small-angle formula, Chapter 3.)
   7. What is the maximum angular diameter of Phobos as seen from Earth?
   What surface features should you expect to see from Earth? From
   the surface of Mars? (Hints: Use the small-angle formula, Chapter 3,
   and use information in the Appendix tables to derive the distances
   between the objects in question.)
   8. What is the maximum angular diameter of Deimos as seen from the
   surface of Mars? (Hints: Use the small-angle formula, Chapter 3,
   and use information in the Appendix tables to derive the distances
   between the objects in question.)
   9. Deimos is about 12 km in diameter and has a density of 2 g/cm^3. What
   is its mass? (Hint: The volume of a sphere is 4 __ 3 πr^3 .)

Learning to Look

1. Volcano Sif Mons on Venus is shown
   in this radar image. What kind of
   volcano is it, and why is it orange
   in this image? What color would the
   rock be if you could see it with your
   own eyes?


2. Olympus Mons on Mars is a very large
   volcano. In this image you can see
   multiple caldera at the top. What do
   those caldera and the immense size
   of the volcano indicate about the
   geology of Mars?

NASA

NASA