The Solar System

CHAPTER 19 | THE ORIGIN OF THE SOLAR SYSTEM 423

Learning to Look

1. What do you see in the image at the
   right that indicates this planet formed
   far from the sun?


2. Why do astronomers conclude that the
   surface of Mercury, shown at right, is
   old? When did the majority of those
   craters form?


3. In the mineral specimen represented to
   the right, radioactive atoms (red) have
   decayed to form daughter atoms (blue).
   How old is this specimen in half-lives?
   (See Figure 19-7).


4. What composition might you expect for a planet that formed in a
   region of the solar nebula where the temperature was about 100 K?


5. Suppose that Earth grew to its present size in 1 million years through
   the accretion of particles averaging 100 grams each. On the average,
   how many particles did Earth capture per second? (Hint: See Appendix
   A to fi nd Earth’s mass.)


6. If you stood on Earth during its formation, as described in Problem 7,
   and watched a region covering 100 m^2 , how many impacts would you
   expect to see in an hour? (Hint: Assume that Earth had its present
   radius. The surface area of a sphere is 4πr^2 .)


7. The velocity of the solar wind is roughly 400 km/s. How long does it
   take to travel from the sun to Earth?

NASA

NASA