5.1   In a poetic sense, planets are sometimes referred to as "children of the Sun."  A more accurate description, though, would be "siblings of the Sun."  Explain.

The planets were "born" with the Sun - they didn't come from it.

5.6   Nearly all of the planets astronomers have found orbiting other stars have been giant planets with masses more like that of Jupiter than Earth, and with orbits located very close to their parent stars.  Does this mean that our Solar System is unusual?  Explain.

The kinds of planetary systems that have been found so far are the kind we are sensitive to - we wouldn't be able to identify a planet like Earth like Earth.   To find a planet like Jupiter at Jupiter's distance would take about as long as people have been looking, so it isn't so odd one hasn't been found yet.

5.7   Why do we find rocky material everywhere in the Solar System, but large amounts of volatile material only in the outer regions?  Would you expect the same to be true of other solar systems?  Explain.

Because it was cooler during the early life of the Solar System and the planets could hold on to solid volatile material when the warmer inner planets couldn't hold on to gaseous volatiles.

Yes, we would expect the same to be true of other planetary systems.  Unless a large outer planet migrated in toward its star well after formation, when it was cooler.

5.9   Use the information on the planets given in the Appendices to answer the following:
        a.  What is the total mass of all th eplanets in our Solar System expressed in Earth masses?
        b.  What fraction of this total planetary mass does Jupiter represent?
        c.  What fraction does Earth represent?

a.  The total mass is 0.055 + 0.815 + 1.00 + 0.107 + 317.83 + 95.16 + 17.15 + 0.0021 = 446.659 Earth masses

b.  Jupiter's mass represents  317.83/446.659 = 71% of the total.

c.  Earth's mass represents    1/446.659 = 0.224% of the total