Exam 8: Comparative Planetology II: the Origin of Our Solar System

Suppose the ratio of radiogenic ⁴⁰K to nonradiogenic ³⁹K was 1:10 at the time a rock was formed, and that at that time also the ratio between radiogenic ⁴⁰Ar to ³⁹K was 1:20. Now, when the rock is analyzed, it is found that the ratios are ⁴⁰K/³⁹K = 1:20 and ⁴⁰Ar/³⁹K = 1:10. How old is the rock (in billions of years)?

In a rotating physical system (e.g., a star formation region or a skater), what happens to the rotation rate (or angular speed) when the mass of the system condenses toward the center of rotation?

As the early Sun got smaller in a Kelvin-Helmholtz contraction, its interior became hotter and gained thermal energy. What was the source of this energy?

An early theory of solar system formation was the tidal hypothesis-the idea that a star passed close enough to the Sun to draw out a long filament of material that then condensed to form the planets and other solar system bodies. Why was this theory discredited?

Which substances form ice in the outer solar system?

How has the present mix of chemical elements in the universe been produced?

Of all the stars with metal abundances like the Sun surveyed so far by the radial velocity method, about how many have planets in orbit around them?

How do we explain the relatively low mass of Mars, which is much smaller than Earth or Venus?

Which of these chemical elements is relatively rare in the universe?

The ages of meteorites have been found through radioactive dating. One major difficulty with this technique is that:

In order to employ the radioactive age-dating technique on a sample of rock, it is necessary to know all of these except one. Which is the exception?

Our solar system seems to have formed about how long ago?

Which of the these types of material has the highest condensation temperature in the planetary system?

Each of these is a technique used to discover exoplanets except one. What is the exception?

It is found by the radioactive age-dating technique that only one-quarter of the original sample of a radiogenic element remains, so the time is calculated to be two half-lives. What does this time represent?

In the early solar nebula, iron sulfide condensed into solid form at a temperature of about 750 K. What is the smallest distance from the Sun at which this would have happened? (See Figure 8-10 of Universe, 11th ed.) ​ ​

When dealing with radioactive decay of materials, we often read about the age of a particular rock. What is meant by the age of a rock?

Table 8-1 of Universe, 11th ed (in the text). lists three general properties of the solar system. These deal with the size and composition of terrestrial planets versus jovian planets, directions and orientations of planetary orbits, and sizes of terrestrial planetary orbits versus jovian planetary orbits. Which planets do not fit into this general scheme?

Suppose the ratio of radiogenic ²³⁸U to nonradiogenic ²⁰⁴Pb was 4:100 at the time a rock was formed, and also that at that time, the ratio of radiogenic ²⁰⁶Pb to ²⁰⁴Pb was 1:100. Now, when the rock is analyzed, it is found that the ratios are ²³⁸U/²⁰⁴Pb = 1:100 and ²⁰⁶Pb/²⁰⁴Pb = 4:100. How old is the rock (in billions of years)?

The most common ices in the early solar nebula were: