Like many of you I have been pressed into teaching astronomy without having
been formally taught in this area. However, I do have a Ph.D. in geology
so I think I know a little bit about at least one planet. Two questions at
the end of the Chaisson/McMillan chapter on the earth suggest possible
misconceptions and since this list seems to thrive on such issues I though
I would mention them. I don't have an answer key (is there one?) so I'm not
sure what the authors have in mind. I'm only guessing. Here goes.
P 169 Review & Discussion
#5. How would our knowledge of Earth's interior change if our planet were
geologically dead, like the moon? I imagine that the idea is that we would
not know as much because without earthquakes we would be short on seismic
sources. However, man made sources are generally preferred to earth quakes.
One never knows exactly when or where an earthquake took place. For info
on the deep interior we clearly need a big source, but nuclear weapons tests
have proved to be ideal.
#10. How did radioactive decay heat the Earth early in its history? When did
this heating end? Perhaps this is supposed to be a trick question?
Considering the fact that the junk that floated around in space for an unknown
length of time before we claimed it and that there are many isotopes with
half lives on the order of billions of years, this question seems pecular.
There have been many competing models proposed for the thermal history of the
earth and as far as I know the jury is still out on most of them.
#14. If the Moon had oceans like the Earth's, what would the tidal effect be
like there? How many high and low tides are there during a "day?" How would
the variations in height compare to those on the Earth? I think Jim Green
wants to answer this one.
I do think these guys do a nice job on Mercury's 3:2 spin-orbit resonance
or "tidal lock" to the sun. (three rotations for 2 revolutions)