Homework 3 Answers

1. Chapter 9, problems 1—4 (Page 257)
   1. This is not reasonable. Mercury has little atmosphere to create sand dune like features.
   2. This isn't totally unreasonable. Venus is volcanically active and a new volcano isn't out of the question.
   3. This is unreasonable. Venus has lacked liquid water needed to make sedimentary rocks for the last billion years. Since most of the surface (if not all of it) is younger than a billion years old, no sedimentary rocks should be left, even if they ever formed at all.
   4. This is also unreasonable. Erosion would have destroyed the craters long ago and resurfacing due to tectonics and volcanism would have replaced the surface.
2. Chapter 9, problem 8 (Page 257)
   
   1. I'd send a magnetic field measuring device along. If the planet has a metallic core exists and the planet is v still warm inside (it is rotating fast enough), it should have a magnetic field. You could also measure the density of the overall planet. A metallic core would make the planet much denser than otherwise. You can measure this by finding the mass of the planet via Newton's Version of Kepler's Third Law and knowing the radius.
   2. If the planet had few radioactive element, the surface would probably be geoloically dead by now, with no volcanism or tectonics. If you find evidence of recent volcanic or tectonic activity, it's a good guess that the planet is radioactive inside.
   3. To see if there is an atmosphere, I'd look for erosional features. Both water and wind erosion require an atmosphere to happen, so lack of those kinds of features would indicate that an atmosphere probably isn't present. (It still could be, like on Venus. But Venus is a pathelogical case.)
3. Chapter 6, problems 1—2 (Page 169)
   1. This doesn't make sense (mostly). A blue sweatshirt should reflect mainly just the blue light. (In reality, it would probably reflect a bit of the other colors. If this is explained clearly as your reasoning, credit will be give.)
   2. This isn't sensible. All light travels at the same speed through space.
4. Chapter 6, problem 5 (Page 169)
   1. The surface composition can be guessed at based on which colors the object reflects back out. In figure 6.14, the reflect sunlight curve (left hump) shows that much of the blue light is being absorbed. This tells us that the surface might have rusted iron, for example.
   2. We can derive surface temperature by using the laws of blackbodies. Take the blackbody emission hump and find the peak. This tells us the temperature.
   3. If the object is a thin cloud, we'll see emission lines or bands (depending whether it's made of atoms or molecules). Otherwise, we see a continuous spectrum
   4. If the object has a very hot upper atmosphere, there should be UV emsission lines from the hot atoms emitting high-energy photons.
   5. To get the obejct's speed, we can measure how shifted certain emission lines are from where we find them in the lab. The shift is due to the speed at which is approaches or receeds from us.
   6. To get the rotation rate, we should see how broadened the emission lines are. This is just a Doppler shift (as above), but where part
   of the object is moving towards us and part is moving away.
5. Chapter 6, problem 6 (Page 169)
   

   The spectrum should show some visible light: blue is clearly visible. The light must be reflected, since planets are too cool to emit much visible light. (The Sun, being many times hotter, emits a lot of it.) I would expect to find very little red light in the spectrum, however, since the planet seems to be reflecting mainly the blue.