Astronomy 23/223 Homework:

What's Mercury Made of?

This homework assignment is investigating Mercury using the tools of mathematics, chemistry, and spectroscopy. It requires a combination of calculation, description,internet research, and identificaiton.


1. a)

Density. Using th planet's mass and volume, calculate the density of Mercury. What is the problem with comparing this number to laboratory values for the density of materials? In otherwords, what factors other than composition are effecting the density of Mercury?

The materials on Mercury are subject to different pressures and temperatures than those in the lab. As a result, you can not compare Earth-based room temperature and pressure density measurements to those on Mercury.



Assuming that the planet is composed of both iron and rock, model the density of the planet. To do this, use

where is the volume fraction of the planet that is rock and is the volume fraction that is iron. Using the fact that both these fractions must add up to one, the density of a rock as 3.5 (g/cm3) and the density or iron as 7.9 (g/cm3), calculate the volume fractions of iron and rock. Now calculate the fraction by mass. You can do this by creating a similar total density equation or by using the information you already have.

The X values reffer to the percentage of the volume while the Y values reffer to the percentage of mass.

2. a) Composition from Spectroscopy. Explain the difference between reflectance and gamma-ray spectroscopy. How do each of them work and what information can be found from each respectively?

Search the web for information about when both techniques have been used. What information about Mercury's composition has been found from these techniques? Explain the signifance of findings at at least two different wavelengths of reflectance spectroscopy. Please site your sources.

3. a)

What does it mean for a planet to be "differentiated"? Why is it important and what are different methods that are used to tell if a planet has been differentiated? What is isostasy and what does it tell us about the interior of a planet?

Undifferentiated bodies are ones that are the same on the surface as they are inside. By contrast, differentiated bodies have had periods of melting and thus have different layers. From the density, we can tell if there are heavier metals internally then we see on the surface. The moment of inertia can also be used to calculate mass distribution inside the planet.

Isostasy is when a planet tries to maintain a constant gravitational potential energy. As a result, in areas where the mantle is sunken, the crust will be higher.

Using your notes, your book, the web, journals, and whatever resources you want, show the geographical history of Mercury through at least 3 images. This will probably be easiest to do through cross-sectional diagrams of the planet, but you could do it through surface diagrams if you wish. Feel free to use more than 3 diagrams, if you feel it is necessary to show the different stages.


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Last updated on 28 May, 2004 .