Planetary surfaces & geologic processes.
1. Describe the history and current location of H2O, if any,
on (a) Mars, (b) Venus, and (c) Io. [6 points]
2. Name at least one planet besides Earth and at least one satellite
that could have once had large oceans of liquid water. Cite evidence. [4
points]
3. (a) What does the layered structure of the martian polar deposits
imply about the history of martian climate? (b) Cite 3 lines of evidence
for climate change on Mars. [4 points]
x
5. Assuming radiative equilibrium (see below):
(a) At which distances from the sun (in AU) will an icy body show cometary activity? [3 points]
(b) Can main belt asteroids, with semi-major axis a ~ 2 - 3.5 A.U., be made substantially of water ice? [4 points]
(c) Discuss implications for stable ground ice on Ceres (semi-major axis = 2.77 AU, albedo = 0.11), for which Dawn data indicate subsurface ground ice at polar latitudes. [3 points]
Show all calculations. HINT: For radiative equilibrium, set the incident flux (Fin) of light absorbed on a rotating planetary surface equal to the flux of light radiated from the planet (Fout). (This equality reflects conservation of energy.) Assume that ice on the surface of this body will sublimate when temperatures reach 273 K or higher, and that this will result in apparent cometary activity. For part (a), perform calculations for a representative mid-latitude (p = 30 degrees) on a rotating body with (a) an albedo A = 0.7 ( a comet with fairly clean ice exposed at the surface; take this as an upper limit to the albedo), and (b) with an albedo A = 0.03 (a comet mantled by dark carbonaceous material; take this as a lower limit to the albedo). Formulas: Fout = (1-A)/pi * cos p * F/a2 where A = albedo, pi = 3.1415, p = latitude on rotating body, F = solar flux at 1 A.U. (solar constant) = 1.36 x 103 J/m2s, and a = distance from sun in A.U.; Fin = e S T4 where e = emissivity (assume 0.2), S = Stefan-Boltzman constant (= 5.67 x 10-8 J/m2K4s), and T = temperature in degrees K .
Petrology
6. How would discovery of wide regions of granite on Venus imply a history
different from that implied by discovery of a wholly basaltic or gabbroic
crust? [2 points]
7. Why is Mars red, and what does this imply about the geologic history
of Mars? [2 points]
8. Why might evaporite deposits be common on some outer solar system
satellites if they had near-surface heat sources such as tidal heating
or radiogenic heating? What surface material is most common on these bodies
in the absence of such heating? In your answer, discuss Io. [3 points]
Interplanetary worldlets.
9. (a) Assuming that manned space vehicles continue to evolve, what
materials do meteorites suggest might be available in interplanetary space
that would be useful in space exploration? (b) Depending on the destination,
why might it cost less energy (hence money) to haul raw materials from
a near-Earth asteroid (approaching Earth at, say, 5 km/s) than to haul
the materials from Earth's surface? For part b, estimate the ratio of energy
required to obtain material from the earth to the energy required to obtain
material from the approaching asteroid. [6 points]
10. Describe some possible solutions to the paradox that most belt asteroids
are C type, whereas only a small fraction of meteorites are carbonaceous
chondrites. [2 points]
11. Give some lines of evidence that many asteroids melted very early
in their histories but that the melting was not smoothly correlated with
asteroid size. [3 points]
Planetary atmospheres.
12. Why is a cloudy night likely to be warmer than a clear night if
other conditions are the same? Why is a night in a clear, high desert colder
than a night on the beach if the noontime temperatures are the same? Relate
these events to the greenhouse effect. [3 points]
13. Optical depth is a dimensionless quantity that expresses the amount
of light intensity lost for a beam of light. For an optical depth of 1,
light is dimmed by a factor of ~2.7 (i.e., a value of e1). Describe
the surface climate on an imaginary planet in Earth's orbit with an atmosphere
that has white clouds of optical depth 10 in the visual region of the spectrum
but optical depth 0.1 in most of the infrared. [2 points]
Solar nebula and planet formation.
14. Why does Titan, which resembles a terrestrial planet, have a nitrogen-methane
atmosphere when terrestrial planets have nitrogen-carbon dioxide-water
vapor atmospheres (or volatile inventories)? [3 points]
15. You are traveling through space and come to a star of normal solarlike
composition, but with planets composed of refractory silicate minerals
rich in aluminum, titanium, and calcium, and containing no water or ice.
What can you conclude about formation conditions? [2 points]
16. Citing their distance from the sun, temperature history, and gravity,
give two reasons why the giants planets have so much more volatile and
icy material and mass than do terrestrial planets. [3 points]