1. Seasons Revisited
Jupiter's `North Pole' points directly up relative to its orbit - that
is, Earth's tilt is about 23°, and Jupiter tilt is only 5°.
(Uranus' is slightly over 90°). Describe the seasons on Jupiter:
how strong would they be, and how much could they affect the interior
of the planet? How does this compare with Earth? Hint: be sure to
consider all the sources of heat for Jupiter and the Earth.
The Earth's moderate seasons are caused by its 23° tilt, and Uranus' rather extreme seasons are caused by its 90° tilt. Since Jupiter is only slightly tilted - and because it's on only a moderately # eccentric (elliptical) orbit - its seasons are quite mild. In addition, since Jupiter gets just as much heat from its core as from the Sun, the daily temperature throughout the year varies even less.
2. A miniature Solar System
Discussion Question 1, Ch. 11 in the text (p. 338).
Similarities: they orbit Jupiter; they each have geology; characteristics are based on their distances; density decreases further outward; outer bodies are more heavily cratered and less interesting; all orbit in same direction and plane, etc.
Differences: Jupiter isn't the main heat source; they're in a tight resonance; strong magnetic field; closer relative distances; and any number of other things.
3. Comparing Jovian Planets
Problem 3, Ch. 11 in the text (p. 338).
a) Using Kepler's 3rd law, we deduce that Saturn has a lower mass than Jupiter.
b) Since Saturn's mass is lower but their radii similar, Saturn's density must be lower than Jupiter's.
4. Cosmic Collisions
Uranus' moon Miranda
appears to have been violently fragmented in the past, and then
re-accreted together. The best theory for
the formation of our Moon says we went through a similar collision: the
Earth was hit by a Mars-sized impactor about 4 billion years ago,
spewing debris into orbit around the Earth which accreted to form the
Moon. However, neither the Moon nor the Earth show evidence for this
as dramatically as Miranda does. Think of some possible reasons for
this. Hint: Consider the relative sizes of Miranda and the Earth/Moon
and what effect this would have on their surfaces and atmospheres, and
the fact that Miranda was his by a much smaller object than hit the
Earth.
Miranda is much smaller than the Earth or Moon, so any scars from an impact (which we definitely see) are going to stick around for a long time because there's no volcanism, tectonics, or erosion. Miranda is too small to support any of these processes, since it cools off quickly and can't maintain an atmosphere. Earth's size implies that its interior is warm and it can still differentiate; Miranda is cold throughout and therefore has only barely been smooshed (e.g., into a sphere) since its breakup and. Also, the Earth-Moon collision was far longer ago (4.5 Byr), so any direct evidence has had far longer to be lost.
5. Life from the Ooze
Titan, Europa, and Mars have all been proposed to have oceans currently
or in the past, and as possible places for life. Discuss the evidence
for liquid water on each one. Which do you think is most likely to
have life? Why?
Titan: no liquid water, but there's thick methane clouds, and likely methane oceans. Mars: we've seen river channels that show solid evidence for rivers on the surface quite recently. Europa: since there's no impact craters, the ice surface is quite young, and we see that it has been broken up recently and we see parts of it that have `rafted' around the surface like icebergs, suggesting they were floating on a global ocean quite recently. Which one is best for life? That's anyone's guess: could be any of these!
Last modified 27-Jun-2000