3. Jovian Magnetosphere (17 points)
The jovian satellites in order of distance from Jupiter are Io, Europa, Ganymede, and Callisto.
They all orbit Jupiter counter-clockwise as viewed from above Jupiter's north pole. Like all orbiting
objects, the closer moons take less time to orbit Jupiter than the farther moons.
a. (3) The Jovian moons create 'auroral spots' in Jupiter's upper atmosphere that have been
detected by telescopes. Imagine that you are located directly above Io's auroral spot at a given
instant, and that you have a fixed longitude and latitude (i.e. you are rotating with the planet
every ~10 hours). From your perspective, what does Io's auroral spot do next - stay directly
below you, move eastward, or move westward? Support your answer.
b. (3) Now assume that you are located directly above Io's auroral spot in at a given instant, and
that Europa's auroral spot is observed at the same longitude at that moment. Is the latitude of
Europa's auroral spot closer to the equator or farther from the equator than Io's? Support your
answer.
c. (3) Following (b), you stay hovering above Io's spot for an hour and then look back down at
the atmosphere. Where is Europa's spot - at the same longitude, east of you, or west of you?
Support your answer.
d. (3) Ganymede has aurora. Where on Ganymede would you expect to see them, and why?
e. (5) The Jovian magnetosphere is considered by some to be the largest 'object' in the solar
system, with a tail that extends nearly to the orbit of Saturn. What is the angular width of
Jupiter's magnetosphere as seen from Earth when the two planets are 90 degrees apart?
Assume that Earth's orbital distance = 1 AU and that Jupiter's magnetosphere extends from
5.2 AU to 9.2 AU. How does your answer compare to the ~0.5° angular width of the Moon as
viewed from Earth? (A good diagram is essential here! Look for right triangles!)
