Download Day-37

Astronomy 1010
Planetary Astronomy
Fall_2015
Day-37
Course Announcements
•
SW-chapter 11, 12 due: Mon. Dec. 7
•
Lab this week is Comparative Planetology … this one
you can do on your own and turn in.
•
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Next week is the make-up week for labs …
We will have the equipment for Lenses & Telescopes
and the Spectrometer set up. These are the only two
that will be setup in lab. Any other labs (computer
based) must be completed PRIOR to Tuesday. I will
have a substitute for the cratering lab for those that
need it.
 Dozens of “worlds” of rock and ice exist in our
Solar System; some large, some small.
 Liquid water under some surfaces is possible.
 The moons are made of rock, ice, or both.
 Some were formed by accretion and
differentiation.
 They have many diverse properties, only
partially understood.
 Most of the larger moons formed with their
planets through the processes of accretion
and differentiation.
 These are called regular moons.
 They revolve around their planets in the
same direction that they rotate.
 Almost all are tidally locked, meaning one
hemisphere always faces the planet the
moon is orbiting.
 Some moons are objects that formed apart
from a planet, but were later gravitationally
captured by one.
 These are called irregular moons.
 They are usually on retrograde
(“backward”) orbits.
 Largest: Triton, moon of Neptune.
 Many are only a few kilometers across.
 The giant planets have several large moons,
and many are as large as Earth’s Moon.
 Some are geologically active, while others
used to be.
 Surface markings, craters, and bright/dark
areas reveal geological activity.
 Categorized as active now, possibly active,
active in the past, and never active.
 For a moon to be
geologically active,
it must have internal
heat.
 Tidal stretching by
a planet heats the
moon’s interior.
 Analogy: flexing a
paper clip.
 Example: Jupiter’s
moon Io.
 Io is the most
volcanically active
object in the Solar
System.
 Eruptions of silicate
magmas.
 Has no craters and
a very young
surface.
 For a moon to be
geologically active,
it must have internal
heat.
 Tidal stretching by
a planet heats the
moon’s interior.
 Analogy: flexing a
paper clip.
 Example: Jupiter’s
moon Io.
 Io is the most
volcanically active
object in the Solar
System.
 Eruptions of silicate
magmas.
 Has no craters and
a very young
surface.
 Enceladus (Saturn): partially young surface.
 Experiences cryovolcanism, in which the
“magma” is water.
 Thermal energy melts ice and drives it up to
the surface.
 Enceladus’s low gravity cannot hold onto the
icy particles once they are ejected.
 This is the source of material for Saturn’s
faint E Ring.
 Triton is an irregular moon of Neptune with a
retrograde orbit.
 Cantaloupe-like surface is a clue to its
activity.
 Cryovolcanic activity: geysers of nitrogen.
 Thin atmosphere.
 Europa (Jupiter) is possibly active.
 Jupiter’s tidal heating should be too low for
volcanism, but should allow for subsurface
liquid, perhaps as underground lakes.
 Broken slabs of ice that appear to have
floated and collided suggest geologic activity.
 Titan is Saturn’s largest moon.
 It has a thick, dense, nitrogen-rich
atmosphere.
 Huygens lander revealed icy “rocks” and a
soil rich with organic compounds.
 Possibly active.
Possibly Active: Titan
 Methane appears to experience a cycle like
rain on Earth, involving methane lakes and
clouds.
 Methane in Titan’s atmosphere is most likely
renewed by active geology.
 Formerly active
Ganymede (Jupiter) is
the largest moon in
the Solar System.
 Signs of gradually
filled-in craters.
 Bright terrain from
some unknown past
tectonic processes.
 Some moons of
Saturn and Uranus
also appear this way.
 Other moons show signs on the surface of
being formerly active, including bright and
dark areas and tectonic fracturing.
 Examples: Mimas and Iapetus of Saturn;
Miranda of Uranus.
 Callisto (Jupiter)
shows no sign of early
geologic activity.
 Dark, heavily cratered
surfaces.
 Bright regions where
subsurface ice has
been exposed after
impacts.
 Others include
Umbriel (Uranus).
i_Clicker Question
Jovian Planets: Europa’s Oceans
Ring Systems
 All four gas giants
have ring systems.
 Saturn’s rings are
the largest and
brightest.
 The fainter rings
were discovered
by stellar
occultation
methods.