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Astronomy 1010
Planetary Astronomy
Fall_2015
Day-38
TNO_Wide-1
Course Announcements
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SW-chapter 11, 12 due: Mon. Dec. 7
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1st Thursday Art Walk – 5-8pm on Study Day
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This 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.
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.
 A very complicated system, composed of
thousands of ringlets, each made up of tiny
orbiting particles that obey Kepler’s laws.
 There are bright and dark rings, “gaps,” and
divisions.
MATH TOOLS 11.1
 The moons obey Kepler’s laws as they orbit
the planet:
 For a particular planet, the left-hand side will
be a constant for most of its moons.
 For Jupiter, Ganymede, Europa, and Io are in
an orbital resonance of 1:2:4.
 Can estimate relative orbital distance.
 Gaps are not empty.
 Brightness/darkness
reflects the amount
of material in each
ring.
 Though wide, the
ring system is
extremely thin.
 If Saturn were a
basketball, a piece
of paper is >1,000
times too thick.
 Diffuse rings are fainter and have no
defined boundaries.
 Saturn’s largest ring is a diffuse dust ring,
discovered in 2009.
 E Ring and G Ring are also diffuse.
 The rings of the other giant
planets are mostly narrow
and diffuse.
 Backlighting brings them
into view.
 Neptune has denser
sections known as ring
arcs.
 Ring particles are from disrupted moons or
from volcanic activity on moons.
 Saturn: bright rings because they are
made of water ice.
 The total mass of Saturn’s bright rings is
about the same as a small icy moon.
 Uranus and Neptune: dark rings from
organic material (darker than coal).
 Jupiter: not as dark as the ice giants, nor
as bright as Saturn’s; most likely
composed of dark silicates.
 Rings are kept stable by shepherd moons.
 Shepherd moons can also distort rings.
 Gravity can cause distortions, including what
look like twists and waves.
 Other
distortions
include
scalloped
shapes and
appearance of
transient
spokes in
Saturn’s rings.
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Rings do not last forever.
Collisions and sunlight destroy rings.
Shepherd moons can help stabilize rings.
Orbital resonances can create gaps.
Earth does not have a ring because it
lacks shepherd moons to contain the
material.
i_Clicker Question
Jovian Planets: Saturn Ring Gaps
Jovian Planets: Shepherd Moons
MATH TOOLS 11.2
 The tidal force between a planet and its
moon depends on their masses, the size of
the moon, and the distance between them:
 Can use this to find the relative tidal forces
for different moons of the same planet.
MATH TOOLS 11.3
 The moons of the giant planets have a much
lower escape velocity than that of Earth,
which is 11.2 km/s or >40,000 km/h.
 Cannot easily hold on to particles ejected
during volcanic activity.
 Enceladus:
 Its cryovolcanic plumes are nearly 2,200
km/h.
 The identification of extremophile bacteria
on Earth has led to consideration of the
possibility of life in the extreme
environments of the Solar System’s
moons.
 The combination of liquid water, heat, and
organic compounds could be present.
 Enceladus, Europa, Titan, and Callisto are
possibilities for life.
CONNECTIONS 11.1
 Small particles are best viewed when they
are between the observer and light source.
 Backlighting allows for the rings of the planets
to be viewed most easily.
 Most light that hits the particles still comes to
the observer instead of being scattered away.
PROCESS OF SCIENCE
 Apparent violations
of well-supported
theories are exciting
for scientists
because they must
be reconciled.
 This often means
that something new
is about to be
discovered.
 Planetesimals left over from the formation
of the solar system include asteroids and
comets, as well as meteorites and
meteroids.
 Five large planetesimals deserve their own
classification: dwarf planets.
 Four reside in the Kuiper Belt beyond
Neptune’s orbit: Pluto, Haumea,
Makemake, and Eris.
 Ceres is in the main asteroid belt.
 Pluto is about
1/400 the mass
of Earth.
 “Double planet”:
Pluto/Charon.
 Eccentric orbit.
 Rock and ice.
 Thin methane
atmosphere.
 Eris, larger than Pluto, is
the most distant.
 Has moon, Dysnomia.
 Orbit has greater
inclination than Pluto’s.
 Ceres used to be known
as the largest asteroid.
 Spherical, about 4% the
mass of the Moon.