Download Announcements THE OUTER PLANETS

11/17/16
Announcements
!  Tonight’s observing session is on!
!  The 8th LearningCurve activity was due earlier today
!  Assignment 8 and Quiz 8 will be due on Tue. Nov. 22
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THE OUTER PLANETS
!  This section deals with the 4 planets whose orbits lie
outside those of the terrestrial planets
!  These outer planets are called gas giant planets
!  Jupiter, Saturn, Uranus, and Neptune
!  Pluto is much smaller, and is no longer classified as a
regular planet
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Exploration of the Outer Planets
!  Pioneer 10 was launched in
March 1972
!  In Dec. 1973, it became the
first spacecraft to pass close
to Jupiter
!  It came within 130,000 km of
Jupiter’s cloud-tops, and
returned the first ever
close-up images
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Pioneer 11
!  Pioneer 11 left Earth in April
1973
!  It passed close to Jupiter in
Dec. 1974
!  It later flew to within 20,000
km of Saturn in Sept. 1979
!  Pioneer 11 returned the first
close-up pictures of Saturn
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Voyager 1 and 2
!  NASA’s Voyager 1 spacecraft
flew by Jupiter in 1979, and
Saturn in 1980
!  Voyager 2 flew by:
!  Jupiter in 1979
!  Saturn in 1981
!  Uranus in 1986
!  Neptune in 1989
!  To this date, no other
spacecraft has visited Uranus
or Neptune
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The Paths of Voyager 1 and 2
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The Galileo Orbiter and Probe
!  The Galileo spacecraft
arrived at Jupiter on Dec. 7,
1995, after a 6-year trip
!  Upon arrival, it also released
a small probe, which
parachuted into Jupiter’s
atmosphere
!  Galileo was crashed into
Jupiter in 2003
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The Cassini Mission to Saturn
!  NASA’s Cassini spacecraft
arrived at Saturn in July
2004
!  it remains in orbit around
Saturn, and continues to
make flybys of its moons !  It sent a probe (Huygens) to
the surface of Titan in
January 2005
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The JUNO Mission to Jupiter
!  NASA’s JUNO spacecraft arrived in orbit around
Jupiter on July 4, 2016
!  It will study the atmosphere and interior of Jupiter
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Recent Images From JUNO
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Jupiter
!  Jupiter is the fifth planet
from the Sun
!  its average distance from the
Sun is 5.2 AU
!  It takes about 12 years to
orbit the Sun
!  Jupiter rotates once every 10
hours
!  this is the fastest of all the
planets
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Jupiter’s Size and Mass
!  Jupiter is the solar system’s largest planet
!  its diameter is ~11 times larger than Earth’s
!  if it were hollow, 1300 Earths could fit inside it!
!  It is also the most massive planet
!  this means it contains the most mass
!  it is 318 times more massive than the Earth
!  it is more than twice as massive as all of the other
planets combined!
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Jupiter’s Cloud Layer
!  Jupiter is always covered in
clouds, which lie in a layer
that is 50 km thick
!  These clouds are made
primarily of sulphur, water,
and ammonia compounds
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Jupiter’s Great Red Spot
!  Many features are seen in
the cloud layer
!  Atmospheric bands encircle
the planet
!  Many storm systems are seen
!  The largest – called the
Great Red Spot – has been
around since at least 1665!
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Close Up of the Great Red Spot
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Jupiter’s Atmosphere
!  Below the clouds, there is a 20,000 km thick layer of
hydrogen and helium
!  this layer gradually changes from gas to liquid as the
depth (and pressure) increases
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Jupiter’s Interior
!  Below the liquid hydrogen is a 40,000-km thick sea of
liquid metallic hydrogen
!  this dense material is probably responsible for Jupiter’s
powerful magnetic field
!  In the centre there is an even denser core of iron, rock
and water
!  it is unclear if this layer is solid or not
!  even if solid, the atmospheric pressure would be far too
great for a person to stand or walk
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Jupiter’s Moons
!  Jupiter has at least 67 moons
Io
Europa
(more than 1/3 of the 173
known solar system moons)
!  this total is for the moons of
the 8 modern day planets
Amalthea
!  Galileo discovered the four
largest moons in 1610
!  they are known as the
Galilean moons
!  The remaining 63 known
moons are much smaller
Ganymede
Callisto 18
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Ganymede
!  Ganymede is the largest moon
in the solar system
!  it is also larger than Mercury
and Pluto
!  its diameter is 5200 km
!  It has frosty polar ice caps
and a thin atmosphere
!  It has an iron-rich core, a
rocky mantle, an ice/water
layer, and a surface of dirty
ice
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The Interior of Ganymede
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The Surface of Ganymede
110 km
!  The icy surface of Ganymede
has many impact craters
!  this implies that its surface
is very old
!  It is also crisscrossed by
grooves and ridges
!  these unusual features
appear to be tectonic in
nature
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Callisto
!  Callisto is Jupiter’s second
largest moon
!  It is the outermost of the
Galilean moons
!  It takes about 17 days to
orbit Jupiter
!  Its icy surface is mostly
covered by dark dust from
meteorites
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Callisto’s Impact Basins & Craters 23
Callisto’s Interior
!  Callisto’s core is composed
mainly of rock and ice
!  The crust is 200 km thick
and is made mostly of ice
!  There may be a thin ocean
of salt water in between
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Europa
!  Europa is the smallest Galilean
moon
!  Its icy surface is very smooth
and few craters are seen
!  This implies that its surface is
very young
!  the oldest regions are only
about 10 million years old
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The Surface of Europa
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Sea Salt on Europa?
A recent study indicates that the red linear features on the surface of Europa
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are consistent with sea salts which have been exposed to radiation.
HST Evidence of Water Vapour Vents
!  Recent images and spectra from the Hubble Space
Telescope (HST) appear to have detected water
vapour vents near Europa’s south pole
!  These are thought to have been emitted from cracks
on Europa’s surface
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The Interior of Europa
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How Much Water is in Europa’s Oceans?
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A Salt Water Ocean on Europa?
!  The water layer may contain
an ocean of salt water
!  this layer contains more
water than all of the Earth’s
oceans combined
!  It is possible that life exists
within this ocean!
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Io
!  The innermost of the Galilean
moons is named Io
!  It is one of the most unusual
moons in the solar system
!  Its surface is rich in sulphur,
giving it distinctive colours
!  Io has no impact craters!
A true-colour image of Io
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Volcanism on Io
!  In 1979, the Voyager
spacecraft observed 9
different volcanoes erupting!
!  Io is the only place (besides
Earth) where active
volcanoes have been seen
!  The volcanism on Io is due to
tidal stresses from Jupiter,
Europa and Ganymede
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Io’s “Ra Patera” Shield Volcano
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A Recent Eruption on Io
Recent eruption (Nov. 1999)
Active eruption (Feb. 2000)
250 km
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The Effects of Volcanism on Io
!  Erupting volcanoes blast sulfurous gas and ash over the
surface of Io, wiping out any newly formed craters
!  Despite ongoing volcanism, Io’s surface is mostly very
cold (about -143° C), so some sulphur dioxide frost can
be seen
!  however, no water or ice is present on Io
!  It is estimated that volcanism completely resurfaces Io
every million years or so
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Jupiter’s Smaller Moons
!  Jupiter has at least 63 small moons
!  The largest of these is only 250 km across
!  All of these small moons were probably captured
after Jupiter and its Galilean moons had formed
Amalthea
Thebe
Metis
Galileo
Images:
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Jupiter’s Rings
!  Jupiter also has a very faint system of rings
!  These rings are made of tiny particles of rock dust
that are orbiting around Jupiter
!  This dust probably originates from meteoroid impacts
on Jupiter’s tiny inner moons
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Schematic of Jupiter’s Rings
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Saturn
!  Saturn is the second largest
planet in the solar system
!  At 9.5 AU, it is nearly twice
as far out as Jupiter, and
orbits the Sun every 30
years
!  Its rotation period is about 11
hours
!  Saturn is best known for its
distinctive rings
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Saturn’s Atmosphere
Saturn’s atmosphere is similar to Jupiter’s, with numerous storms.
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A Storm on Saturn in 2011
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Lightning on Saturn!
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Saturn’s Polar Vortex
This near-infrared image from Cassini shows the six-sided jet stream
surrounding a 2000-km wide red hurricane-like system at the north pole.
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Saturn’s Interior
!  Saturn’s interior is similar to Jupiter’s, though less dense
!  Its rocky core is about 32,000 km in diameter
!  Saturn also has a strong magnetic field
!  This is produced by its layer of liquid metallic hydrogen
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Persistant Aurorae on Saturn
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Saturn Eclipses the Sun
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The Makeup of Saturn’s Rings
!  Saturn’s rings are not solid, but instead are made up of
numerous small particles
!  most are the size of dust particles up to a few cm in size
!  These particles are made of ice and rock
!  These particles all orbit Saturn under the influence of
its gravitational attraction
!  the inner particles orbit the fastest
!  in fact, all of the particles obey Kepler’s Laws
!  Saturn’s main ring system is about 380,000 km wide but
only about 10 m thick!
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Saturn’s Rings as seen by Cassini
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Cassini’s View of Saturn’s Rings
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Gaps in Saturn’s Rings
!  Many divisions are seen in the ring system
!  in fact, there are thousands of distinct ringlets!
!  Some gaps in the rings are due to resonances with
Saturn’s larger moons
!  at some distances from Saturn, ring particles cannot stay
for long, so these regions are relatively empty
!  Other spaces between rings are kept clear by tiny
moons which orbit within the rings
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Moons within Saturn’s Rings
Encke gap
F Ring
Pandora
Prometheus
Pan
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The Orientation of Saturn’s Rings
!  Saturn’s appearance depends
on the orientation of its rings
with respect to us
!  When its rings are aligned
with Earth, they are hard to
see
!  At any other time, they are
hard to miss!
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Saturn Seen From Above (by Cassini)
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Saturn Seen Edge-on by Cassini
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How Did Saturn’s Rings Form?
!  Saturn’s ring system may have
formed when a Titan-sized
moon was accreted by Saturn
early in its history
!  This moon would have
migrated inward within a disk
of gas that orbited Saturn
!  The icy outer layers would
have been stripped off before
this moon fell into Saturn
!  Some of this icy material
remains in orbit around
Saturn, making up its main
ring system
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Saturn’s Moons
!  Saturn has at least 62 moons
!  many of these moons were discovered by Cassini
!  Most of Saturn’s moons are very small and non-
spherical
!  they are probably captured asteroids
!  Saturn’s largest moon is named Titan
Prometheus
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Saturn’s Moon Titan
!  Titan is the second largest
moon in the solar system
!  only Ganymede is larger
!  It is surrounded by a thick,
opaque atmosphere
!  this prevents us from seeing
the surface in visible light
!  the atmosphere is made
mainly of nitrogen and
methane
!  Titan is the only moon in the
solar system that has a thick
atmosphere
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Titan’s Haze
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Multiple Layers of Haze on Titan
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The Surface of Titan
Before the Huygens probe arrived
at Titan, there had been
speculation that the surface of
Titan might have:
!  huge mountains of ice (made
of frozen water or methane)
!  hydrocarbon oceans and lakes
!  a smoggy sky and gasoline
rain
Cassini false-colour image
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Descent to the Surface of Titan
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Dry Riverbeds on Titan?
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Huygen’s Landing Site
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Scientific Results From Cassini
and Huygens
!  Smog particles appear to precipitate out of the
atmosphere, falling as dark “dust”
!  Methane “rain” appears to fall occasionally, and this
washes the dust down from the mountains
!  There are clear signs of dry riverbeds and lakebeds
(with bottoms coated in dust)
!  Methane lakes have been found at northern latitudes
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Hydrocarbon Lakes on Titan
!  Cassini has found hundreds
of lakes on Titan
!  these lakes are found only in
Titan’s polar regions
!  Analysis indicates that these
lakes are made of:
!  75-80% ethane
!  7-8% propane
!  5-10% methane
!  5% other compounds
Source: Cordier et al. (2009)
Cassini radar map of lakes on Titan
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Polar View of Titan’s Lakes
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Sunlight Reflecting Off a
Methane Lake on Titan
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A Transient Feature in a Lake on Titan
!  A 20-km long object appeared and later disappeared
in a lake on Titan
!  This could be due to floating ice, bubbles or waves
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Methane Rain on Titan
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Future Exploration of Titan?
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Saturn’s Moon Enceladus
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Ice Plumes on Enceladus
Cassini image from Nov. 2009
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An Ice Volcano on Enceladus
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Tiger Stripes on Enceladus
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Tiger Stripes
!  Thermal measurements from Cassini show that tiger
stripes can be much warmer than their surroundings
!  some are as warm as -80 Celsius
!  this is indicative of volcanic activity, which would be
warm enough to melt some of the subsurface ice
Cassini tiger stripe close-up
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Opening and Closing of Tiger Stripes
!  The elliptical orbit of Enceladus around Saturn creates
higher tidal stress when Enceladus is closest to Saturn
!  High tidal stress compresses Enceladus and causes the
tiger stripes to mostly close up
!  Cassini measurements indicate that plume activity is four
times higher at apocentre than at pericentre
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An Ocean Below the Crust of Enceladus
Analysis of the plume and detailed gravitational measurements
indicate that there is a salty ocean below the surface of Enceladus.
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Uranus
!  Uranus is nearly twice as far
from the Sun as Saturn, at
19 AU
!  Despite being much larger
than the inner planets, it is
too faint to see with the
naked eye
!  It was discovered by William
Herschel in 1781
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The Size of Uranus
!  Uranus has a diameter of about 50,000 km
!  this is equal to about 4 Earth diameters
!  It is barely larger than Neptune, but less massive
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The Rotation of Uranus
!  The rotation axis of Uranus is tilted by about 98°
!  this may be the result of a major collision with an
Earth-sized object at some time in the past
!  As a result, Uranus has the most extreme seasons of
any of the planets
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The Extreme Seasons of Uranus
Note: a Uranus year is 84 Earth years long.
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The Moons of Uranus
!  Uranus has at least 27 moons
!  only 5 moons were known
before 1986
!  Voyager 2 identified 10 new
moons
!  The largest – Titania – is less
than half of the diameter of
our Moon
Titania
(1580 km across)
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The Oberon
Moons of Uranus
Titania
Umbriel
Miranda
Puck
(150 km across)
Ariel
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The Rings of Uranus
!  In 1977, 5 rings were found
around Uranus
!  they were detected when
Uranus passed in front of a
distant star
!  Voyager 2 imaged these
narrow rings, and found 5
others
!  Some of the rings have
shepherd moons
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The Rings of Uranus Seen Edge-on
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The Atmosphere of Uranus
!  Uranus is surrounded by an
atmosphere of mostly
hydrogen
!  It also has some high
altitude methane, which give
it its bluish colour
!  Uranus is almost featureless
in visible light, but does have
clouds and bands
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Neptune
!  The planet Neptune was
discovered by Johann Galle in
1846 !  Its existence had been
predicted, due to its
gravitational influence on
Uranus
!  It is very much like Uranus
in terms of size and overall
makeup
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Neptune’s Orbit and Rotation
!  Neptune lies at a distance of
30 AU
!  Its orbital period (year) is
165 years
!  It rotates once every 19
hours
!  Its rotation axis is tilted by
about 30°
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Neptune’s Great Dark Spot
!  Neptune’s atmosphere is
similar to that of Uranus
!  Voyager 2 discovered a large
storm in 1989
!  this Neptunian storm was
named the Great Dark Spot
!  This cloud pattern was as
large as the Earth!
!  This storm has since
dissipated, but other storms
have been seen
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Neptune’s Moons !  Neptune has 14 known moons
!  13 of these are very small
and irregular
!  The other, named Triton, is
much larger
!  Triton is spherical and a bit
larger than Pluto
!  Triton has an retrograde
orbit around Neptune, which
will cause it to spiral inwards
and be torn apart by tidal
stresses
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Neptune’s Rings
!  Like the other gas giant
planets, Neptune has rings
too
!  It has two main rings, which
are very faint
!  Voyager 2 first verified their
existence in 1989
!  These rings may be
replenished by comets
crashing into Neptune’s inner
moons
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The Interiors of Uranus and Neptune
!  Both Uranus and Neptune appear to have:
!  a rocky core
!  a liquid water mantle
!  a surrounding layer of liquid hydrogen and helium
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Before Next Class
!  Complete Assignment 8 and Quiz 8
!  due on Tue. Nov. 22 at 2 p.m.
!  Read Chapter 9
!  Complete LearningCurve: Vagabonds of the Solar System
!  due on Thu. Nov. 24 at noon
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