Outer or Jovian Planets
•
•
•
•
•
•
All the Jovian planets are larger than the Terrestrial planets.
All have similar compositions and are similar to the Sun.
Solar composition is mostly Hydrogen, some Helium, etc.
All have low average densities,
All have rings and many satellites.
None have surfaces but only increasingly dense atmospheres
2
and rock and metal cores.
Some of the unmanned spacecraft sent to the Outer Planets
Cassini
Ulysses
Pioneer 10 & 11
Voyager 1 & 2
Galileo
3
Jupiter
Unmanned missions to Jupiter:
• Cassini - Mission to Saturn via Jupiter
(2000)
• Galileo Orbiter & Probe (1995-2003)
• Voyager 1 & 2- Mission to Jupiter
(1979), Saturn, Uranus, Neptune, and
beyond
• Ulysses - (1992- present) Mission to
study the Sun via Jupiter
• Pioneer 10 & 11(flyby 1973, 1974)
• Largest planet in the Solar
System
• Rotates more than twice as fast
as Earth this causes it to appear
slightly flattened at the poles.
• Jupiter emits more heat than it
receives from the Sun.
• The Great Red Spot is a cloud
feature that has been observed
from Earth for several hundred
years!
• Jupiter is a strong source of
radio waves due to its powerful
magnetic field and its
interaction with its moon, Io.
• Atmosphere is a mix of 4
methane, ammonia, and water
Jupiter’s Moons
Ganymede, Callisto, Io, Europa, the
4 largest of the more than 60 moons
orbiting Jupiter
Io is volcanic due to tides raised by the
gravitational pull of Jupiter and the other
moons.
• The four largest moons of Jupiter
(Io, Europa, Ganymede and
Callisto) are known as the
Galilean satellites after Galileo.
• They are roughly the same size as
our Moon although the largest
one, Ganymede, is larger than the
planet Mercury.
• Io, the closest moon to Jupiter, is
the most volcanically active body
in the Solar System!
• Europa, the second closest moon
from Jupiter, is completely
covered in ice. There might be an
ocean beneath the ice and
conditions suitable for life!
5
Roche Limit and Tidal Friction
The Discovery of Radio Emissions from Jupiter
• This discovery was made here in Maryland in Montgomery
County, about 20 miles west of the Washington Beltway.
• The discovery was made using a radio telescope known as the
Mills Cross Array.
• The Mills Cross Array was composed of many antennas
connected together that worked as one huge antenna.
courtesy DTM/CIW archives
7
The Mills Cross Array from the ground
The receivers were housed in an army surplus truck visible in the distance. Undated photo about 1954.
Courtesy of the Archives of the Carnegie Institution of Washington
8
Crab Nebula
• The Mills Cross
Array pointed nearly
at the zenith, the
Earth’s spin allowed
objects to move in
and out of view of
the antennas.
• In early 1955 near
the time of transit of
the Crab Nebula,
Burke and Franklin,
two scientists from
the Carnegie
Institution of
Washington noted
intermittent bursts of
strong radio noise in
about 1/3 of their
records.
from Burke and Franklin [1955]
9
How did they determine that the radio waves were
coming from Jupiter?
• They noticed that the timing of the bursts changed at a
sidereal rate, that is at the same rate that the stars appeared
to move across the sky so it had to be coming from
something in space and not something on the ground.
• Further observations showed that the bursts were actually
drifting slightly, (could it be a planet?).
• Only Jupiter was overhead at the same time as these bursts
were detected and drifted at the same rate.
• Burke and Franklin announced their discovery on April 6,
1955 at the American Astronomical Society meeting in
Princeton, NJ.
10
Jupiter’s “Decametric” Emission
• These radio waves have
wavelengths that are a few 10s of
meters long, so they are called
“decametric”.
• The Jovian emission discovered by
Burke and Franklin in 1955 is
thought to be emitted in a hollow
cone pattern near Jupiter’s north and
south magnetic poles.
• Only when Earth lies in the direction
of one of these cones can we receive
radio waves.
• In 1964, it was found that Jupiter’s
moon Io strongly influences the
radio emission source.
• The Io-related decametric sources
are near the field lines passing
through Io.
Radio
Emission
Aurora
Io
Radio
Emission
11
Jupiter’s Van Allen Belts
- the “Decimetric” Emission
• Both Jupiter and Earth are
surrounded by zones or belts of
high energy particles. These are
known as the Van Allen Belts.
• In 1959 scientists proposed that
the microwave emissions
observed from Jupiter could be
due to Jupiter’s Van Allen Belt.
• Microwaves have wavelengths
of about 1/10 of a meter so they
are called decimetric waves.
• In 1960 scientists confirmed
that the microwaves are coming
from a region along Jupiter’s
equator and a few Jupiter radii
away from the planet.
A recent image of Jupiter made by
observing microwaves of 13 cm
wavelength or 2.3 GHz frequency.
12
Jupiter's Aurora
13
Earth's Aurora
14
Jupiter’s Atmosphere
• General convection
pattern:
– Heat within Jupiter
carries gas to the top of
the atmosphere
– High altitude gas
radiates into space,
cools and sinks
Jupiter’s Atmosphere
• Coriolis effect turns rising and sinking gases
into powerful jet streams (about 300 km/hr)
that are seen as cloud belts
Jupiter's Wind Shear
The winds in adjacent bands move in opposite directions.
Saturn
Saturn as seen from one of the Voyager
spacecraft. A crescent Saturn is
impossible to see from Earth.
Unmanned missions to Saturn:
Cassini/Huygens - (2004-present)
Voyager 1&2 - NASA Missions to Jupiter,
Saturn (1980,1981), Uranus, Neptune, and
beyond
Pioneer 11 - (flyby 1979)
•
Spectacular rings surround the planet.
Saturn has at least 33 moons.
• The rings are composed of chunks of ice
and rock of various sizes most just a few
inches across.
• One of Saturn’s moons, Titan, has a thick
atmosphere and may be covered in ices
composed of nitrogen or ethane.
• The Cassini mission arrived at Saturn in
2004 and will spend 4 years orbiting the
planet. In 2005 the Huygens probe landed
on the surface of Titan.
Infrared image reveals wind shear bands as
seen on Jupiter. These bands are below the
featureless ammonia clouds (upper left image).
18
Saturn’s Moon Titan
• Saturn’s moon Titan is larger
than the planet Mercury.
• Titan’s surface is very hard
to observe due to Titan’s
opaque atmosphere.
• Results about Titan from the
Huygens Lander:
– Titan’s surface temperature
is -179° C (-290° F)
– Instead of liquid water, Titan
has liquid methane. Instead
of silicate rocks, Titan has
frozen water ice. Instead of
dirt, Titan has hydrocarbon
Images like this one particles settling out of the
from Voyager were atmosphere, and instead of
among the best we had lava, Titanian volcanoes
until the spew very cold ice.
Cassini/Huygens
mission
19
Infrared-light image reveals cloud structure below methane layer.
Uranus
• The blue color (see first slide) of
Uranus and Neptune is mainly
due to methane.
• Its rings are narrow and dark.
• The spin axis of Uranus is tilted
so that it lies nearly in its orbital
plane.
• Uranus has more than 20 moons.
• The rings and moons all orbit the
planet so that they are also tilted
the same way as the planet.
• This tilt causes one pole to be in
perpetual day for part of its orbit.
Unmanned mission to Uranus:
Voyager 2 (1986)
20
Neptune
• Sometimes the farthest
planet from the Sun.
• Has dark, narrow rings.
• Neptune has more than 13
moons.
• Triton, one of Neptune’s
moons has strange geysers
erupting from its surface and
has a thin atmosphere.
• Triton orbits backwards and
at high inclination. This
might mean that it was
“captured” by Neptune. It
might be a Kuiper belt
object. May also be similar
to Pluto.
Unmanned missions to Neptune:
Voyager 2 (1989)
21
Pluto
• Is not really a Terrestrial nor a Jovian
planet, its composition is mostly rock
and ice.
• Has the most elliptical and inclined
orbit of all the planets
Current best images of
• Sometimes the farthest known planet
Pluto (small figures) and
from the Sun.
computer enhanced versions
• Has one moon, Charon.
(large figures).
• Pluto and Charon are locked in a
spin-orbit resonance so they always
have the same side facing one
another.
• Like Uranus, is tipped on its side.
• Is the smallest of all the planets, even
Neptune’s moon, Triton.
smaller than our Moon.
22
Pluto might look like this.
Comet Hale-Bopp
(notice yellow dust tail and blue ion tail).
Comets
• Comets are composed of a solid
nucleus, surrounded by a coma
and two tails.
• Comets have a dust tail and an
ion tail.
• The tails form when gas and
dust from the nucleus is pushed
back due to the pressure of sun
light and the fast-moving solar
wind.
• Comet tails always point away
from the Sun.
• Tails generally don’t form until
the comet is about 1 AU from
the Sun. Comas generally don’t
form until the comet is less
The nuclei of Halley’s Comet and Wild2
than 5 AU from the Sun 24
Comets
• Some comets come from the
Oort cloud others are from the
Kuiper Belt both are beyond the
orbit of Pluto.
• Comets have very elliptical
orbits. Some have orbital periods
of decades others have periods
of thousands of years.
• Comet nuclei are basically “dirty
snowballs” since they contain
both ice and dust.
• The dust that comets leave
behind in their orbital path
sometimes hits the Earth and we
see them as meteor showers.
25
Asteroids
Mathilde(left) and Eros(right),
two asteroids observed by the
NEAR spacecraft. NEAR orbited
and eventually landed on Eros.
Eros is about 22 x 8 x 8 miles.
• Most asteroids orbit
between Mars and Jupiter
but there are some that
cross the orbit of the Earth
and other planets.
• Most asteroids are not
large enough to form into
spheres.
• Ceres, one of the largest
asteroids, is about 1000
km in diameter (less than
half the size of Pluto) and
is spherical.
26
Asteroids
Eros again now shown to scale
with Vesta(artist conception) and Ceres
the two largest asteroids.
• Some asteroids
may have been
fragments from
larger bodies
that had
differentiated
into metallic
cores and stony
crusts.
• Other asteroids
seem to have
compositions
that might be
very similar to
the original solar
nebula.
27