Transcript The Giant Planets 18 July 2005 AST 2010: Chapter 10 1

The Giant Planets
18 July 2005
AST 2010: Chapter 10
1
Jovian Worlds
Saturn
Neptune
Uranus
Jupiter
18 July 2005
AST 2010: Chapter 10
2
Missions to Outer Solar System
18 July 2005
AST 2010: Chapter 10
3
Early Exploration of Outer Solar System
Pioneers 10 & 11 were launched in 1972 & 1973
Can they navigate through the asteroid belt?
What are the radiation hazards in Jupiter’s
enormous magnetosphere?
Pioneer 10 flew by Jupiter in 1973 and then sped
outward toward the edges of the solar system
Pioneer 11 flew by Jupiter in 1974 and was
diverted towards
Saturn, which it
reached in 1979
18 July 2005
AST 2010: Chapter 10
4
Further Exploration of Outer Solar System
Voyagers 1 & 2 were launched in 1977
They carried 11 scientific instruments,
including cameras, spectrometers, and
devices for measuring magnetospheres
Their missions were highly productive
Voyager 1
reached Jupiter in 1979, and used a gravity
assist from Jupiter to reach Saturn in 1980
Voyager 2
Voyager
reached Jupiter four month later than Voyager 1
used gravity assists to reach Saturn in 1981, Uranus in
1986, and Neptune in 1989
These multiple gravity-assisted flybys were possible
thanks to the approximate alignment of the planets
Such an alignment occurs about once every 175 years
18 July 2005
AST 2010: Chapter 10
5
Recent Exploration of Jupiter
For a detailed study of a planet, spacecraft that can
go into orbit around the planet are necessary
Flybys of the planet are not adequate
The Galileo spacecraft was launched from the space
shuttle Atlantis in 1989 and arrived at Jupiter in 1995
It began its investigations by deploying a small entry
probe for direct studies of Jupiter’s atmosphere
18 July 2005
AST 2010: Chapter 10
6
Galileo Spacecraft
In September 2003, the Galileo spacecraft ended
its mission by plunging into Jupiter’s atmosphere
18 July 2005
AST 2010: Chapter 10
7
Galileo’s Entry Probe
had a mass of 339 kg
plunged into Jupiter’s atmosphere
at a shallow angle and a speed of
50 km/s
was slowed down by atmospheric
friction
the temperature of its heat
shield reaching 15,000°C
as its speed dropped to 2500 km/h, jettisoned the
remains of its shield and deployed a parachute for
a gentler descent in the atmosphere (animation)
transmitted data to the Galileo orbiter, for
retransmission to Earth
18 July 2005
AST 2010: Chapter 10
8
Some Results of Galileo Mission
A satellite (Dactyl) of an asteroid (Ida) was discovered
Jovian wind speeds in excess of 600 km/hour (400
mph) were detected
Far less water was detected in Jupiter's atmosphere
than estimated from earlier Voyager observations and
from models of the Comet Shoemaker-Levy 9 impact
Far less lightning activity was found than anticipated
The individual lightning events, however, are about ten
times stronger on Jupiter than on the Earth
The helium abundance in Jupiter is very nearly the
same as that in the Sun (24% compared to 25%)
Possible evidence for liquid-water ocean under
Europa's ice was found
Website
Recent Exploration of Saturn
Saturn, with its spectacular
rings and many moons, is
intriguing for many reasons
The Cassini spacecraft was
launched 1997 and reached
Saturn in 2004
It deployed the Huygens probe
into Saturn’s moon Titan in
January 2005
Titan is of particular interest
to scientists because it is
one of the few moons in our
solar system with its own
atmosphere
Animation
Basic Facts about Jovian Planets
They
are at large distances from the Sun
have long orbital periods
rotate (spin) very fast
Jupiter and Saturn have many similarities in in
composition and internal structure
Uranus and Neptune
are smaller than the other two
differ from the other two in composition and structure
Appearance of Jovian Planets
Only the atmospheres of
the giant planets are
visible to us
The atmospheres are
composed mainly of
hydrogen and helium
The uppermost clouds of
Jupiter and Saturn are
composed of ammonia
(NH3) crystals
The upper clouds on Neptune are made of
methane (CH4)
Uranus has no obvious clouds, only deep and
featureless haze
18 July 2005
AST 2010: Chapter 10
12
Rotation of Jovian Planets
How does one determine the rotation rates of the
giants?
For Jupiter
1st option: use dynamic surface features (storms)
However the cloud rotation may have nothing to do
with the rotation of the mantle and core…
2nd option: look at periodic variations of radio
waves associated with the magnetic field produced
deep inside the planet
This gave rotation period of 9 h 56 m
The same technique is used to measure the
rotation of other giant planets
Saturn has 10 h 40 m
Uranus and Neptune have about 17 hours
18 July 2005
AST 2010: Chapter 10
13
Seasons on the Giants
Jupiter’s spin axis is tilted by 3°
It has no seasons to speak of
Saturn’s axis is tilted by 27° and Neptune’s 29°
Both have seasons
Uranus’ axis is tilted by 98°
practically orbiting on its side
its rings and satellites
following the same pattern
causing it to have very
strange 21-year seasons!!!
Uranus’s odd tilt could have
been the result of a giant
impact in its past
Seasons on Uranus
Infrared Image of Uranus
South pole marked with +
Giant Pressures on Giant Planets
Astronomers believe that the interiors of Jupiter
and Saturn are composed mainly of hydrogen (H)
and helium (He)
Their precise internal structure is difficult to predict
Because the planets are enormous, the H and He
in their centers are probably compressed
tremendously
Theoretical models predict that Jupiter has
a central pressure of more than 100 million bars
a central density of 31 g/cm3
The Earth by contrast has 4 million bars and 17
g/cm3 in its center
Giant planets imply giant pressures!!
18 July 2005
AST 2010: Chapter 10
16
Consequences of Enormous Pressure
A few thousand km below Jupiter and Saturn’s
visible clouds, hydrogen is changed from a
gaseous to a liquid state
Still deeper, the liquid hydrogen is further
compressed and begins to act like a metal
On Jupiter, most of the interior is probably
liquid metallic hydrogen!
Since Saturn is less massive, it has only a
relatively small volume of metallic hydrogen
Most of its interior is liquid, but not metallic
Neptune and Uranus are probably too small to
liquefy hydrogen
18 July 2005
AST 2010: Chapter 10
17
More about Composition
Detailed analyses of their gravitational fields
suggest that each of the giant planets has a
core composed of heavier materials
The core may have been the original rock-andice body that formed before gas was captured
from the
surrounding
nebula
The pressure in the
core is in the tens of
millions of bars
At such a pressure,
rock and ice do not
assume their
familiar forms
Internal Heat Sources
Because of their large sizes, all the giant planets are
believed to be strongly heated during their formation
The contraction due to gravity produced heat
Being the largest, Jupiter was the hottest
Some of this primordial heat still remains inside them
Giant planets may also generate energy internally by
slowly contracting
Even a small amount of shrinking can generate
significant heat
These internal sources of heat may raise the
temperatures in the interiors and atmospheres
above the temperatures due to the Sun’s heat
Jupiter has the largest internal source of heat
Most of it is probably primordial heat
18 July 2005
AST 2010: Chapter 10
19
Magnetic Fields
All four giant planets
have strong magnetic
fields
Their associated
magnetospheres are
large
They extend for millions of km in space
Jupiter’s field was discovered in the late 1950s
Radio waves were detected from Jupiter
They were produced by electrons circulating in its
magnetosphere by a process called synchrotron
emission
The magnetic fields of Saturn, Uranus, and
Neptune were discovered by flyby spacecraft
18 July 2005
AST 2010: Chapter 10
20
Atmospheres of Giant Planets
Only their atmospheres are directly observable
from space
They show dramatic examples of weather patterns
Storms on these planets can be larger in size than
the Earth!
18 July 2005
AST 2010: Chapter 10
21
Atmospheric Composition of Jovian Planets
Methane (CH4) and ammonia (NH3) were first
believed to be the primary constituents of the
atmospheres
We know today that hydrogen and helium are
actually the dominant gases
This was first shown by Voyager’s far-infrared
measurements by
There is less helium in Saturn’s atmosphere
The most precise measurements of composition
were made on Jupiter by Galileo’s entry probe
Since these planets have no solid surfaces,
their atmospheres are representative of their
general compositions
18 July 2005
AST 2010: Chapter 10
22
Clouds on Jovian Planets
Jupiter’s clouds are spectacular
ranging in color from white
to orange to red to brown
Movie
The explanation for the
colors remains a mystery
Saturn’s clouds are more “subdued” in color
They have nearly uniform butterscotch hue
18 July 2005
AST 2010: Chapter 10
23
Atmospheric Structure of Jovian Planets
18 July 2005
AST 2010: Chapter 10
24
Winds and Weather
The jovian planets’ atmospheres have many
regions of high and low pressure
Air flow between these regions sets up wind
patterns distorted by the fast rotation of the planet
The wind speeds are measurable by tracking cloud patterns
The weather patterns are different from Earth’s
Giant planets spin much faster than Earth
Rapid rotation smears out air circulation into horizontal
(east-west) patterns parallel to the equator
No solid surface
No friction or loss of energy – this is why tropical storms
on Earth eventually die out…
Internal heat contributes as much energy to the
atmosphere as sunlight (except for Uranus)
18 July 2005
AST 2010: Chapter 10
25
Winds on Giant Planets
Winds on Uranus and Neptune are rather
similar to those on Jupiter and Saturn
True on Uranus in spite of the 98O tilt
18 July 2005
AST 2010: Chapter 10
26
Giant Storms on Giant Planets
There are many storms on the giant planets
superimposed on the regular circulation patterns
The most prominent storms are large ovalshaped high-pressure regions on both Jupiter
and Neptune
The most famous is Jupiter’s Great Red Spot
in the southern hemisphere
30,000 km long (when
Voyager flew by)
present since first seen 300
years ago
changing in size, but never
disappearing
Movie
From Voyager 1 in 1979