Gas Giants"): The Giant Planets - Jupiter, Saturn, Uranus, Neptune
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Chapter 8
The Giant Planets
(“Gas Giants”):
Jupiter, Saturn, Uranus, Neptune
Called giant planets because of their mass:
from 15 Earth masses (Uranus/Neptune)
to
318 (Jupiter)—and also, their physical size.
URANUS
NEPTUNE
The ancient sky +1500 years = heliocentric system
(geocentric system)
5 planets & Sun 6 planets
& &
Earth Sun
Copernicus 1543
+ 124 years Tycho 1571
Still 6 planets Kepler 1596
Galileo 1589
Newton 1667
But we are so much smarter!!!!
{ }
Descarte
+ 67 years Kant Nebular Theory (1734)
Laplace
Still 6 planets
Now we are even more smarter AND we have a plan !
+ 47 years 7 planets (Uranus is discovered, 1781)
+ 65 years 8 planets (Neptune is discovered,1846)
+ 83 years 9 planets (Pluto is discovered, 1929)
+ 61 years 10 planets ( planet around pulsar
(PSR B1257+12) is discovered,1990)
+ 5 year 11 planets (planet around 51 Peg is
discovered, 1995)
+ 10 years 161 planets (150 gas giant planets are
confirmed, 2005)
+ 1 year 160 planets (Pluto reclassified to a dwarf
planet, 2006)
+ 7 years 760 planets are confirmed, 2012 !!!!!
! Jupiter and Saturn: easily seen by eye. ! Large, cold, and massive. ! Jupiter and Saturn are primarily hydrogen and helium—gas giants. ! Uranus and Neptune contain much more water ice and other ices—ice giants. ! No solid surfaces: we just see the cloud layers in the atmospheres.
rotation period (hrs) 9.94 10.56 17.23 16.10
Are jovian planets all alike?
Yes No
Same solid mass J & S have huge gas env
Have rings U & N are smaller than J & S
Have many moons Mostly hydrogen compounds:
Mostly H & He (H2O), methane, ammonia
Some H, He, and rockGas giants must form before the solar nebula dissipates
(< 3 to 5 million years)
Disks are seen around many young starsFormation of the gas giant planets via core accretion
This means accumulating gases (H and He) from the
solar nebula.
Ice was an abundant core-building material > 5 AU from
the Sun.
Inside the frost line: Too hot for H
compounds
to form ices.
Outside the frost line: Cold enough for
ices to form.Comparative Planetology
as we used for terrestrials
1. Formation history
2. Interior
geological activity
3. Atmosphere
atmospheric activity
4. Magnetic field
magnetic field activity
Can we use this for the gas/ice giants?Comparative Planetology
as we used for terrestrials
1. Formation history ---> core accretion
2. Interior
Then what?
geological activity
3. Atmosphere
atmospheric activity Are there atmospheres?
4. Magnetic field
magnetic field activity Oh yes!
Can we use this for the gas/ice giants?Comparative Planetology
Jupiter Saturn Uranus Neptune
General properties
Interior
Atmosphere
bands
Red Spot/Storm
Magnetic Field
Moons
How do we study Gas Giant Planets ?
Not particularly easy to get there …
And not easy to get on to the planets !
Laws of physics and chemistry + observations = model for giant planetsInteriors
Neptune Uranus
Jupiter
SaturnMagnetic Fields
General Shape
Gas giants rotate differentially:
rotation is faster at their equator than their poles
Jupiter is the most rapidly
rotating planet in the Solar
System:
Rotation period slightly
less than 10 hr.
Jovian planets are
not quite spherical
because of their
rapid rotation
oblate shapeContains almost 3/4 Largest and most
of all planetary massive planet in
matter in the solar the solar system
system.
Explored in detail
by several space
probes:
Pioneer 10,
Pioneer 11,
Voyager 1,
5/5
Voyager 2,
GalileoThe Mass of Jupiter Using Kepler’s third law → MJupiter = 318 MEarth Mass can be inferred from the orbit of Io, the innermost of the 4 Galilean Moons:
Jupiter’s Interior
The layers are different for the different planets. WHY?
• High pressures inside Jupiter cause phase of
hydrogen to change with depth
• Hydrogen acts like a metal at great depths
because its electrons move freely• Jupiter/Saturn: at depths of a few 1,000 km,
gases are compressed so much they liquefy.
– At higher pressure and temperature, this liquid
hydrogen can act like a metal.
• Cores are liquid rock and water.• Uranus/Neptune:
– Have much less hydrogen and helium.
– Have more water and ices (ammonia, methane).
– Cores took longer to form.
http://www.huffingtonpost.com/2013/08/11/crab-methane-video_n_3739602.html
Interesting visual about methaneJupiter’s Interior Phase diagram for water
Jupiter’s Interior
Hydrogen phase diagram
• Jupiter – interior mostly metallic hydrogen
• Saturn – some metallic hydrogen
• Uranus/Neptune – molecular hydrogen onlyNeptune Uranus
Got weather?
Storms on all 4 gas giant planets
Jupiter
SaturnThe Great Red Spot on Jupiter
Has been visible for over 330 years.
Formed by rising gas carrying
heat from below the clouds,
creating a vast, rotating storm.
White oval: 40 year old storm,
about the size of Earth
~ 2 DEarthThe Cloud Belts on Jupiter
Just like on Earth, high-and low-pressure zones
are bounded by high-pressure winds.
Jupiter’s Cloud belt structure has remained unchanged
since humans began mapping them.Jupiter’s Atmosphere: Clouds
Three layers
of clouds:
1. Ammonia
(NH3) crystals
2. Ammonia
hydrosulfide
3. Water
crystalsJupiter contains hydrogen, helium, water (H2O), ammonia (NH3) methane (CH4)
What causes the cloud bands on Jupiter?
(dark Belts and bright Zones)
Strong winds and Jupiter’s differential rotation produce bands
parallel to equator The giant planets all have magnetic fields, rapid rotation & atmospheres, so we expect them to have aurorae too! ~ 1000 times more powerful than aurorae on Earth.
• Magnetic fields are generated by the motion of the electrically conducting liquids. • Their orientation is at an angle to the rotation axis. • Like bar magnets.
Jupiter’s Magnetic Field
Discovered through observations of decimeter (radio) radiation
Magnetic field at least
10 times stronger
than Earth’s magnetic
field.
Magnetosphere over
100 times larger than
Earth’s.
Extremely intense
radiation belts:
Very high energy
particles can be
trapped; radiation
doses corresponding
to ~ 100 times lethal
doses for humans!The giant planets have strong magnetic fields!
“Io flux tube”
A million
amps of
current
flowing
between Io
and Jupiter
Aurorae on
Jupiter (they
occur on all the
outer planets)Jovian Ring Systems • All four jovian planets have ring systems • Saturn’s rings are extensive; others have smaller, darker ring particles
Jupiter’s Ring
Composed of microscopic particles of rocky material
Galileo spacecraft image of Jupiter’s ring, illuminated from behind
Voyager spacecraft discovered Jupiter’s rings in 1980 !!
Search was on for Uranus’ ring system!Jupiter’s Ring Ring material can’t be old because radiation pressure and Jupiter’s magnetic field force dust particles to spiral down into the planet. Rings must be constantly re-supplied with new dust.
GETTING HIT
http://
georgeastro.w
eebly.com/
http://
jupiter.html
cosmiclog.nbcnews.com/ http://www.space.com/
_news/ 17535-latest-explosion-on-
2012/09/10/13789057- jupiter-captured-by-
flash-spotted-on-jupiter-is- amateur-astronomer-
it-a-hit?lite video.htmlComet Impact on Jupiter
Impact of 21 fragments of comet SL-9 in 1994
Impacts occurred just behind the horizon as seen from
Earth, but came into view about 15 min. later.
Impact sites appeared very bright in the infrared.
Impacts released energies equivalent to a few megatons of TNT
(Hiroshima bomb: ~ 0.15 megaton)!
Visual: Impacts seen for many days as dark spotsin 1993, a comet was discovered to be on a collision course with Jupiter
Our view Galileo satelliteImpact of 21 fragments of comet SL-9 in 1994
July 16,1994
5/7
Cassini Spacecraft View of Saturn
11/28Saturn’s Ring system, by Cassini
• Mass: ~ 1/3 of mass of Jupiter
• Av. density: 0.69 g/cm3 → Would float in water!
• Rotates about as fast as Jupiter, but is twice as oblate
• No large core of heavy elements (liquid H core)
• Saturn radiates ~ 1.8 times the energy received from the Sun.
Probably heated by liquid helium droplets falling towards center.
Pioneer 11 (1979)
Voyager I & II (1980-81)
Cassini (2004)Atmosphere
• 92.4% molecular hydrogen
• 7.4% helium
* missing helium (compare to Jupiter)
* sank toward center (differentiation)?
• 0.2% methane
• 0.02% ammonia
• little of the early atmosphere escaped due to the strong
gravity (large escape velocity)
Pioneer 11 (1979)
Voyager I & II (1980-81)
Cassini (2004)Saturn’s Rings
Perfect example of a planet’s ring system.
Are Saturn’s rings the
norm?
How do these
compare to rings of
other jovians?Jovian Ring Systems
• All four gas giants have ring systems. • Composed of countless tiny particles. • Ring particles obey Kepler’s laws. • Particles most likely came from moons disrupted by tidal stresses.
Saturn’s Rings
Rings could not have
been formed same time
as Saturn because
material would have
been blown away by
particle stream from hot
Saturn at time of
formation.(167,777 mi; 33 ft)
Jovian Planet Rings What are they? Where did they come from? How did they form? Why do the jovian planets have rings? Looking closer at Saturn’s rings!
Composition of Saturn’s Rings
Rings are
composed of
ice particles
They orbit
over Saturn’s
equator
They are very
thin• Saturn has the most complex rings. • A very complicated system, composed of thousands of ringlets. • There are bright and dark rings, “gaps,” and divisions. • Gaps are not empty. • Brightness/darkness reflects the amount of material in each ring. • Though wide, the ring system is extremely thin.
The Roche Limit: the critical distance inside which a large moon will be pulled apart by tidal forces
Rings are always inside the Roche limit, large moons are always outside
Gap Moons
• Some small
moons create
gaps within ringsShepherd Moons • Pair of small moons can force particles into a narrow ring
Shepherd Moons Pair of small moons can force particles into a narrow ring
Resonance Gaps
• Orbital resonance
with a larger moon
can also produce
a gapResonance Gaps
Ring Formation • Impacts on these moons are random
Ring Formation
Ring Formation
saturn http://vimeo.com/40234826
Jovian Planet Atmospheres
Other jovian planets
have cloud layers
that are similar to
Jupiter’s and
formed the same
way but not as
distinct as on
Jupiter; colder than
on Jupiter.
Different compounds
make clouds of
different colorsClouds: * Three layers * Thicker than Jupiter - blocking view into different layers ( explanation for bland appearance of Saturn's surface
http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20111117/
on Dec. 5, 2010, through its subsequent growth into a storm so large it completely encircled the planet by late January 2011. The monster tempest, which extended north-south approximately 9,000 miles (15,000 kilometers), is the largest seen on Saturn in the past two decades and is the largest by far ever observed on the planet from an interplanetary spacecraft. The storm's 200-day active period also makes it the longest-lasting planet- encircling storm ever seen on Saturn. The previous record holder was an outburst sighted in 1903, which lingered for 150 days. "The Saturn storm is more like a volcano than a terrestrial weather system," said Andrew Ingersoll, a Cassini imaging team member at the California Institute of Technology in Pasadena. "The pressure builds up for many years before the storm erupts. The mystery is that there's no rock to resist the pressure – to delay the eruption for so many years."
Saturn’s Internal Structure
• Jupiter/Saturn: at depths of a few 1,000 km, gases are
compressed so much they liquefy.
– At higher pressure and temperature, this liquid hydrogen
can act like a metal.
• Uranus/Neptune:
– Have much less hydrogen and helium.
– Have more water and ices (ammonia, methane).
– Cores took longer to form.Saturn’s Magnetosphere
Magnetic field ~ 20 times weaker than Jupiter’s
Aurorae centered
around poles of
rotationOther Magnetospheres
All the jovian planets
have substantial
magnetospheres,
but Jupiter’s is
largest by farOther Magnetospheres
All the jovian planets
have substantial
magnetospheres,
but Jupiter’s is
largest by farSaturn’s Magnetosphere
Magnetic field ~ 20 times weaker than Jupiter’s
Aurorae centered
around poles of
rotationThe Roche Limit: the critical distance inside which a large moon will be pulled apart by tidal forces
The Rings of Uranus
Rings of Uranus and Neptune are similar to Jupiter’s.
Confined by shepherd moons; consist of dark material.
Apparent motion of Rings of Uranus were
star behind Uranus discovered through
and rings
occultations of a
background starThe Rings of Neptune
Focused by small
shepherd moons
embedded in the ring
structure.
Made of dark
material, visible
in forward-
scattered light.• The other giants’ rings are mostly narrow and diffuse. • Backlighting brings them into view. • Neptune has denser sections known as ring arcs.
End of Chapter 8
Giant Planets of the Solar System
Now you know general
characteristics of the
Giant PlanetsYou can also read
