Download Chapter 11 The Jovian Planets

Chapter 11 The Jovian Planets
•The Jovian planets: Jupiter,
Saturn, Uranus and Neptune
• Using Venus transit it was possible to get a
good value of the AU (1639). Knowing the
AU, it is possible to calculate the size of the
planets. Their physical size can be
calculated using their angular size and the
distance
Physical size = angular size x (2 π x distance)/360
(Read textbook page 30)
Once the distances have been determined it is possible to calculate the orbital radius of the
satellites. The mass of the planets can be calculated by measuring the orbital radius and the
orbital period of the satellites (and using Newton’s modified 3 rd Kepler law)
Knowing the mass and diameter, allows to calculate the densities, proving that the Jovian
planets are very different from the terrestrial planets
•The Jovian planets: Jupiter,
Saturn, Uranus and Neptune
•Their masses are large compared with
terrestrial planets, from 17 to 320 times
the Earth’s mass
•They are gaseous
•Low density
•All of them have rings
•All have many satellites
•All that we see of these planets are the
top of the clouds
•No solid surface is visible
•The density increases toward the
interior of the planet
•All of them located a larger distances
from the Sun, beyond the orbit of Mars
The
Jovian
Planets
Jupiter
•Named after the most powerful Roman
god
• It is the third-brightest object in the
night sky (after the Moon and Venus)
•It is the largest of the planets
•Atmospheric cloud bands - different
than terrestrial planets
•The image shows the Great Red spot, a
feature that has been present since it
was first seen with a telescope more
than 350 years ago
Distance from Sun: 5.2 AU
Diameter: 11 diameter of Earth
Mass: 318 mass of Earth
Density: 1,3 g/cm^3
Escape velocity: 60 m/s
Surface temperature: 120 K
Composition: mostly H and He
•Many satellites , about 66.
•The four largest are called Galilean
satellites. Discovered by Galileo in
1610
•A faint system of rings. Too faint to
see them with ground -based telescopes
Saturn
• The second largest planet
•Visible with the naked eye
•Named after the father of Jupiter
• Almost twice Jupiter’s distance from
the Sun
• Similar banded atmosphere
• Uniform butterscotch hue
• Many satellites. The largest is Titan,
the only satellite to have a permanent
atmosphere
• Spectacular ring system seen with
even small telescopes
•This was the last planet know to the
ancients
Distance from Sun: 9.24 AU
Diameter: 9.5 Earth diameter
Mass: 95 Earth mass
Density: 0.71 g/cm^3
Escape velocity: 36 km/s
Surface temperature: 97 K
Composition: mostly H and He
Uranus
• Discovered by William Herschel in
Distance from Sun: 19.2 AU
Diameter: 4.0 Earth diameter
Mass: 14 mass of Earth
Density: 1.24 g/cm^3
Escape velocity: 21 m/s
Surface temperature: 58 K
Composition: H compounds, H,
1781
• Named after the father of Saturn
• Barely visible to naked eye, even
under dark skies
• Featureless atmosphere
•Green, bluish color due to presence of
methane in the atmosphere
•Methane absorb the red part of the
spectrum and reflect the blue
• It showed small deviations in the
expected orbit.
•Was another planet influencing its
motion?
• The deviation led to the discovery of
Neptune
•Faint ring system not visible with
ground-based telescopes
Neptune
• This is the other planet whose
gravitational pull is influencing the orbit
of Uranus
• It’s mass and orbit were determined
first , in 1845 by the English John
Adams and a bit later by the French
astronomer Urbain Leverrier
• In 1846 it was discovered by the
German astronomer Johann Galle
• Too faint, cannot be seen with naked
eye
• It has a bluish color due to the
presence of methane in the atmosphere
•Faint ring system, not visible with
ground-based telescopes
Distance from Sun: 30.1 AU
Diameter: 3.9 Earth diameter
Mass: 17 Earth mass
Density: 1.67 g/cm^3
Escape velocity: 24 km/s
Surface temperature: 59 K
Spacecraft Exploration of Jovian Planets
•Pioneer 10 and 11. Reached Jupiter around 1973
•Voyager 1and 2 left Earth in 1977
•Reached Jupiter in March and July of 1979
• Used Jupiter’s strong gravity to send them on to Saturn - gravity assist
• Voyager 2 used Saturn’s gravity to propel it to Uranus and then on to Neptune
• Studied planetary magnetic fields and analyzed multi-wavelength radiation
• Both are now headed out into interstellar space!
Space Craft Exploration of Jovian
Planets, more recent missions
• Galileo - launched in 1989 and reached
Jupiter in December 1995
• Gravity assists from Venus and Earth
• Spacecraft has two components:
atmospheric probe and orbiter
• Probe descended into Jupiter’s atmosphere
• Orbiter entered orbit, went through moon
system
•Juno mission: On it way to Jupiter.
Scheduled to arrive at Jupiter in July 2016
• Cassini mission to Saturn arrived June 30, 2004
• It consist of the orbiter and the Huygens probe
•Orbiter will orbit Saturn and its moons for 4 years (at the present it
is active and returning data)
• Huygens probe launched from the orbiter. Descended on Titan
January 14, 2005 to study Saturn’s moon .
The mass-radius dependence for a H and He
planet
Notice that
Jupiter is
slightly larger
than Saturn even
if it is about 3
times more
massive
Adding more
mass, compress
the planet
increasing its
density but not
its size
Distortion of Jovian planets due to fast
rotation
Rapid rotation creates
a bulge around the
equator.
The shape departs
from a perfect sphere
•Saturn is distorted,
10% larger at equator
•Jupiter shape is also
distorted, about 7%
larger at equator.
Caused by fast
rotation, large radius
Jupiter’s Interior
(And Earth for comparison)
• Metallic hydrogen is a
superconductor. A
superconductor conduct
electricity with minimum or
no resistance
Jovian planets interiors
There is no data on direct measurements of the interior of the Jovian
planets
The structure of the interior of the Jovian planets is obtained through
modeling based on the composition and the mass
Jupiter’s Atmosphere
Characterized by two main features: Colored bands
(zones and belts) and the Great Red Spot
Atmospheric content:
• molecular hydrogen – 86%
• helium – 14%
• small amounts of methane, ammonia, and water vapor
•The Great Red Spot seems to be a hurricane that has
lasted for more than 350 years
•The bands are caused by convections and high wind
velocity at the top of the clouds
•Darker belts lie atop downward moving convective
cells
•Lighter zones are above upward moving cells
•Belts are low-pressure, zones are high pressure
•Jupiter’s rapid rotation causes wind patterns to move
East/West along equator
•The color of the bands may be due to the presence of
trace elements sulfur and phosphorus and compounds
of molecules of these elements
•The formation of these molecules is sensitive to
temperature and that may account for the different
colors of Belts and Zones
Weather on Jupiter
Main weather feature : Great Red Spot!
• Swirling hurricane winds
• Has lasted for more than 350 years!
• Diameter twice that of Earth
• Rotates with planet’s interior
• The spot appears to be confined and
powered by the zonal flow. Not much
change in the latitude of the Great Red
Spot
Smaller storms look like white ovals (this one is over 40 years old)
Why do the storms last so long?
On Earth, hurricanes loose power when then come upon land
No solid surface on Jupiter, just gas. Nothing to stop them once they start
Temperature profile of Jovian planets
Jovian planets
- The axis tilt and magnetic fields
•All Jovian planets (and the Earth) have strong magnetic fields . They are caused by
the rapid rotation and liquid conductive cores or mantles.
•All of them emit low frequency radio emission. The emission is caused by the
interaction of electrons with the magnetic field
•The magnetic fields are offset from the center and have different tilt respect to the
rotational axis
•Uranus has the most inclined rotational axis: It has extreme seasons!
Jupiter’s Magnetosphere
Auroral emission
Jupiter magnetic field and the low frequency emission
Jupiter has the strongest magnetic field of all the planets
•Jupiter produces strong radio
emission at short wavelength
or low frequencies (Less than
39 MHz)
•The radio emission is
generated by electrons
accelerated in the magnetic
field lines connecting Io and
the Jupiter
•This radio emission can be
received with a simple antenna
•Two types of radio emission
are common: L (long) bursts
and S (Short) bursts
Jovian Magnetospheres
•All the Jovian planets have relatively
strong magnetic fields
•All emit low frequency radio emission
•Jupiter has the strongest magnetic
field
• Jupiter emit low and high frequency
emission (two different mechanisms)
• The cutoff of Jupiter low frequency
radio emission is around 40 MHz, the
highest frequency of all the planets.
•It is the only planet from which we
can receive the low frequency emission
in ground-based radio telescopes
•The rest of the Jovian planets emit
low radio emission but it cannot be
received in ground-based radio
telescopes. The frequency is too low
and cannot propagate through the
Weather on Saturn
•Computer enhanced image shows bands, oval storm systems, and turbulent
flow patterns like those seen on Jupiter
•The colors in the image are not the natural colors of Saturn
The Atmospheres of Uranus and Neptune
The atmospheric content:
•molecular hydrogen 84%
•helium 14%
•methane 2% (Uranus) 3% (Neptune)
Abundance of methane gives these planets their blue color
Methane absorbs longer wavelength light (red) and reflects short
wavelength light (blue)
Uranus and Neptune bluish color and presence of methane in
their atmospheres
Weather on Uranus and Neptune
Uranus
•Few clouds in the cold upper atmosphere – featureless
•Upper layer of haze blocks out the lower, warmer clouds
Neptune
•Upper atmosphere is slightly warmer
than Uranus (despite its further distance
from Sun)
•More visible features (thinner haze, less
dense clouds lie higher)
•Storms – Great Dark Spot
•Seen in 1989 (Images taken by Voyager
spacecraft) – gone in 1996 (Hubble
telescope)
A Summary of the Jovian Planet Properties
•Most of their mass is Hydrogen and Helium – light elements = low densities
•High surface gravity allows their atmospheres to retain these light elements
•Dense compact core at the center
•No SOLID surface –The gaseous atmosphere becomes denser (eventually liquid) at
core
•Differential Rotation – outer regions rotate at a different rate than the inner regions
The moons or satellites of the Jovian planets
Jovian Planet Moons
•There are:
•Six large moons, similar in size to our Moon
•12 medium-sized - 400 to 1500km
•Many small moons
•Jupiter - 67 moons
•Saturn - 62 moons
•Uranus - 27 moons
•Neptune - 13 moons
Jupiter’s Galilean satellites:
•Io - Jupiter’s moon with active
volcanoes!
•Europa - Jupiter’s moon covered
with frozen water - possible an
ocean of liquid water beneath
•Ganymede and Callisto - similar
in size to our moon, a bit larger.
•Ganymede is the largest moon in
the solar system
Four largest Jupiter moons - Galilean Moons
Jupiter
Saturn
Uranus
Neptune
Medium &
large moons
• All these moons have
enough self-gravity to be
spherical
• Some are now or were in
the past geologically active.
• Most of them have
substantial amounts of ice.
Jupiter’s “Galilean Moons”
An Unusual Family
Moon
Io
Europa
Ganymede
Callisto
What makes Jupiter’s Galilean moons unusual?
• Io has several active volcanoes.
• Europa may have an ocean of liquid water under
its ice.
• Ganymede & Callisto may also have sub-surface
oceans?
How can we account for the unusual
features?
Shouldn’t they be cold & dead?
Io’s Volcanoes
•
•
•
•
•
•
•
So far about 80 active
volcanoes have been
identified using data mainly
from Voyager and Galileo
spacecrafts
Volcanic eruptions mainly
composed of sulfur & sulfur
dioxide
Volcanic plumes about 150
km high and 300 km wide
Variety of volcanic hot spots
Large lava lakes made of
liquid sulfur
Tidal heating provides the
source of volcanic activity.
Io orbit is elliptical.
Compressing and stretching
of Io release heat.
Io: Two images separated by 15 years
A better view of Io’s volcanoes
Tidal Heating
Io is squished and stretched as it orbits
Jupiter . This releases of heat and rises
the internal temperature
Why is its orbit so
elliptical?
The Jovian Moons
Orbital resonance between the orbital periods of Io,
Europa and Ganymede
The 3 closest moons line up every 7 Earth days (resonance)
Tugging in the same direction distorts the orbit from a circle to an ellipse
1 orbit of Ganymede = 2 orbits of Europa = 4 orbits of Io
Smooth Europa
• Icy surface covering a
large rocky core:
– Surface is very smooth &
young.
– Fractured into ice rafts &
floes a few kilometers
across,
– Repaved by water or
geysers through the cracks
in the ice.
Europa
• Surface is ice covered
• Extensive & complex network
of cracks in icy crust
– internal geologic activity
Europa (200km square)
Europa
• Salt water oceans below thick layer of ice?
(Calculations show it may have twice as
much water as Earth!!)
• Mostly salt water, some magnesium
sulfate, sulfurs (red color)
Does Europa have liquid water?
What lies beneath Europa’s
surface?
One possibility:
– 100-200 km of convective ice
above a rocky core
The most probably scenario
based on measurement of
Europa’s magnetic field:
– Thin ice crust a few km thick
over a 100 km deep water
ocean.
Europa
How Europa can maintain liquid water?
•Heat in the interior come from interaction
(tidal heating) with Jupiter and distortion
of the orbit (elliptical) by interaction with
nearby satellites
•Thermal vents may bring the heat from
the core.
•Heat may keep the interior temperature
above freezing point
Possibility of life?
• The existence of liquid water does not
imply the emergence of life. The salty
water is a hostile environment. But we
have seen on Earth that life can be present
in environment that were considered
hostile
Tidal stresses crack Europa’s surface ice. Similar to
icebergs, large chunks of ice that have been broken and
reassembled
•Titan, Saturn largest satellite
Titan is the only satellite in the solar system to
have an atmosphere. It has a methane-ammonia
atmosphere
It was recently visited by Cassini (at the present in
orbit around the planet) and the Huygens probe.
Rocky surface and evidence of erosion by
liquid/slush.
Titan
•Properties:
– Mass: ~0.02
Earth-mass
– Radius: 0.4 REarth
– Density: ~1.9
g/cm^3
– Icy mantle over a
rocky core.
• This is the only
satellite (moon) in the
solar system that has
heavy atmosphere
Titan’s Atmosphere
•Composition:
–
–
–
–
~80% N2 (nitrogen)
~3% CH4 (methane)
Argon
Hydrocarbons like:
•
•
•
•
Ethane = C2H6
Acetylene = C2H2
Ethylene = C2H6
Propane = C3H8
– Clouds of methane & N2 ices
The Huygens probe
The Huygens lander was carried by
the Cassini spacecraft mission .
The image to the right is an image
from the surface of Titan returned by
the Huygens probe
The methane/ethane lakes in Titan.
Radar images taken by Cassini
Lakes on Titan (radar maps)
Titan’s Liquid Lakes
Cassini radar have been
able to image several
smooth regions that have
been identified as lakes of
liquid methane/ethane
Titan, a reflection of sunlight in a methane/ethane
lake.
(Image taken by Cassini spacecraft)
Titan interior
Saturn satellite Mimas and Star
Wars’ Death Star
Triton
Triton - Neptune’s large
moon
•It has a retrograde orbit . It orbit in
direction opposite to Neptune
rotation
•Voyager 2 detected geysers of
nitrogen gas rising several km high
• The gas jets of nitrogen comes
from liquid nitrogen heated by some
internal source of heat
•A very thin atmosphere of nitrogen
•Temperature about 37 K
The Jovian Planets rings
Rings
All of the Jovian planets
have rings
The most spectacular are
Saturn’s rings
•They are very thin, less
than a few km
•Rings are not solid objects
• They are comprised of
many small solid particles
•All the particles are in
orbit around the planet
•Water ice is the primary
constituent
Why do rings form?
Tidal forces (differential gravitational
forces) of the large planet can break apart
a close enough moon.
Rings
• Rings consist of billions of
small particles or moonlets
orbiting close to their planet
– size of particle ranges from
grain of sand to housesized boulders
Rings
• Particles follow Kepler’s laws
– inner particles revolve faster than
those farther out
– ring are not rotating, rather
individual moonlets revolving
• if ring particles widely spaced move independently
• if particles are close gravitationally interact
• moons clear gaps in rings
Saturn’s ring in false colors to enhance the
composition
Saturn rings, gaps and shepherding moons
Origin of Rings
• Breakup of shattered satellite
• Remains of particles that were
unable to come together and form
satellite
• Gravity plays important role
– differential force of gravity -tidal forces
• tear bodies apart
• inhibit loose particles from
coming together
DFg
DFg
DFg
Roche Limit
• Roche Limit - the closest distance an object can come to another
object without being pulled apart by tidal forces
Comparing Jovian Ring Systems
•
•
•
•
Compared to Saturn, the ring
system of other Jovian planets:
• have fewer particles
• are smaller in extent
• have darker particles
The rings of Uranus were
discovered in 1977 when the planet
passed in front of a star and the
rings dimmed the light from the star
The rings of Jupiter and Neptune
were discovered by the Voyager
spacecrafts
Other unsolved mysteries:
• Uranus’ rings are eccentric and
slightly tilted from its
equatorial plane.
• Neptune has partial rings.
Jovian Rings
An example: Comet Shoemaker-Levy 9.
It broke into 23 pieces after coming inside the Roche limit of
Jupiter in 1993
Collided with Jupiter in July 1994
Comet S-L 9
The string of pieces of the comet on their way to
Jupiter