Download Astronomy 1400 – 001: Solar System Astronomy

Astronomy 1400 – 001:
Solar System Astronomy
Lecture 33: The Jovian Systems
Friday, November 14, 2014
What is one way that planets do NOT lose their
atmospheres?
a)  condensation
b)  outgassing
c)  solar wind stripping
d)  thermal escape
e)  chemical reactions
What is one way that planets do NOT lose their
atmospheres?
a)  condensation
b)  outgassing
c)  solar wind stripping
d)  thermal escape
e)  chemical reactions
The Jovian (Jupiter-like) Gas Giant Planets
• 
• 
Jupiter and Saturn are more massive because they formed closer in (higher
density nebula)
At the distance of Uranus and Neptune, it is cold enough for molecular
compounds to form
-  Common: methane (CH ), ammonia (NH ), water (H O)
-  Less Common: acetylene (C H ), ethane (C H ), propane (C H )
4
3
2
2
2
2
6
3
8
Where do the colors come from?
•  Molecules
•  Saturn is duller
because the
atmosphere is
less
compressed…
How Spherical Are the Planets?
•  Sphericity depends on…
–  Gravity
–  Rotation rate (rotation periods
of outer planets are all less than
one Earth day—Jupiter and
Saturn are ~10 hours!)
–  Rigidness
•  Most spherical—inner planets
–  Earth = 0.7% difference
between equator and poles
•  Least spherical—outer planets
–  Saturn = 10% difference
between equator and poles
Atmospheric Structures
Jovian planets lose energy
____ than terrestrial planets
because they are ____
a) slower, less dense
b) faster, less dense
c) slower, larger
d) faster, larger
Jovian planets lose energy
____ than terrestrial planets
because they are ____
a) slower, less dense
b) faster, less dense
c) slower, larger
d) faster, larger
Jupiter is still so hot that it
emits twice as much energy
as it receives from the Sun!
Jupiter Has ≳3× the Mass of Saturn
Why is Jupiter Not a Lot Larger Than Saturn?
Clouds of Saturn
•  Saturn's layers are
similar, but deeper in
and farther from the
Sun (more subdued).
•  Gravity doesn’t tug
as hard (less
compressed than
Jupiter), so the lower
atmosphere is much
lower than Jupiter
➡  This is why you see
less cloud detail.
Jovian
Weather
• 
More rotation means more
cells from Coriolis force
and more wind
- 
• 
Earth’s hurricanes are pitiful
compared to Jupiter’s winds:
~250 mph!
Great Red Spot
- 
A big hurricane that has
existed for over 300 years
Clouds of Jupiter
white = cold (snowy)
dark = warm
Clouds of Uranus and Neptune
• 
• 
• 
All the jovian planets have strong winds and storms.
Great dark spot on Neptune only lasted ~6 yr
Uranus is more dull because of increased mixing of gases. Why might this
happen on Uranus (hint: what causes dust storms on Mars)?
Storms are starting to brew…seasons! (Uranus’s yr = 84 Earth yr)
➡ 
Temperatures of Jupiter’s Clouds
• 
The no greenhouse temperature of Jupiter:
280K 4 0.48
2
= 102K
5.2
➡  But the actual temperature is 124K
➡  How does the planet glow? blackbody
€
➡  How does the energy flux depend on temperature?
➡  Stephan-Boltzmann Law: the excess energy flux is
F ∝ T4 ~ (124 K / 102 K)4 ~ 2×
➡  Where does the excess energy come from?
Interior Structure
• 
• 
Internal heat from…
- 
Gravitational contraction
(Jupiter; ~1 inch/century)
- 
Differentiation (helium rain in
Saturn)
- 
Phase transition of hydrogen
Core sizes are ~10 MEarth
Magnetic Fields
• 
Magnetic field of Jupiter is
largest and strongest
- 
• 
~20,000× stronger than Earth’s!
Why? What does the
magnetic field size and
strength depend on?
- 
Amount of planet’s metallic
substances
‣ 
Metallic hydrogen
(Jupiter and Saturn only)
‣ 
Core metals
- 
Rotation rate
- 
Strength of solar wind
The Outer Planets Like
Mini Solar Systems
• 
Objects are bigger out there
because many more things (e.g.
water) can also condense
- 
• 
• 
e.g., Ganymede and Titan are larger
than Mercury!
Most moons formed out of the
accretion disks (only some were
captured)
- 
Revolve in the same direction as
planet’s rotation
- 
Smallest were probably captured
large asteroids/comets
How do moons rotate/revolve?
- 
Synchronously like the Moon
Runaway growth — extra condensing
materials made them big enough to accrete
hydrogen and helium
The Moons of the Outer Planets
How many moons are known in the solar system?
a) ~20
b) ~45
c) ~80
d) ~170
The Moons of the Outer Planets
How many moons are known in the solar system?
a) ~20
b) ~45
c) ~80
d) ~170
Io
The Most Volcanically Active Object in the Solar System
• 
No craters
• 
What does this mean?
➡  Very young surface
Io (Jupiter)
The Most Volcanically Active
Object in the Solar System
• 
Constant volcanic eruptions
• 
Supplies plasma for Jupiter’s aurorae
Why do the Volcanoes on Io
show up better in infrared
images?
a)  Because the infrared sees through clouds on Io
b)  Because they are hot, they appear brighter in the
infrared than the rest of Io
c)  Because they are not active volcanoes
d)  Because in the infrared image they are red
Why do the Volcanoes on Io
show up better in infrared
images?
a)  Because the infrared sees through clouds on Io
b)  Because they are hot, they appear brighter in the
infrared than the rest of Io
c)  Because they are not active volcanoes
d)  Because in the infrared image they are red
Where does the heat come from?
• 
- 
• 
Io should have cooled
by now. Why?
RIO ~ RMoon
Tidal heating
- 
From friction
- 
Strength ∝ 1/r3
- 
Affects Io the most because
it is closest to Jupiter
• 
But why is its orbit so
elliptical?
The amount of stretching is
highly exaggerated for clarity
Orbital Resonances
• 
Every 7 days, these
three moons line up
• 
The tugs add up
over time, making
all three orbits
elliptical.
What kind of resonance are the two moons below in?
A)  a 2:1 resonance
B)  a 3:1 resonance
C)  a 3:2 resonance
D)  a 4:1 resonance
E)  a 5:1 resonance
•  Finish Reading Chapter 11