ISP205 Lecture #14, Feburary 22, 2001
- Review: terrestrial Planets:
- Order of geological activity: (most active to least
active)
Earth, Venus, Mars, Mercury + Moon
- This can be explained with the different sizes
- Except Venus all terrestrial planets have older
highlands
and younger lowlands.
- Only Earth and Venus have active volcanoes.
Mars might have rare, occasional volcanic eruptions.
- Only Venus, Earth, and Mars have atmospheres
Venus: ~100 times thicker atmosphere than earth
made
mainly of CO2 and N2
Mars : ~100 times thinner atmosphere than earth
same
composition than Venus atmosphere
Earth: made mainly of N2 and O2
(modified
because of life on earth)
- The very different surface conditions on Venus, Earth,
and
Mars are a consequence of the different greenhouse effects.
- Only Mercury and Earth have a detectable magnetic
field.
- Water is found on Mercury, Earth, Moon, Mars but not
on Venus.
- Liquid water is only found on Earth.
- There are indications that Mars had liquid water in the
past.
- There are flow channels, mostly dating back to 3
billion years
(flowing water requires a thicker atmosphere to prevent rapid
evaporation - or an ice layer)
- There are hints of more recent floods
- The Giant Planets - Overview
(see picture of size comparison)
(see pictures of the giant planets)
Planet |
Size (1 = earth) |
Spin |
Orbit |
Axis tilt (degree) |
Jupiter |
11 |
10 hours |
12 years |
3.1 |
Saturn |
9.4 |
10 hours |
29 years |
27 |
Uranus |
4.0 |
17 hours |
84 years |
98 |
Neptun |
3.9 |
16 hours |
165 years |
29 |
- Whats inside ? The Galileo Mission to Jupiter
(Redshift demo of orbit)
(Picture sequence of Mission)
(Picture sequence of Mission results)
Going beyond the probe:
Distance from center |
Composition |
Temp. |
Pressure |
Probe destroyed |
|
426 K (153oC) |
22 bar |
59-71 Tkm |
H2,He gas/liquid |
|
|
|
|
11,000 K |
3 Mio bar |
14-59 Tkm |
metallic H |
|
|
|
|
25,000 K |
12 Mio bar |
7-14 Tkm |
"ice" (C,N,O + H) |
|
|
0-7 Tkm |
"rock" (Si, O, ...) |
|
|
center |
|
40,000 K |
50 Mio bar |
- Internal Composition of the Giant Planets - comparison
(picture from book)
- Jupiter
- Outer atmosphere: 86% H2, 14%He, traces of CH2, NH3
- Inner composition: metallic H, and small core of
ice, and rock
- Saturn
- Very similar to Jupiter, but much less Helium:
97%H, 3%He
- Explanation: He rained down towards center
(fractionation)
- Uranus
- Outer atmosphere: 83% H2, 15% He, 2% CH4
- Inner composition: Largely Ice and Rock
- Neptun
- Similar to Uranus - but somewhat more CH4: 3%
- Formation of the Giant Planets
- Why are the Giant Planets so different from the
terrestrial ones ?
- Temperatures in the outer solar system much lower
throughout
the history of the solar system. Therefore:
- Gravity of a terrestrial planet size object is
enough to bind
H and He (because molecule velocities are lower)
- Less solar wind (inverse square law) doesnt blow
gas away
- Hydrogen can be bound in molecules like CH4 and
NH2
that are stable at low temperatures and can form ice.
- Therefore outer planets could accumulate all H,He gas
that
was around.
- Initial composition of the solar system: 84% H and 16%
He !!
(see picture)
therefore giant planets can be much bigger than terrestrial ones
- Atmospheric activity
- All giant planets have high speed winds because of
rapid rotation
and no friction with a solid surface.
- Typical windspeeds are:
Jupiter: 200 m/s
Saturn: 300 m/s
Uranus: 200 m/s
Neptun: 600 m/s
- Spots are hurricanes reflecting tubulence, bands are
winds
in opposite directions for upward moving hotter gas and
downward moving cooler gas.
- Degree of Turbulence/ Band formation is very different:
- Jupiter has the most turbulent wheather with many
"hurricanes"
and pronounced bands.
(see pictures, movie)
- Saturn shows sometimes hurricanes in summer (every
30 years)
and some band structure
- Neptun had hurricanes in 1986 (Dark spot) but not
in 1994 anymore
shows some band structure
- Uranus shows no signs of turbulence or bands
- Turbulence/ Band formation requires:
- rapid rotation
- internal heat source that triggers convective motion
perpendicular
to rotation
- Jupiter, Saturn have a strong internal heat sources
- Neptun has a small internal heat source
- Uranus has no internal heat source
- Possible heat sources are:
- Primordial heat leftover from formation
(Jupiter)
- Ongoing contraction
- He fractionation (Saturn - see low He in
atmosphere)
- Magnetic fields
- Magnetic field formation requires rotation and a
liquid, conducting
core
- All giant planets have strong magnetic fields, but only
Jupiter and
Saturn have a liquid, conducting core of metallic hydrogen.
- The origin of the magnetic fields of Uranus and Neptun
is unknown