ISP205 Lecture #15, Feburary 27, 2001
- Announcements
- New feature on the Web Site: Quiz Answers
- Bonuspoint Project #2 available on web site
Due: March 18
- Special Bonuspoint Project #3 will be opened after
spring
break: Write about an astronomy related experience
during spring break.
Rules:
- One brief paragraph is sufficient
- PG-13 max !
- Good for 2 special Joker Bonuspoints
(can be applied to anything)
- There will be a vote for the best story
2 best stories obtain another 4 points each
- Review Giant Planets
- Giant Planets have no surface as terrestrial planets,
but
have a huge atmosphere and a liquid and solid core.
- Very fast winds in the atmosphere, because of rapid
rotation and no surface where friction could slow them.
- "Surface" features formed by winds:
- Zones and Belts are bands where convection moves
gas upward or downward respectively
- Winds in zones and belts go in opposite directions
- Spots are "Hurricanes" forming around
high pressure
regions (Turbulence) at interface of opposite wind
streams.
(see picture)
- Giant Planets formed in colder region of solar system:
Ices (CH2, H2O, ...) and light gases (H, He) can be used to built a
planet and are the main constituents
- Giant Planets spin fast (10-17 hours) but orbit slow
- Jupiter:
- Very active atmosphere: permanent spots
("great red spot")
pronounced zones and belts, lots of turbulence.
- Strong internal heat source, probably primordial
heat
from formation.
- Very strong magnetic field (100 x earth)
- Composition: H, He atmosphere, liquid metallic H
ocean,
some ices, "small" rocky core
- 3 cloud layers, top layer are Ammonia clouds (most
visible)
- Hear Jupiter
- Saturn:
- Atmosphere shows zones and belts, but spots only
temporarily during summer
- Internal heat source, probably He raining from
atmosphere
into core (Atmosphere is He depleted!)
- Strong magnetic field (comparable to earth)
- Composition and cloud layers similar to Jupiter
- Uranus:
- No atmospheric activity visible
- No internal heat source
- Strong magnetic field (comparable to earth)
- Composition: H,He,CH2 atmosphere, large amounts of
ice and "small" rocky core.
- Ammonia cloud layer missing - condensed into snow
Therefore darker, blueish surface compared to Jupiter/Saturn
- Uranus spins on its side - strongest seasons in the
solar
system.
- Neptune:
- Showed some atmospheric turbulence in 1986
(Voyager)
(spots, scooter), but not today
- Internal heat source (contraction ?)
- Very strong magnetic field
- Composition similar to Uranus
- Record wind speeds in solar system: 1350 mph
(supersonic winds)
- Pluto:
- Discovery of Neptune
- Predicted to exist by mathematicians John Adams,
and Urbain Leverrier 1854,1846.
(they determined size and position from deviations of
Uranus orbit from Keplers Laws)
- Found by Johan Galle in 1846
- Discovery of Pluto
- Parcival Lowell calculated Plutos size and position
from remaining, unexplained deviations in Uranus
orbit - but deviations were not real !
- 1929 (13 years after Lowells death) search resumed
at Lowells observatory.
- 1930 Clyde Tombaugh discovered Pluto after
comparing
hundreds of photographs (each with 160,000 stars).
(picture of discovery)
- Plutos/Charons properties:
- Pluto: 2200 km diameter (half of Mercury)
- Orbits in 249 years and spins in 6.4 days, but
spins "on its side" similar to Uranus
- Pluto has a moon: Charon
1200 km diameter (biggest moon in solar system compared
to its planet)
- Charon was discovered 1978 by James Christy from
distortions in Plutos position (but not resolved)
In 1987 Pluto and Charon were in occultation (Demo)
and orbit/sizes could be measured (happens only every
124 years !)
(see HST movie)
- Charon and Pluto are tidally locked (orbit AND
spin)
seen from Pluto the Moon doesn't move or spin at all
(angular size of Charon: 3.5 degrees )
what about moon phases ?
- Density: 2.1 g/cm2 - probably mixture of rock and water
ice
- Surface temperature 50K (farthest from sun) to 60K
(summer)
Pluto also spins on its side - so summer lasts 124 years !
- Frozen surface, mainly water ice
- During summer a thin atmosphere of evaporated N2
(97%)
and some CH2
- Origin: maybe a previous member of the Kuiper belt that
accumulated material in collisions. Later collision formed
Charon and explains tilted orbit and spin.
This would mean that Pluto is not really a planet !
- Moons of the Giant planets
- Moon count:
|
Book |
end of 2000 |
Jupiter |
16 |
28 |
Saturn |
19 |
22 |
Uranus |
18 |
21 |
Neptune |
8 |
|
Most new discovered moons are about 1-10 km large
- There are regular and irregular moons:
regular moons: counter clockwise orbit (seen from north),
not very eccentric, in
equatorial plane
irregular moons: "retrograde" clockwise orbit, highly
eccentric,
inclination out of equatorial
plane
- Example: Jupiter has 8 regular moons, and 20 irregulars
Redshift Demo
- 23 moons are larger than 200 km:
(see picture)
(discuss 6 largest)
- Triton (Neptune moon) (picture)
- Size: 80% of earth's moon
- Composition (and distance from sun) very similar
to Pluto - related ?
- Lowest surface temperatures measured in the solar
system:
35-40 K, because high reflectivity (ice surface)
- Few impact craters - lots of geological activity ?
Cyro-vulcanism: "Lava" of Ammonia/Water mixture,
lakes and vapor geysers of Nitrogen
(DEMO)
- Callisto (Jupiter moon) (picture)
- Size: exactly Mercury size
- Deep frozen,
not fully fractionated mixture of water ice and rock
- Surface older than 4 billion years - no geological
activity
- Lots of craters, but fuzzy edges as ice evaporates
somewhat
- Recent indication of liquid salt water ocean under
thick ice layer (see Europa)
- Ganymede (Jupiter moon) (picture)
- Size: slightly larger than Mercury
- Fractionated: Water ice crust, rock core
- Has magnetic field
- Some regions only ~1 billion years old
geologically active ! (plate tectonics ?)
- New findings about liquid water, probably
sandwiched between ice layers (see Europa)
- What heats Ganymede ?
Tidal forces from Jupiter (DEMO)
- Europa (Jupiter moon) (picture)
- Size: 65% Mercury (slightly bigger than earths
moon)
- Mainly rocky interior with ice surface, hot
metallic core
- Strong indications of liquid water ocean extending
down
to rocky interior underneath thin ice crust
- Recently formed surface features consistent
with thin ice crust and underlying liquid ocean
- Presence of salt detected
- Magnetic field changes consistent with currents
in liquid
salt water induced by Jupiters magnetic fields.
- Deep sea volcanic activity likely - life ?
- Io (Jupiter moon) (movie and picture)
- Size: 75% Mercury
- Highest level of volcanism in solar system
- Lava is hot silicate lava as on earth (>1000 oC)
- Large parts of the surface replaced within decades
(huge changes since Voyager flybys)
- Large deposits of sulfur snow - if snow melted by
eruption: huge gas plumes visible from space
- Sulfurdioxide atmosphere
- Titan (Saturn) (picture)
- Size: Slightly larger than Mercury
- A moon with a fuzzy, orange atmosphere that blocks
the view on the surface.
- Atmospheric pressure at surface: 1.6 bar (similar
to earth)
- Atmospheric composition: mainly Nitrogen (similar
to earth)
plus lots of compounds: CO, Hydrocarbons, Hydrogen
cyanide ...
Complex molecules form at high altitudes under impact
of UV light and block view
- Surface temperature: constant 90 K
(picture of surface layers)
- Surface images in infrared show inhomogeneous
surface
(picture)
- Ethane and Methane could form lakes, rivers, on the
surface (maybe an ethane wheather cycle, including
ethane rain).
- Visibility at surface might be good, surface
illumination
in a dark orange.
- The Cassini space craft is on the way to Saturn and
will drop a probe (Huygens) to land on Titan.
(see picture)
- Rings of the Giant planets (pictures
of rings pg 226/227 other
book)
- All Giant Planets have rings; only Saturns are easily
visible
- Rings are numerous pieces of ice, ranging in size from
dust grains to meter sized boulders
- Mostly water ice (white) but organic compounds on
surface can lead to dark rings
- Each particle orbits the planet like a little moon in a
well
confined plane (only 10-100 m thick)
- Rings are kept in place and structured by "shepards"
- Shepard moons within the ring systems sweep gaps
into the rings
- Gravity from all moons confine little pieces to
their
orbits (and sweep them out of certain unstable orbits)
keeping the rings in shape over time.
- Rings are probably very young (~50 Million years old)
- Rings form if a massive objects forms/enters the zone
within the tidal stability limit of a massive planet.
The object is disrupted and the pieces form a ring
- Triton is on the way and might be disrupted in ~100 Mio
years
- Jupiters rings: mainly smooth dust (dark), probably from inner
moons
- Saturns rings: Main rings A,B,C with Cassini Gap (4600
km)
between A and B. Plus thin outer F ring.
The A,B,C rings are very broad, very thin (~20 m)
quite bright and easily visible from earth
Closeup: really >1000 individual rings (picture)
- Uranus rings (9 main): narrow, many meter sized boulders, hardly
dust
and very dark (among darkest objects in solar system)
- Neptune rings (4): very inhomogeneous (look like thin arcs)
(picture)