Transcript Saturn, the ringed planet, and its strange moons

Size comparison of the Outer Planets
Earth
Neptune
Uranus
Early telescopic observations of Saturn
a. Galileo, 1610;
b. Huygens 1655;
c. Cassini 1676
Spacecraft that have visited Saturn
• Pioneer 11 flew within 21,000 km of Saturn on 1
September 1979, discovered two new moons and an
additional ring, charted Saturn's magnetosphere and
magnetic field and found its planet-size moon Titan, to
be too cold for life.
• The Voyager 1 and 2 Saturn encounters occurred nine
months apart, in November 1980 and August 1981.
Discovers larger of internal to external heat: 2-to-1
compared to 1-to-1 for Jupiter.
• Cassini orbital insertion on July 1, 2004. Took first
image of a moon (Phoebe) on June 11, 2004. Still
working in April 2006:
http://photojournal.jpl.nasa.gov/mission/Cassini
• Cassini dropped the Huygens probe into atmosphere of
Titan on January 14, 2005.
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Cassini
spacecraft;
launched on Oct.
15, 1997 from
KSC
7 Year cruise on Venus-Venus-Earth-Jupiter
Gravity Assist Trajectory
The Cassini Spacecraft
Interior Structure of Saturn
Like on Jupiter, there are latitudinal bands of clouds and storms
Ribbon clouds in atmosphere – high-speed turbulence
Wind speeds at top of Saturn’s Atmosphere
Opposite
direction
1700 km/hr
Multiple Rings!
Cassini Division
D
C
B
Encke Gap
A
F
E Ring extends to 7.5 Saturn radii from cloud top
Structure: Non-symmetric on each side of Saturn
Braided F-Ring of Saturn due to co-orbiting “shepherd” moons
Two shepherd satellites confine Saturn’s narrow F ring.
The outer shepherd gravitationally deflects ring particles inward, and the inner shepherd
deflects ring particles outward.
Prometheus
<R> = 47 km, Density = 0.42
Pandora
<R> = 41 km, Density = 0.54
Ring Spokes – Dust above the ring plane
The Smaller Moons of Saturn
Janus
Telesto
Prometheus
Helene
Atlas
Calypso
Pandora
Epimetheus
Janus
<R> = 90 km, Density = 0.61
Epimetheus
<R> = 58 km, Density = 0.64
Mimas, 392 km in diameter
Herschel Crater is 130 km wide and 10 km deep!
Enceladus – 500 km in diameter
Diverse surface, with some tectonics
Enceladus
Tethys – 1,060 km in diameter. Heavily cratered, with some lineaments
Dione – 1,120 km in diameter. Bright surface swirls, many craters
Rhea – 1,530 km in diameter. Very heavily cratered
Various spacecraft views of Titan – 5,150 km in diameter
Cassini visible light image
Pioneer 11
Voyager 1
Cassini
nearIR
image
What do we know about Titan?
• It is the biggest of Saturn’s moons.
• Titan’s diameter of 5,150 km makes it larger than the
planet Mercury with a diameter of 4,880 km and Pluto
(2,350 km).
• Only Jupiter's moon Ganymede is larger.
• Three-and-a-quarter Earth Moons could fit inside
Titan.
• Titan is the only moon known to have a large
atmosphere – maybe thicker than Earth’s (>1,000 mb)!
• Its atmosphere is mostly nitrogen, just like the
atmosphere surrounding Earth, but thicker.
• Its atmosphere contains methane and tiny amounts of
oxygen.
Comparison of Titan’s atmosphere with Earth’s
Important gases in Titan’s atmosphere
1. Ethane-methane lakes
3. Sedimentation of aerosols
2. Moist convection in methane clouds
4. Elevated terrain washed by rain
3.
2.
1.
4.
January 14, 2005 – Huygens Probe sent to Titan’s surface
Huygens scientific instruments
• Aerosol Collector and Pyrolyzer: collects Titan's aerosols for
chemical composition analysis;
• Descent Imager/Spectral Radiometer: makes spectral
measurements and takes pictures of Titan's surface and
atmospheric hazes;
• Doppler Wind Experiment: uses radio signals to deduce wind
speeds on Titan;
• Gas Chromatograph/Mass Spectrometer: identifies and
quantifies various atmospheric constituents on Titan;
• Surface Science Package: determines the physical properties
of Titan's surface.
Radar Image of Titan’s surface – valley systems
Few impact craters seen on Titan – implies young surface
Surface image from Huygens probe
Horizon at 66 m
30 cm diameter
15 cm diameter
Range 240 cm
Range 85 cm
Iapetus – 1,460 km in diameter. Striking albedo differences
Cassini Views of Iapetus
Iapetus is 1,460 km diameter
Orbits 59.1 Saturn radii from planet
100 km
What’s Interesting about Phoebe?
• Phoebe is roughly spherical and is ~220 km in diameter.
• Phoebe rotates on its axis every 9 hours and orbits Saturn in ~18
months.
• Its irregular, elliptical orbit is inclined ~30 degrees toward
Saturn’s equator.
• Phoebe’s orbit is retrograde.
• Phoebe’s average distance from Saturn is 13 million km, which is
~4 times farther away from Saturn than its nearest neighbor, the
moon Iapetus.
• Phoebe and Iapetus are the only major moons in the Saturn region
that do not orbit close to the plane of Saturn’s equator.
• Unlike most major moons orbiting Saturn, Phoebe is very dark
and reflects only 6 percent of the sunlight it receives.
Saturn’s moon Phoebe
Identification of surface materials on Phoebe
Saturn Summary