Survey of Astronomy Astro1010-lee.com [email protected] Chapter 12 Saturn.
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Survey of Astronomy A s t r o 1 0 1 0 - l e e . c o m [email protected] om Chapter 12 Chapter 12 Saturn
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Transcript of Survey of Astronomy Astro1010-lee.com [email protected] Chapter 12 Saturn.
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Chapter 12The Spectacular Saturn System
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Chapter 12Mass: 5.7 × 1026 kg
Radius: 60,000 km
Density: 700 kg/m3 – less than water!
Rotation: rapid and differential, enough to flatten Saturn considerably
Rings: very prominent; wide but extremely thin
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Chapter 12Saturn’s atmosphere is
similar to Jupiter’s, except the pressure is lower
Three cloud layers
Cloud layers and the haze layer are deeper than Jupiter’s and more dense
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Chapter 12
Like Jupiter Saturn has stripes and differential rotation. They are much more subdued and are rarely seen through Saturn’s haze and cloud cover. Jupiter-style “spots” are rare on Saturn. They don’t form as often and quickly dissipate if they do
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Chapter 12Saturn also has a
strong magnetic field, but only about 5% as strong as Jupiter’s. It has Van Allen Belts where charged particles from the Solar Wind are trapped and they produce aurorae.
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Chapter 12Historically , only one ring was seen. As our
instruments got better we were able to distinguish more detail. The rings are labeled by letter in the order of their discovery.
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Chapter 12
Ring particles range in size from fractions of a millimeter to tens of meters
They are made of dust and rock covered with water ice
Why rings? They are too close to planet for moon to form – tidal forces would tear it apart
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Chapter 12Closest distance that a moon could survive is
called the Roche limit; planetary ring systems are all inside this limit
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Chapter 12The Voyager probes showed Saturn’s rings
to be much more complex than originally thought
The Earth is shown on the same scale as the rings
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Chapter 12The Cassini division
turns out not to be completely empty. The gap seems to be caused by an orbital resonance with other ring particles and Saturn’s innermost moon
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Chapter 12
Voyager also found radial “spokes” that formed and then dissipated; this probably happens frequently
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Chapter 12It was expected that sharp edges and
divisions in the Rings would be caused by ‘Shepherd Moons’. It was not so. The other edges and divisions in the rings now seem to be the result of resonance.
However, a “Shepherd” moon does define the outer edge of the [A] ring through gravitational interactions.
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Chapter 12
Strangest ring is the F ring . It appears to have braids and kinks.
F ring’s oddities are probably caused by’ two ‘Shepherd Moons’, one of which can be seen here
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Chapter 12Details of ring formation are unknown
It is thought that rings are too active to have lasted since the birth of the solar system
Either they must be continually replenished, or they are the result of a catastrophic events
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Chapter 12Saturn’s many moons appear to be made of
water ice or carbon based rocks covered with ice
Besides the small moons, Saturn has:
Six medium-sized moons (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus)
One large moon (Titan) which is almost as large as Ganymede
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Chapter 12Saturn’s many moons appear to be made of water
ice or carbon based rocks covered with ice. There are six medium-sized moons and one large moon (Titan) which is almost as large as Ganymede
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Chapter 12Titan has an atmosphere thicker and denser than
Earth’s. It is made mostly of nitrogen and argon but it also has some very interesting chemistry in its upper atmosphere.
The surface can NOT be seen through the haze. This image was taken by Voyager I from only 4000 km away
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Chapter 12After Voyager there was much desire to
learn more about Titan and the Saturn system. The Cassini Orbiter and the Huygens Probe were sent to make that Study.
This artist’s impression is of Cassini as the Huygens Probe was released.
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Chapter 12The Huygens Probe
analyzed the atmosphere of Titan as it descended. Many trace chemicals mostly derived from methane make the atmosphere chemically complex.
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Chapter 12During its descent
Huygens photographed the surface below. Here we see a shore line of a lake and a watershed feature that looks like a river system. The liquid is not water but liquid methane. The light colored patches seem to be methane frost or snow,
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Chapter 12On 9/16/05
Huygens landed on a slushy area dotted with boulders composed of water ice, under orange clouds composed of complex hydrocarbons
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Chapter 12Mimas, Enceladus, Tethys, Dione, and Rhea all orbit
between 3 and 9 planetary radii from Saturn, and all are tidally locked – this means they have “leading” and “trailing” surfaces. Iapetus orbits 59 radii away, and is also tidally locked
The medium sized moons are shown on scale with the Earth’s Moon
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Chapter 12
Rhea, the largest, has a highly reflective, heavily cratered surface. The wispy features are on the trailing side but not the leading; their origin is not yet fully understood.
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Chapter 12Dione and Tethys are similar, having icy, heavily
cratered surfaces
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Chapter 12Mimas is the closest moon to
Saturn, and has a crater covering one-third of its surface, the result of an impact that must have almost destroyed the moon
Iapetus is two-faced: its leading side is very dark (reflects 3% of incoming light), while its trailing side is bright (reflects 50% of incoming light).
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Chapter 12This moon possesses a region of terrain
near its south pole that is dramatically devoid of impact sites. Scientists suspected it is geologically active. The discovery in 2009 of material jetting from the pole and creating a great plume of icy particles confirmed these suspicions. The Cassini continues to study it because it seems to have liquid water inside.
Enceladus orbits close to Mimas, but is very shiny, indicating a surface covered with ice crystals
