Ring systems - College of Charlestonneffj.people.cofc.edu/ASTR129/Notes/lec25.pdf · Major...
Transcript of Ring systems - College of Charlestonneffj.people.cofc.edu/ASTR129/Notes/lec25.pdf · Major...
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Lec 25: 5 December 2011 Chap. 13: Satellites of the Jovian Planets
TODAY - Small Worlds in the Outer Solar System • Io, Europa, Ganymede, Callisto, Titan, Triton • Intermediate Sized Satellites of Saturn & Uranus • Ring systems
Major Satellites in the Solar System • Moon (Earth), Io, Europa, Ganymede, Callisto
(Jupiter), Titan (Saturn), Triton (Neptune)
• all but Triton are tidally-locked (or almost so) • all large enough to have (or have had) internal
heat, differentiation, geological activity, etc. • recent/ongoing activity on at least 3 of them • high proportion of water ice (except Moon) • hemispheric asymmetries are common • at least 2 of them have atmospheres! • weak magnetic fields (slow rotators)
The “Galilean” Satellites of Jupiter Io has a bizarre, young surface!
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Volcanoes continuously erupt on Io Volcanoes continuously resurface Io
The Io “Plasma Torus”
• Ring of electrically charged particles circling Jupiter around Io’s orbit
• Interactions between this ring and Jupiter’s magnetic field produce strong radio emissions
• Io may have a magnetic field
Europa is covered with a smooth layer of ice that may cover a worldwide ocean
• While composed primarily of rock, Europa is covered with a smooth layer of water ice
• The surface has hardly any craters, indicating a geologically active history
• Tidal heating is responsible for Europa’s internal heat
• Minerals dissolved in this ocean may explain Europa’s induced magnetic field
• May harbor life!
Worldwide network of long cracks and ice rafts on Europa
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Ganymede
• Ganymede has a surprisingly strong magnetic field and magnetosphere
• While there is at present little tidal heating of Ganymede, it may have been heated in this fashion in the past
• Magnetic field suggests that it, too, has a layer of liquid water beneath the surface
• Two types of terrain on Ganymede: – dark, ancient, heavily cratered surface – heavily grooved, lighter-colored, younger terrain
• The surface shows little sign of geologic activity, because there was never any significant tidal heating of Callisto
• However, some unknown processes have erased the smallest craters and blanketed the surface with a dark, dusty substance (and light, young craters)
• Magnetic field data suggest that Callisto has a shallow subsurface ocean
Callisto has a heavily-cratered crust of water ice Interior Structure of the Galilean Satellites
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Titan Cassini/Huygens
To Learn More See...
saturn.jpl.nasa.gov
Triton • Triton has a young, icy
surface indicative of tectonic activity
• Triton orbits Neptune the WRONG WAY
• The energy for this activity may have been provided by tidal heating that occurred when Triton was captured by Neptune’s gravity into a retrograde orbit
• Triton has a tenuous nitrogen atmosphere
Triton and Pluto probably members a new class of “Trans-Neptunian Objects”
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Minor Satellites in the Outer Solar system • Saturn has 6 “medium” sized satellites on
regular equatorial orbits • Uranus and Neptune each have a few medium
sized satellites on regular orbits • many others are small, non-spherical, and on
irregular orbits (retrograde, chaotic, highly inclined, not tidally locked)
• these may be captured debris, not stuff that formed with the planets
• small satellites control structure of ring systems
Intermediate-sized satellites of Saturn
CONGRATULATIONS!!! First Semester: (ASTR129)
– How the Sky Appears from Earth – How and Why things move in the sky – Formation and Evolution of the Solar System – Properties of the Planets – Earth as a Planet
Second Semester: (ASTR130) – The Sun as a Star – Measuring basic properties of Stars – Birth, Life, and Death of Stars – Properties of Galaxies – Exotic things (like black holes) – Formation and Evolution of the Universe
Exam #3 Results: • median 72 • max 92 • Good Job!!
A >85 A-/B+ 75 - 85
B 65 - 75 C 55 - 65 D <55
Grade Scale:
Grade Weights: 75% exams
(lowest score can be replaced with final exam score)
25% “in-class” (quizzes, in-class exercises, attendance, participation)
Should you take the final? If one of your 3 exam scores was significantly lower than the others, taking the final exam is likely to improve your grade. Taking the final will NOT lower your grade.