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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.