Transcript
Page 1: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Satellites of Jupiter

Lecture 23

Page 2: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Galilean Satellites Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites as seen from Earth. All four orbits lie in nearly

the same plane as Jupiter’s equator.

Page 3: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

•Heat from the protosun made it impossible for icy grains to survive within the innermost 2.5 to 4 AU of the solar nebula. • In the same way, Jupiter’s

heat evaporated any icy grains that were too close to the center of the “Jovian nebula.” Hence, the two inner Galilean satellites were formed primarily from rock, while the outer two incorporated both rock and ice.

Formation of Galilean Satellites

Page 4: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Io : most active volcanic site in the Solar SystemThe unique coloration of Io is a result of its tremendous volcanic activity.

The brilliant orange is due to sulfur ejected from the volcanoes. The white is probably sulfur snow.

Page 5: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Io’s Active Volcanoes

Page 6: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Io seen from Galileo Spacecraft

Lave Flow

IR view of volcanoes

Page 7: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Magnetic field interaction with Io When charged particles in Jupiter's magnetosphere collide with Io’s volcanic plumes

and with Io's surface, ions are knocked out of the plumes and off the surface. The result is a huge doughnut-shaped ring of electrons and ions, called the Io torus, that encircles Jupiter.

Page 8: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Tidal Friction Synchronous Rotation

Even a larger effect on the Moon Adjusting rotational+orbital motions until

“bulges” on the Moon always face to the Earth Synchronous Rotation = “Tidal Locking”

Tidal locking takes a short time (a few Myrs!) All close-in objects to a larger objects are

tidally locked-in!

Page 9: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Tidal Heating

We know that Mercury and Moon had lost their internal energy… 1979 Voyager 1 image of Io active volcano!! But Io is smaller than Mercury! Io is the most volcanically active place in the solar system. If Io was completely “tidally locked”, there shouldn’t be on-going heating..

Page 10: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Io : Continuing tidal heating…

Due to its elliptical orbit, bulges are “misaligned” w.r.t. Jupiter!continuing tidal friction increased internal heat!This internal heat is ~200 times more than Earth’s radioactive decay heat energy!But, tidal locking forces the orbit to be circular. ? Why Io’s orbit is elliptical still?

Page 11: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Move in Harmony : Orbits of Galilean Satellites

Page 12: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Orbital resonance

Three inner most Galilean moons orbit Jupiter in a resonant way…Periodic alignments exert force on each other smallest, shortest orbit got influenced the most Io’s orbit is “distorted” to be elliptical!Initially, Io’s rotation was faster and it was located closer to Jupiterbeing tidally lockedmoving outward“meet” Europa and formed 1:2 resonance.Io+Europa being tidally locked together and moving outwardThey “meet” Ganymede and formed a resonance 1:2:4Three of them are being moving outward to meet Callisto now…

Page 13: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Europa

Diameter – 3138 km (slightly smaller than Earth’s Moon)

Mass – less than Earth’s moon ( 1/125th of Earth’s mass, 65% of lunar mass)

Distance from Jupiter ~ 410,000 miles ( more than Earth - Moon), period=3.55 days

Has a very weak magnetic fieldHas a very tenuous atmosphere – about 10-11

bar of mostly oxygen gas.Surface is exceedingly smooth with highest

elevations of a few hundred meters high.The smooth surface has few craters but lots

of cracks

Existence of water was already known from the ground-based spectrum of Europa

Page 14: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Surface feature of Europa

Chaotic terrain : “…a surface that looked as if it had been clawed by a tiger with talons several

kilometers wide,…” Closer views resolved each line into a groove flanked by ridges. The larger channels travel thousands of kilometers along great circles without being

diverted by the terrain. Whatever mechanism formed them must explain this tendency.

Repeated tidal cracking and compression of ice is too chaotic a process to explain

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Enigma…

Conventional explantion

If true, we should be able to findsome single ridges. But, all Europanridges are double ridges!

Page 16: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Fissures, cracks, domes, and pits…

Page 17: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Broken Ice and Refrozen Water

chaotic terrain (top left); an enigmatic dark spot nicknamed “The puddle” (bottom left); cycloidal ridges (right); and a shallow impact crater (bottom right).

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Moving Ice on Europa and Earth Some time after a series of ridges formed in this region of Europa’s surface, the icy

crust broke into “rafts” that were moved around by an underlying liquid or plastic layer.

Page 19: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Europa Craters 140 km wide crater formed from a mountain size asteroid or comet… similar to a gunshot glass structure… Thickness of the ice crust is estimated to be ~20km

Page 20: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

How do we measure the thickness of the ice crust? Compare morphology of various impact craters.

Top: impact craters on Ganymede and Callisto Bottom: impact craters on Europa

Page 21: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Europa Galileo spacecraft measured gravitational field of Europa dense core + low density (≈1 g/cm3; some sorts of water) material near the surface

central metallic core, thick rocky interior, 80-170km thick water layer, very cold (-150C) surface ice crust.

Galileo orbiter image = very few impact craters young surface (≤ 100 Myr)…

Severe lacking of impact craters (only a few) surface younger than 100 Myr resurfacing by occasional breakthrough of subsurface water

Page 22: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Subsurface Ocean Life in Europa

The global ocean on Europa contains about twice the liquid water of all the Earth’s oceans combined. There may be plenty of oxygen available in that ocean to support life, a hundred times more oxygen than previously estimated.

Page 23: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Ganymede

the largest moon in the solar system

surface of hard iceold + young surfacesgrooves tectonic stressesunderground ocean weak

induced magnetic field (+ its own) & surface salt.

lesser tidal heating. But with its larger size, enough to maintain an ocean

Very thick ice crust (>150km) life less likely or harder to detect!

Page 24: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Ganymede

white craters and rims = impact exposes mantle icethin oxygen atmosphere,

possible aurora at its poles

ghost craters = smoothed by ice flow

very diversified surface with dark regions, valleys, mountains, evidence of past tectonic activity and lots of vertical relief

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Callisto

pockmarked surface as old as late heavy bombardment

dark powder at the low-lying areas dusts after sublimated ice? Gravity a ball of mixed rock and ice + hundred km of water ice… Undifferentiated interior interior was never warm enough! Induced magnetic field subsurface salty ocean!!

Page 26: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Interior of Galilean Satellites probable internal structures of the four Galilean satellites of Jupiter, based on

information from the Galileo mission.

Page 27: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

Galilean Moons

Too hot Maybe less likely Too cold, no?

Io Europa Ganymede Callisto

recent < 60 Myr 2-3 Gyr? 4+ Gyr

Page 28: Satellites of Jupiter Lecture 23. Galilean Satellites Io, Europa, Ganymede, Callisto Io, Europa, Ganymede, Callisto Orbits of the four Galilean satellites

In summary…

Important ConceptsFormation of Galilean satellites

(scaled-down version of Solar System formation)

Io’s prolonged volcanismSubsurface oceans in Europa and

GanymedeGeological activities on these

moons

Important TermsOrbital resonanceIo torusTidal heating

Chapter/sections covered in this lecture : 13.1 through 13.7


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