reading: Chapter 8

Lecture 29. Jupiter and the Galilean Moons; Tides and Friction.

The Galilean Moons

First observed by Galileo in 1610 with a homemade telescope.First saw 3 “stars” near Jupiter.Next day, saw that they moved the “wrong” way.A few days later, a 4th “star” appeared.After a week, saw they moved with Jupiter, and changed position.Provided support for the Copernican model of the solar system.Not everything revolved around the Earth.

The largest of Jupiter’s16 moons.

Surface Cross-section

Diameter (km) Average density

Orbit (Earth days)

Io 3643 highest (rocky)

1.77 (x)

Europa 3122 3.55 (2x)

Ganymede 5262 7.16 (4x)

Callisto 4821 lowest (icy) 16.69 (9.5x)

PropertiesEarth: 12,700 kmMars: 6,800 kmMoon: 3476 km

Orbits

Density decreases with distance from Jupiter.All orbit in a plane around Jupiter.

Io orbits every 1.7 Earth days.IEG in orbital resonance (1:2:4)

Nearly all the Moons are in synchronous rotation -the same face always turned towards Jupiter

In this location, have more ices than rockyelements, so bodies tend to be more icy

Average density of Jovian Moons lower than Earth’s density

Jupiter’s Moons: largely water-iceUranus’ Moons: larger amounts of methane and ammonia ice

What does this imply about the formation of the Galilean Moons?

a simulation

Jupiter’s Other 12 Moons

-are smaller-have irregular shapes-orbits are highly elliptical-orbits not in the plane of the Galilean Moons-some are rocky and some are icy

What does this imply about the formation of Jupiter’s small Moons?

Io

Rocky moon - composed of molten silicate rockHas a core of Fe

Big surprise to Voyager scientists - geologically active.Few if any impact craters.

Hundreds of calderas - huge volcanic cratersVoyager showed active plumes erupting 300 km highPlumes are constant eruptions - like geysers.Gravity is 1/6g.Erupting material: some form of sulfur (SO2?)Turns to sulfur snowflakes when it hits the cold of space.Eruptions change rapidly.4 months between V1 and V2: some volcanoes started, others

stopped, deposits surrounding the vents changedMost of the plumes were stable

Volcanoes on Io

Io’s hot spots: 125 trillion watts!Volcanic activity was predicted in a research paper published one

week before V1 flyby of Jupiter.

Little or no water on Io. Why is that?

Lakes of molten sulfurExtensive flows of sulfur (?) -> colorsS2 gas erupted from vents, turns into S3 & S4 (red) then S8 (yellow)Volcanoes have T’s of 1500˚C - basalt lavas

Europa

Similar in bulk composition to Io, but has a thin layer of ice.Layered internal structure.Ice layer, few km thick?Liquid water layer, 50 km thick?

Only 3 craters > 5 km across.Age of the surface unknown.

Little topography: few features > few hundred meters highImages resemble sea ice on Earth.

Has an extremely thin atmosphere of O2 (10-11 bars)

Bands

Surface fractured creating dark linear, curved, wedge-shaped bandsBreaks ice into plates of 30 km across.Areas between plates filled with icy slush and rock (?)

Ice Rafts/Chaos Regions

Plates ~13 km across.Broken apart, floated into new position, refroze.Ice must have been watery or soft.Looks like pack ice in the Earth’s polar regions.

False-color image.Reds & browns: contaminants in the ice

Ridges

Cross-cuttingFaultsForm by compressionAre 8km wideForces change direction

Generations of Ridges

Tides

Gravity of the Moon attracts matter onthe Earth

Matter closest to the Moon feels moregravitational interaction

Causes distortion.Force not enough to affect rock.But it does affect water.

Two tidal bulges on the EarthA. water pulled toward the MoonB. Earth pulled toward the Moon

(away from the water)

Tides, cont.

Tides move because Earth rotates.

animation.

As the tidal bulge rotates, the Moon’sgravity pulls at the bulge.

This causes drag/tidal friction.This slows down the Earth’s rotation

by 1 sec/50,000 years.

Earth and Moon losing rotationalenergy, are slowly moving apart.image copyright: Nick Strobel’s

Astronomy Noteswww.astronomynotes.com

Tides on Moons

The Earth also raises tides on the Moon.Drag/friction slowed down the Moon’s rotation until the

tidal bulge never moved.Earth is now locked into synchronous orbit.

Planets have higher gravitational fields than Moons, so Moons go into synchronous orbit.

Jupiter is so big, it Moons were likely locked into synchronous orbit a few million years after formation.

Tidal friction generates drag and heat.

Tides on Io

Changing tidal bulge on Io causes the Moon to bestretched and squeezed.

Io in a tug-of-war with Jupiter, Europa, and Ganymede:

Tidal bulges in the solid crust of Io 100 meters (Earth: ~1 m)!

Flexing causes heating.

Tides on Europa

Tidal heating also of Europa.Tidal heating melting ice and making a liquid water ocean.

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Water circulating through heated mantle material - producinghydrothermal vents.

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Lecture 30. Jupiter and the Galilean Moons; Magnetic Moments.

reading: Chapter 8

Ganymede