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’s 16 moons.

SurfaceCross- section Diameter (km)Average density Orbit (Earth days) Io3643highest (rocky) 1.77 (x) Europa (2x) Ganymede (4x) Callisto4821lowest (icy)16.69 (9.5x) Properties Earth: 12,700 km Mars: 6,800 km Moon: 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 rocky elements, so bodies tend to be more icy Average density of Jovian Moons lower than Earth’s density Jupiter’s Moons: largely water-ice Uranus’ 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 rock Has a core of Fe Big surprise to Voyager scientists - geologically active. Few if any impact craters. Hundreds of calderas - huge volcanic craters Voyager showed active plumes erupting 300 km high Plumes are constant eruptions - like geysers. Gravity is 1/6g. Erupting material: some form of sulfur (SO 2 ?) 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 changed Most 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 sulfur Extensive flows of sulfur (?) -> colors S 2 gas erupted from vents, turns into S 3 & S 4 (red) then S 8 (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 high Images resemble sea ice on Earth. Has an extremely thin atmosphere of O 2 ( bars)

Bands Surface fractured creating dark linear, curved, wedge-shaped bands Breaks 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-cutting Faults Form by compression Are 8km wide Forces change direction Generations of Ridges

Tides Gravity of the Moon attracts matter on the Earth Matter closest to the Moon feels more gravitational interaction Causes distortion. Force not enough to affect rock. But it does affect water. Two tidal bulges on the Earth A.water pulled toward the Moon B.Earth pulled toward the Moon (away from the water)

Tides, cont. Tides move because Earth rotates. animation. As the tidal bulge rotates, the Moon’s gravity 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 rotational energy, are slowly moving apart. image copyright: Nick Strobel’s Astronomy Notes

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 be stretched 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. Water circulating through heated mantle material - producing hydrothermal vents.

Lecture 30. Jupiter and the Galilean Moons; Magnetic Moments. reading: Chapter 8

Ganymede