Jupiter & SaturnJupiter & Saturn

The MoonsThe MoonsShortened Version Feb 15, 2011

Moons of the PlanetsMoons of the Planets

EarthEarth 1 1 MarsMars 2 2 JupiterJupiter 6363 SaturnSaturn 4747 UranusUranus 2727 NeptuneNeptune 1313 PlutoPluto 3 3

Total Total 156 (as of Nov. 8, 156 (as of Nov. 8, 2005)2005)

Galileo (1610) found the firstfour moons of Jupiter.

Jupiter’s Galilean satellites are easily Jupiter’s Galilean satellites are easily seen with Earth-based telescopesseen with Earth-based telescopes

The four Galilean satellites orbit Jupiter in the plane of its equator

All are in synchronous rotation

The orbital periods of the three innermost Galilean satellites, Io, Europa, and Ganymede, are in the ratio 1:2:4

Data from spacecraft reveal the unique properties

of the Galilean satellites

The two innermost Galilean satellites, Io and Europa, have roughly The two innermost Galilean satellites, Io and Europa, have roughly the same size and density as our Moonthe same size and density as our Moon

They are composed principally of rocky materialThey are composed principally of rocky material The two outermost Galilean satellites, Ganymede and Callisto, are The two outermost Galilean satellites, Ganymede and Callisto, are

roughly the size of Mercuryroughly the size of Mercury Lower in density than either the Moon or Mercury, they are made of Lower in density than either the Moon or Mercury, they are made of

roughly equal parts ice and rockroughly equal parts ice and rock

The Galilean satellites formed like a solar system in miniature

The Galilean satellites probably formed in a similar

fashion to our solar system but on a smaller scale

Io is covered with colorful sulfur compounds ejected from active volcanoes

IoIoHow can a smallbody like Ioremain hotenough insideto producesuch vigorousvolcanic activity ?????

Tidal HeatingTidal Heating

The energy to heat Io’s The energy to heat Io’s interior and produce the interior and produce the satellite’s volcanic activity satellite’s volcanic activity comes from tidal forces that comes from tidal forces that flex the satelliteflex the satellite

This tidal flexing is aided by This tidal flexing is aided by the 1:2:4 ratio of orbital the 1:2:4 ratio of orbital periods among the inner periods among the inner three Galilean satellites three Galilean satellites

Why Io is hot insideWhy Io is hot insideIo is pulled by the gravity of Europa and Ganymede, plusJupiter.

A resonance of 2:1 with Europa and 4:1 with Ganymedekeeps Io’s orbit slightly elliptical. (Remember whata resonance is ?)

Jupiter keeps trying to make the orbit more circular.

The gravity pull causes Io to bend and flex. This flexingproduces heat that keeps the interior molten.

What’s this for?

Io’s VolcanoesIo’s Volcanoes

At least 16 volcanoes are known, and 4-8 are At least 16 volcanoes are known, and 4-8 are erupting at any one timeerupting at any one time

Io’s volcanoes erupt about 500 cubic km of Io’s volcanoes erupt about 500 cubic km of lava each year – more than 100 times as much lava each year – more than 100 times as much as all of Earth’s volcanoesas all of Earth’s volcanoes

Eruptions on Io can shoot gas and particles up Eruptions on Io can shoot gas and particles up to 300 km (190 miles) above the surfaceto 300 km (190 miles) above the surface

Io’s VolcanoesIo’s Volcanoes

Some of the eruptions are powered by sulfur Some of the eruptions are powered by sulfur dioxide (SOdioxide (SO22) gas, which is also found in ) gas, which is also found in

Earth’s volcanoes.Earth’s volcanoes. Much of Io’s surface is covered with frozen Much of Io’s surface is covered with frozen

sulfur (yellow and black) and SOsulfur (yellow and black) and SO22 ice (white). ice (white).

Io’s volcanic eruptions produce a thin and Io’s volcanic eruptions produce a thin and variable atmosphere, mostly of SOvariable atmosphere, mostly of SO22. Auroras . Auroras

are seen in this atmosphere.are seen in this atmosphere.

Jupiter’s magnetic field makes electric currents flow through Io

The Io torus is a ring of electrically charged particles circling Jupiter at the distance of Io’s orbit

Interactions between this ring and Jupiter’s magnetic field produce strong radio emissions

Io may also have a magnetic field of its own

EuropaEuropa

EuropaEuropaEuropa has no impactcraters. It’s icy surfaceshows an intricate networkof crossing cracks, similarto cracks in the Arcticice pack on Earth.

There is very little verticalrelief (no mountains or deep valleys).

Europa’s surface is veryyoung.

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

As for Io, tidal heating is responsible for Europa’s internal heat

Minerals dissolved in this ocean may explain Europa’s induced magnetic field

Other indications are a worldwide network of long cracks and ice rafts that indicate a subsurface layer of liquid water or soft ice

Europa’s cracked and colored crustEuropa’s cracked and colored crust

Amazing structures in the Amazing structures in the icy crust of Europaicy crust of Europa

Broken and tilted icebergs floating in a frozen sea

Broken and tiltedblocks of ice

Remains ofimpactcraters ?

The flowingice has filled themin.

Europa is heated by gravitational effects of Europa is heated by gravitational effects of Ganymede and Jupiter (like Io), and therefore it has Ganymede and Jupiter (like Io), and therefore it has

an interior layer (“mantle”) of liquid water.an interior layer (“mantle”) of liquid water.

Could anything be living in the global ocean of Could anything be living in the global ocean of Europa ?Europa ?

Microbes ?More advanced creatures ?

NASA is considering a missionto Europa, to land and drillthrough the ice crust to getaccess to the liquid oceanbelow.

?

Liquid water may also lie beneath the cratered surfaces of Ganymede and Callisto

Ganymede Ganymede is highly

differentiated, and probably has a metallic core

It has a surprisingly strong magnetic field and a magnetosphere of its own

While there is at present little tidal heating of Ganymede, it may have been heated in this fashion in the past

An induced magnetic field suggests that it, too, has a layer of liquid water beneath the surface

Two types of terrain are found on the icy surface of Ganymede:

areas of dark, ancient, heavily cratered surface regions of heavily grooved, lighter-colored, younger terrain

Callisto has a heavily cratered crust of water ice 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 Magnetic field data seem to suggest that Callisto has a shallow subsurface ocean

Jupiter has dozens of small satellites that have different origins

As of early 2004, Jupiter has a total of 63 known satellites

In addition to the Galilean satellites, Jupiter has four small inner satellites that lie inside Io’s orbit

Like the Galilean satellites, these orbit in the plane of Jupiter’s equator

The remaining satellites are small and move in much larger orbits that are noticeably inclined to the plane of Jupiter’s equator

Many of these orbit in the direction opposite to Jupiter’s rotation

The icy surfaces of Saturn’s six moderate-sizedThe icy surfaces of Saturn’s six moderate-sizedmoons provide clues to their historiesmoons provide clues to their histories

As of early 2004, Saturn has a total of 31 known satellites

In addition to Titan, six moderate-sized moons circle Saturn in regular orbits: Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus

They are probably composed largely of ice, but their surface features and histories vary significantly

The other, smaller moons include shepherd satellites that control the shapes of Saturn’s rings and captured asteroids in large retrograde orbits

Enceladus (Moon of Saturn)Geysers of erupting liquid water announced in March 2006,

discovered by the Cassini spacecraft

This is probably the source of the “E” ring

Enceladus (Moon of Saturn)Geysers of erupting liquid water announced in March 2006,

discovered by the Cassini spacecraft

Enceladus (Moon of Saturn)Geysers of erupting liquid water announced in March 2006,

discovered by the Cassini spacecraft

Finding warm spots on the surface of Enceladus

Titan: Largest Moon in the Titan: Largest Moon in the Solar SystemSolar System

Orbital period aroundSaturn is 16 days

Thick atmosphere mademainly of N2 (nitrogen)with a small amount of CH4 (methane), which is a hydrocarbon.

Many otherhydrocarbons alsopresent.

TitanTitan Surface pressure is about 1.5 barsSurface pressure is about 1.5 bars Surface temperature -180 C (= -290 F)Surface temperature -180 C (= -290 F) Titan would be colder, but it has a Titan would be colder, but it has a greenhouse greenhouse

effecteffect that warms the atmosphere. (Which gas that warms the atmosphere. (Which gas is a is a greenhouse gasgreenhouse gas on Titan?) on Titan?)

The atmosphere is nearly opaque with organic The atmosphere is nearly opaque with organic smog, produced by sunlight acting on methane smog, produced by sunlight acting on methane and nitrogen.and nitrogen.

We can see the surface indistinctly at certain We can see the surface indistinctly at certain wavelengths where the atmosphere is partly wavelengths where the atmosphere is partly transparent.transparent.

Titan has a thick, opaque atmosphere richTitan has a thick, opaque atmosphere richin methane, nitrogen, and hydrocarbonsin methane, nitrogen, and hydrocarbons

The largest Saturnian satellite, Titan, is a terrestrial world with a dense nitrogen atmosphere

A variety of hydrocarbons are produced there by the interaction of sunlight with methane

These compounds form an aerosol layer in Titan’s atmosphere and possibly cover some of its surface with lakes of ethane

Titan is being explored by the Cassini spacecraftas it orbits Saturn.

The Huygens probe was detached from Cassiniand entered Titan’s atmosphere in January 2005.

It descended through the atmosphere, makingscientific measurements, and landed on Titan’ssurface, where it continued to make measurementsfor a few hours.

Huygens Probe Jettisoned, December 25, 2004Huygens Probe Jettisoned, December 25, 2004

Huygens’ Descent into Titan’s AtmosphereHuygens’ Descent into Titan’s Atmosphere

January 14, 2005

Titan’s Atmosphere and Surface

Organic Chemistry on TitanOrganic Chemistry on Titan

N2-atmosphere with a few % CH4

The chemistry in the atmosphere of Titan may resemble that which was at work on Earth 4 billion years ago, before the appearance of life.

Titan is a large prebiotic chemistry laboratory on a planetary scale.

But it’s very cold on Titan’s surface(-180 C), and there is no liquid water

Studying the chemistry on Titan today may be a way to sample Earth’s prebiotic chemistry 4 billion years ago.

Huygens finds flow channels on TitanHuygens finds flow channels on Titan

Hydrocarbon dust forms in Hydrocarbon dust forms in atmosphereatmosphere

Dust settles on land Dust settles on land

(H(H22O ice)O ice)

Methane (CHMethane (CH44) rains on ) rains on

Titan, washing hydrocarbon Titan, washing hydrocarbon dust into streams and lakesdust into streams and lakes

Images from the descent Probe cameras

Titan’s SurfaceTitan’s Surface

Liquid methane Liquid methane may emerge from may emerge from springs, forming springs, forming channels as it channels as it flows downhillflows downhill

Titan’s SurfaceTitan’s Surface

Islands in a stream Islands in a stream channel formed by channel formed by flowing liquid flowing liquid methanemethane

Titan landscape Titan landscape from Huygens from Huygens lander, January lander, January 14, 200514, 2005

Rounded Rounded boulders in boulders in foreground are foreground are about 4 - 15 cm about 4 - 15 cm across.across.

The boulders The boulders are probably are probably frozen Hfrozen H22O.O.

Titan SummaryTitan Summary

Titan has a thick atmosphere in which there is Titan has a thick atmosphere in which there is the active formation of complex organic the active formation of complex organic chemicals.chemicals.

These may be the chemicals that formed on the These may be the chemicals that formed on the Earth preceding the origin of life on our Earth preceding the origin of life on our planet.planet.

We study Titan to learn about the chemistry of We study Titan to learn about the chemistry of our own planet, and about other worlds where our own planet, and about other worlds where the chemistry of life exists.the chemistry of life exists.

So many moons, so little time …So many moons, so little time …