Jupiter & Saturn The Moons Shortened Version Feb 15, 2011

Moons of the Planets  Earth 1  Mars 2  Jupiter63  Saturn47  Uranus27  Neptune13  Pluto 3 Total 156 (as of Nov. 8, 2005) Total 156 (as of Nov. 8, 2005) Galileo (1610) found the first four moons of Jupiter.

Jupiter’s Galilean satellites are easily seen 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 same size and density as our Moon  They are composed principally of rocky material  The two outermost Galilean satellites, Ganymede and Callisto, are roughly the size of Mercury  Lower in density than either the Moon or Mercury, they are made of roughly 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

Io How can a small body like Io remain hot enough inside to produce such vigorous volcanic activity ?????

Tidal Heating  The energy to heat Io’s interior and produce the satellite’s volcanic activity comes from tidal forces that flex the satellite  This tidal flexing is aided by the 1:2:4 ratio of orbital periods among the inner three Galilean satellites

Why Io is hot inside Io is pulled by the gravity of Europa and Ganymede, plus Jupiter. A resonance of 2:1 with Europa and 4:1 with Ganymede keeps Io’s orbit slightly elliptical. (Remember what a resonance is ?) Jupiter keeps trying to make the orbit more circular. The gravity pull causes Io to bend and flex. This flexing produces heat that keeps the interior molten. What’s this for?

Io’s Volcanoes  At least 16 volcanoes are known, and 4-8 are erupting at any one time  Io’s volcanoes erupt about 500 cubic km of lava each year – more than 100 times as much as all of Earth’s volcanoes  Eruptions on Io can shoot gas and particles up to 300 km (190 miles) above the surface

Io’s Volcanoes  Some of the eruptions are powered by sulfur dioxide (SO 2 ) gas, which is also found in Earth’s volcanoes.  Much of Io’s surface is covered with frozen sulfur (yellow and black) and SO 2 ice (white).  Io’s volcanic eruptions produce a thin and variable atmosphere, mostly of SO 2. Auroras 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

Europa

Europa Europa has no impact craters. It’s icy surface shows an intricate network of crossing cracks, similar to cracks in the Arctic ice pack on Earth. There is very little vertical relief (no mountains or deep valleys). Europa’s surface is very young.

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 crust

Amazing structures in the icy crust of Europa

Broken and tilted icebergs floating in a frozen sea

Broken and tilted blocks of ice

Remains of impact craters ? The flowing ice has filled them in.

Europa is heated by gravitational effects of Ganymede and Jupiter (like Io), and therefore it has an interior layer (“mantle”) of liquid water.

Could anything be living in the global ocean of Europa ? Microbes ? More advanced creatures ? NASA is considering a mission to Europa, to land and drill through the ice crust to get access to the liquid ocean below. ?

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-sized moons 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 Solar System Orbital period around Saturn is 16 days Thick atmosphere made mainly of N 2 (nitrogen) with a small amount of CH 4 (methane), which is a hydrocarbon. Many other hydrocarbons also present.

Titan  Surface pressure is about 1.5 bars  Surface temperature -180 C (= -290 F)  Titan would be colder, but it has a greenhouse effect that warms the atmosphere. (Which gas is a greenhouse gas on Titan?)  The atmosphere is nearly opaque with organic smog, produced by sunlight acting on methane and nitrogen.  We can see the surface indistinctly at certain wavelengths where the atmosphere is partly transparent.

Titan has a thick, opaque atmosphere rich in 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 spacecraft as it orbits Saturn. The Huygens probe was detached from Cassini and entered Titan’s atmosphere in January It descended through the atmosphere, making scientific measurements, and landed on Titan’s surface, where it continued to make measurements for a few hours.

Huygens Probe Jettisoned, December 25, 2004

Huygens’ Descent into Titan’s Atmosphere January 14, 2005

Titan’s Atmosphere and Surface

Organic Chemistry on Titan N 2 -atmosphere with a few % CH 4 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 Titan  Hydrocarbon dust forms in atmosphere  Dust settles on land (H 2 O ice) (H 2 O ice)  Methane (CH 4 ) rains on Titan, washing hydrocarbon dust into streams and lakes Images from the descent Probe cameras

Titan’s Surface  Liquid methane may emerge from springs, forming channels as it flows downhill

Titan’s Surface Islands in a stream channel formed by flowing liquid methane

 Titan landscape from Huygens lander, January 14, 2005  Rounded boulders in foreground are about cm across.  The boulders are probably frozen H 2 O.

Titan Summary  Titan has a thick atmosphere in which there is the active formation of complex organic chemicals.  These may be the chemicals that formed on the Earth preceding the origin of life on our planet.  We study Titan to learn about the chemistry of our own planet, and about other worlds where the chemistry of life exists.

So many moons, so little time …