The Jovian Planets Please pick up your transmitter and swipe your student ID.

The Jovian Planets (“Gas Giants”) Animation 1 Jupiter Saturn Uranus Neptune Animation 2 No well-defined surface!

Interior Structure

The Chemical Composition of Jupiter and Saturn

Jupiter Largest and most massive planet in the solar system: Contains almost ¾ of all planetary matter in the solar system. Explored in detail by several space probes: Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Galileo Most striking features visible from Earth: Multi-colored cloud beltsMulti-colored cloud belts Visual image Infrared false- color image

The Great Red Spot 8-year sequence of images of the Great Red Spot on Jupiter Has been visible for over 300 years Giant storm system similar to Hurricanes on Earth: Wind speeds of 430 km/h (= 270 miles/h) Changes appearance gradually over time

Jupiter’s Rotation Jupiter is the most rapidly rotating planet in the solar system: Rotation period slightly less than 10 hr.

Considering the rapid rotation of Jupiter, would you expect it to be perfectly round? :10 0 of Yes. 2.No, it should be oblate. 3.No, it should be prolate.

Jupiter’s Rotation Jupiter is the most rapidly rotating planet in the solar system: Rotation period slightly less than 10 hr. Centrifugal forces stretch Jupiter into a markedly oblate shape.

Jupiter’s Atmosphere Jupiter’s liquid hydrogen ocean has no surface: Gradual transition from gaseous to liquid phases. Only very thin atmosphere above cloud layers; transition to liquid hydrogen zone ~ 1000 km below clouds.

Jupiter’s Atmosphere (II) Three layers of clouds: 1. Ammonia (NH 3 ) crystals 2. Ammonia hydrosulfide (NH 4 SH) 3. Water crystals

Would you think that the atmosphere of Jupiter gets warmer towards lower altitudes because of the greenhouse effect? :10 0 of Yes: The atmosphere contains many greenhouse gases. 2.No, because of the dense cloud cover that reflects most of the sunlight. 3.No, because there’s no surface to absorb visible light and re-emit in infrared. 4.Both 2. and 3. are correct.

Jupiter’s Atmosphere (II) Three layers of clouds: 1. Ammonia (NH 3 ) crystals 2. Ammonia hydrosulfide (NH 4 SH) 3. Water crystals Heating mostly from latent, internal heat

The Cloud Belts of Jupiter Dark belts and bright zones. Zones higher and cooler than belts; high-pressure regions of rising gas.

The circulation patterns in the cloud belts are physically similar to which phenomenon on the sun? :10 0 of Sun spots. 2.Prominences. 3.Granulation (sub-photospheric convection). 4.Solar wind. 5.Coronal Mass Ejections.

The Cloud Belts on Jupiter (II) Just like on Earth, high-and low-pressure zones are bounded by high-pressure winds. Jupiter’s Cloud belt structure has remained unchanged since humans began mapping them.

Jupiter’s Magnetic Field Magnetic field at least 10 times stronger than Earth’s magnetic field. Magnetosphere over 100 times larger than Earth’s magnetosphere

Which factor might be the most important for Jupiter’s strong magnetic field? :10 0 of Its thick cloud belts. 2.A large liquid iron core. 3.A large solid iron core. 4.A large region of metallic hydrogen. 5.Its rapid rotation.

Aurorae on Jupiter Just like on Earth, Jupiter’s magnetosphere produces aurorae concentrated in rings around the magnetic poles. ~ 1000 times more powerful than aurorae on Earth.

At the location of Jupiter, is the flux of solar-wind particles (from the sun) stronger or weaker than at Earth? :10 0 of Stronger. 2.About the same as on Earth. 3.Weaker.

Aurorae on Jupiter Just like on Earth, Jupiter’s magnetosphere produces aurorae concentrated in rings around the magnetic poles. ~ 1000 times more powerful than aurorae on Earth. Particles producing the aurorae originate mostly from moon Io

The History of Jupiter Formed from cold gas in the outer solar nebula, where ices were able to condense. Rapid growth Soon able to trap gas directly through gravity Heavy materials sink to the center In the interior, hydrogen becomes metallic (very good electrical conductor) Rapid rotation → strong magnetic field Rapid rotation and large size → belt-zone cloud pattern Dust from meteorite impacts onto inner moons trapped to form ring

Jupiter’s Ring Not only Saturn, but all four gas giants have rings. Jupiter’s ring: dark and reddish; only discovered by Voyager 1 spacecraft. Galileo spacecraft image of Jupiter’s ring, illuminated from behind Composed of microscopic particles of rocky material Location: Inside Roche limit, where larger bodies (moons) would be destroyed by tidal forces.

Who discovered the largest moons of Jupiter? :10 0 of )Ptolemy 2)Galilei 3)Copernicus 4)Kepler 5)Newton

Jupiter’s Moons About 2 dozen moons known at this time, but more are being discovered … Largest and most prominent: 4 Galilean Moons (already discovered by Galilei in 1610): IoEuropa GanymedeCallisto

What happens to a soft rubber ball if you keep squishing and releasing it? :10 0 of )It will get gradually colder. 2)It will get gradually warmer. 3)None of the above.

Jupiter’s Influence on its Moons Presence of Jupiter has at least two effects on geology of its moons: 1. Tidal effects: possible source of heat for interior of Ganymede 2. Focusing of meteoroids, exposing nearby satellites to more impacts than those further out.

Io: Bursting Energy Most active of all Galilean moons; no impact craters visible at all. Over 100 active volcanoes! Interior is mostly rock. Activity powered by tidal interactions with Jupiter.

Interactions with Jupiter’s Magnetosphere Io’s volcanoes blow out sulfur-rich gases → tenuous atmosphere, but gases can not be retained by Io’s gravity → gases escape from Io and form an ion torus in Jupiter’s magnetosphere. → Aurorae on Jupiter are fueled by particles from Io

Europa: A Hidden Ocean composition: mostly rock and metal; icy surface. Close to Jupiter → should be hit by many meteoroid impacts; but few craters visible. → Active surface; impact craters rapidly erased.

The Surface of Europa Cracked surface and high albedo (reflectivity) provide further evidence for geological activity.

The Interior of Europa Europa is too small to retain its internal heat → Heating mostly from tidal interaction with Jupiter. Europa has a liquid water ocean ~ 15 km below the icy surface.

Would there, in principle, be life possible in the sub-surface ocean of Europa? :10 0 of Yes. 2.No, because there’s no light which is necessary for plant life. 3.No, because it’s too cold. 4.No, because it’s too warm. But it would have to be able to make use of heat provided by internal heat from the planet.

Ganymede: A Hidden Past Largest of the 4 Galilean moons. Rocky core Ice-rich mantle Crust of ice 1/3 of surface old, dark, cratered; rest: bright, young, grooved terrain Bright terrain probably formed through flooding when surface broke

Callisto: The Ancient Face Tidally locked to Jupiter, like all of Jupiter’s moons. composition: mixture of ice and rocks Dark surface, heavily pocked with craters. No metallic core: Callisto never differentiated to form core and mantle. → No magnetic field. Layer of liquid water, ~ 10 km thick, ~ 100 km below surface, probably heated by radioactive decay.

Saturn 2 nd largest planet; about 16 % smaller than Jupiter. 1/3 of Jupiter’s mass; density less than water: Saturn would float in water!! Atmospheric cloud structures similar to Jupiter’s, but less obvious. Rare, isolated storm systems. Rotates about as fast as JupiterRotates about as fast as Jupiter, but is twice as oblate → No large core of heavy elements.

Saturn 2 nd largest planet; about 16 % smaller than Jupiter. 1/3 of Jupiter’s mass; density less than water: Saturn would float in water!! Atmospheric cloud structures similar to Jupiter’s, but less obvious. Rare, isolated storm systems. Rotates about as fast as JupiterRotates about as fast as Jupiter, but is twice as oblate → No large core of heavy elements. Please press “1” to check your transmitter.

Saturn’s Atmosphere Three-layered cloud structure, just like on Jupiter Main difference to Jupiter: Fewer wind zones, but much stronger winds than on Jupiter: Winds up to ~ 500 m/s near the equator!

Saturn’s Magnetosphere Magnetic field ~ 20 times weaker than Jupiter’s Aurorae centered around poles

Saturn’s Rings Consisting of ice particles, from microscopic to several meters in size. Several sub- divisions: A-ring B-ring C-ring Cassini Division

Why did the material in Saturn’s rings not clump together to form another moon of Saturn? :10 0 of It was too cold to melt and clump together to form a moon. 2.It is mostly ice, which doesn’t stick together. 3.Tidal forces of the nearby planet kept pulling rocks apart. 4.It is too far away from Saturn, so it is not gravitationally bound to the planet.

Shepherd Moons Some moons on orbits close to the rings focus the ring material, keeping the rings confined.

What will happen to a small piece of rock orbiting Saturn, if its orbital period is exactly twice the orbital period of a moon that is orbiting further out? :10 0 of Nothing special. 2.It will be destroyed by tidal forces. 3.It will gradually be pushed inward and fall onto Saturn. 4.It will gradually be pulled outward, away from Saturn.

Divisions and Resonances Moons do not only serve as “Shepherds”. Where the orbital period of a moon is a small-number fractional multiple (e.g., 2:3) of the orbital period of material in the disk (“resonance”), the material is cleared out → Divisions

The Moons of Saturn Largest moon: Titan: The only moon in the solar system with an atmosphere: Mostly Nitrogen, but also traces of organic compounds like Methane and Ethane

Uranus Hubble-Space-Telescope image (rings artificially enhanced) 4 times larger than Earth (in radius) 14.5 times the mass of Earth Faint rings, indirectly detected through occultations Discovered in 1781 Rotation axis inclined by 97 0 against the orbital axis: Uranus is “rolling” on its orbitinclined by 97 0 Uranus is “rolling” on its orbit

The Rings of Uranus Rings of Uranus and Neptune are similar to Jupiter’s rings. Confined by shepherd moons; consist of dark material. Rings of Uranus were discovered through occultations of a background star Apparent motion of star behind Uranus and rings

The Atmosphere of Uranus Like other gas giants: No surface. Gradual transition from gas phase to fluid interior. Mostly H; 15 % He, a few % Methane, ammonia and water vapor. Optical view from Earth: Blue color of methane Cloud structures only visible after artificial computer enhancement of optical images taken from Voyager spacecraft.

The Structure of Uranus’ Atmosphere Only one layer of Methane clouds (in contrast to 3 cloud layers on Jupiter and Saturn). Cloud layer is very deep in Uranus’ atmosphere. Uranus’ cloud layer difficult to see because of thick atmosphere above it.

The Interior of Uranus Average density ≈ 1.29 g/cm 3 → larger portion of rock and ice than Jupiter and Saturn. Ices of water, methane, and ammonia, mixed with hydrogen and silicates

Is the Earth’s magnetic north pole exactly in line with the north pole of its rotation? :10 0 of Yes. 2.No, the magnetic north pole is slightly offset (in the direction of Canada). 3.No, it is substantially offset (near central Europe). 4.No, it is completely independent of the rotation: The magnetic north pole is actually on the Equator.

The Magnetic Field of Uranus No metallic core → no magnetic field was expected. But actually, magnetic field of ~ 75 % of Earth’s magnetic field strength was discovered: Offset from center: ~ 30 % of planet’s radius! Inclined by ~ 60 o against axis of rotation. Possibly due to dynamo in liquid- water/ammonia/methane solution in Uranus’ interior.

The Moons of Uranus Oberon Umbriel Ariel Miranda Titania D = 1550 km 480 km 1610 km 1190 km 1160 km

Would you expect the moons of Uranus to be volcanically active? :10 0 of Yes, because their interiors should be very hot due to tidal interactions with Uranus. 2.Yes, because their interiors should be very hot due to radioactive decay of heavy elements. 3.Yes, because they might be heavily bombarded by meteorites. 4.No, because they might be very cold and have a very deep crust and solid mantle region.

The Moons of Uranus Oberon Umbriel Ariel Miranda Titania D = 1550 km 480 km 1610 km 1190 km 1160 km Mostly inactive; heavily cratered surfaces.

Neptune Discovered in 1846 at position predicted from gravitational disturbances on Uranus’ orbit.

Why does Neptune appear blue? :10 0 of It’s the natural color of hydrogen in the Neptune’s atmosphere. 2.It’s the natural color of methane in the Neptune’s atmosphere. 3.It’s the natural color of ammonia in the Neptune’s atmosphere. 4.Because of large-angle scattering of sunlight towards Earth (the same effect that makes our sky appear blue).

Neptune Discovered in 1846 at position predicted from gravitational disturbances on Uranus’ orbit. Blue-green color from methane in the atmosphere 4 times Earth’s diameter; 4 % smaller than Uranus

The Atmosphere of Neptune Cloud-belt structure with high-velocity winds; origin not well understood. Darker cyclonic disturbances, similar to Great Red Spot on Jupiter, but not long-lived. The “Great Dark Spot” White cloud features of methane ice crystals

The Rings of Neptune Made of dark material, visible in forward- scattered light. Interrupted between denser segments (arcs) Focused by small shepherd moons embedded in the ring structure. Ring material must be regularly re-supplied by dust from meteorite impacts on the moons.

When viewed from the North, all planets and moons are orbiting … :10 0 of Clockwise. 2.Counterclockwise. 3.All counterclockwise, except for Venus which orbits clockwise. 4.Some clockwise, some counterclockwise. There’s no preferred sense of orbital motion. 5.Planets are orbiting clockwise around the sun; moons are orbiting counterclockwise around their planets.

The Moons of Neptune Two moons (Triton and Nereid) visible from Earth; 6 more discovered by Voyager 2 Unusual orbits: Triton: Only satellite in the solar system orbiting clockwise, i.e. “backward”. Nereid: Highly eccentric orbit; very long orbital period (359.4 d).

The Surface of Triton → Triton can hold a tenuous atmosphere of nitrogen and some methane; 10 5 times less dense than Earth’s atmosphere. Very low temperature (34.5 K) Surface composed of ices: nitrogen, methane, carbon monoxide, carbon dioxide. Possibly cyclic nitrogen ice deposition and re-vaporizing on Triton’s south pole, similar to CO 2 ice polar cap cycles on Mars.

The Surface of Triton (II) Ongoing surface activity: Surface features probably not more than 100 million years old. Large basins might have been flooded multiple times by liquids from the interior.

Pluto and Charon Hubble-Space- Telescope image Size of Earth to scale Pluto: discovered 1930 Average distance from the sun: ≈ 40 AU Orbit highly inclined against plane of the solar system Most eccentric planetary orbit in the solar system; part of orbit is inside Neptune’s orbit! orbit is inside Neptune’s orbit! Moon Charon about half the size of Pluto; occasional eclipses of Pluto and Charon eclipses of Pluto and Charon

Would you think that Pluto and Charon have a similar history as the four gas giants? :10 0 of Yes, because they are in the same region of the solar system. 2.Yes, because they are very similar in size and composition to the gas giants. 3.Both 1. and 2. are true. 4.No, because they are very different in size and composition from the gas giants. 5.No, because they have very unusual orbits. 6.Both 4. and 5. are true.

The Origin of Pluto and Charon Probably very different history than neighboring Jovian planets. Modern theory: Pluto and Charon members of Kuiper belt of small, icy objects. Collision between Pluto and Charon may have caused the peculiar orbital patterns and large inclination of Pluto’s rotation axis.

The Tenth “Planet” Discovered on Jan. 8, 2005 Bigger than Pluto Currently 97 AU from the sun (3 times further than Pluto) Composition and surface structure probably similar to Pluto’s