Astro10 Lecture09

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The Jovian Planets: 

The Jovian Planets

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Unlike terrestrial planets, Jovian planets are made of gas and liquid. Jupiter and Saturn: mostly hydrogen and helium, with a few percent hydrogen compounds and a small fraction of rock and metal. Uranus and Neptune: Less than half the mass is H and He, with most of the composition made of hydrogen compounds such as water, ammonia, methane.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics The Jovian planets formed beyond the frost line and were thought to have grown from planetesimals of about the same mass – 10 Earth masses. At greater distances, it took longer for small particles to accrete into large, icy planetesimals with gravity strong enough to pull in more material from the solar nebula. Jupiter was first to form and was able to pull in the most material followed by Saturn and Uranus-Neptune. Neptune is slightly more massive and denser than Uranus which suggests it formed from a slightly more massive ice-rich planetesimal.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Density Differences Saturn is considerably less dense than the other planets. This makes sense if you compare what each planet is made of: Uranus and Neptune have less % of H and He than Saturn. But then Jupiter should be the least dense of all! But it is not because its large gravity compresses the atmosphere. This also, explains why Jupiter is only slightly larger in radius than Saturn

Lecture 11: The Jovian Planets Composition, Structure, and Dynamics: 

Lecture 11: The Jovian Planets Composition, Structure, and Dynamics Shape of the Planets The Jovian planets are non-spherical and have larger circumferences around their equators than around the great circles through the poles. Saturn is the most oblate as it is about 10% wider than it is tall. The strong gravity should make these large worlds spherical but rapid rotation makes the equatorial region bulge out.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Inside Jupiter The Galileo probe penetrated to a depth of 200 km (or 0.3% of Jupiter radius) before contact was lost. At a depth of 80–100 km, predictions indicate the temperature is Earth-like and the pressure is 10 times greater than that at the Earth’s surface. As one goes deeper in Jupiter’s atmosphere, gaseous hydrogen becomes liquid hydrogen (~7,000 km). The pressure here is 500,000 times that of the Earth surface. At ~15,000 km below the clouds, it is theorized that pressure and temperature create a state of liquid metallic hydrogen (exists only in Jupiter and Saturn). The core which contains roughly 10 Earth masses is only about the radius of the Earth (~6500 km).

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Comparing Jovian interiors Saturn is the most similar to Jupiter and has liquid metallic hydrogen too, but much deeper beneath the visible clouds. The pressures are not high enough to form liquid metallic hydrogen in Uranus and Neptune; however, hydrogen compounds reside in a layer above the central core of rock and metal.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Magnetic Fields Jupiter’s magnetic field is quite strong - nearly 20,000 times stronger than Earth’s. Jupiter’s low density and distance from Sun implies that iron is not the source of the strong magnetic field. Since hydrogen dominates and high pressures exist inside Jupiter, theorists predict that liquid metallic hydrogen is best possible generator of the magnetic field. Fast rotation period increases field strength. Jupiter collects far more charged particles than the Earth does. The other Jovian planets have smaller magnetic fields (though larger than Earth’s if compared side-by-side). Uranus and Neptune’s magnetic field is generated by the core “oceans” of hydrogen compounds, rock, and metal.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics The Atmosphere (Weather) Weather is driven on the Jovian planets by energy from the Sun and from within (plus the rotation of the planet). Internal energy (present in all but Uranus) is likely coming from the conversion of potential energy to kinetic energy as gasses are slowly falling or condensing inside these planets.

Slide10: 

Jupiter from a ground-based telescope

Slide11: 

Jupiter from Cassini: 4 October 2000 Courtesy of NASA/JPL-Caltech

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Jupiter from New Horizions: 10 February 2007 Courtesy of NASA/JPL-Caltech Red Spot Red Jr.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Clouds and Colors The Jovian planets have clouds which condense from a gas when the temperature becomes cold enough. For the Earth only one gas – water vapor – can condense. For Jupiter, from high to low altitude: ammonia, ammonium hydrosulfide, and water condense to form cloud layers, so most of the time we see ammonia clouds. This happens at about 30 to 100 km below the upper cloud tops. For Saturn the same layers form but deeper in the atmosphere (200 km below) and farther apart . Why? Saturn is colder and has weaker gravity. For Uranus and Neptune, methane clouds dominate the atmosphere. These absorb red light very well and make the planets blue.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Storms on Jupiter Jupiter’s Giant Red Spot, first seen in the mid-1600s, has lasted for over 300 years (or at least 150 years). The Giant Red Spot is a high-pressure storm system that rotates counterclockwise every 6 days. The red spot is 40,000 km long and 15,000 km across, larger than the 13,000-km diameter Earth. Cause of red color is still debated. Several (12) zones and belts can be seen too. This banded structure is due to the Coriolis effect and rapid rotation. A New Red Spot? Oval BA formed in 2000 when three smaller spots collided and merged. White in November 2005, brown in December 2005, and then red in February 2006. As of March 2006, Red Jr. is about half the size of the Great Red Spot.

The Jovian Planets Composition, Structure, and Dynamics: 

The Jovian Planets Composition, Structure, and Dynamics Weather on other Jovian planets Saturn has zone and belts which are harder to see since they are deeper in the atmosphere Uranus had nearly no clouds when Voyager passed in 1986, but Earth observations has shown more weather when northern “spring” comes to Uranus. Neptune had a Great Dark Spot seen by Voyager (1989) but it has since disappeared.

Slide16: 

Courtesy of NASA/JPL-Caltech Picture from Cassini: 9 February 2004 Cassini arrived 1 July 2004 http://saturn.jpl.nasa.gov

Slide17: 

Cassini Close-up of Saturnian Atmosphere l=727 nm contrast enhanced http://saturn.jpl.nasa.gov

Slide18: 

Voyager’s Uranus (1986) Normal Enhanced

Slide19: 

Keck’s Uranus (2004) Rings and planet taken with separate exposures

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Atmospheric Notes Neptune’s winds - driven by an internal heat source - reach speeds of 2200 km/hr (1300 mph).

The Jovian Planets Jupiter’s Moons: 

The Jovian Planets Jupiter’s Moons Jupiter’s Moons Jupiter’s family of 63 moons can be divided into 3 groups: Outer moons, eccentric orbits, many retrograde, dark surfaces, captured asteroids. 4 inner moons orbit very close to Jupiter and are probably fragmented moonlets (form and shape Jupiter’s ring). 4 Galilean moons, nearly circular orbits, smallest is 5,000 times more massive than the largest of the other moons.

Slide22: 

The Galilean satellites and Earth as compared to Jupiter

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Io Europa Ganymede Callisto Size of Earth’s Moon Older Younger Closer to Jupiter Further to Jupiter Dense Less Dense Surface age determined by crater counts

Slide24: 

Callisto

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Ganymede Notice grooved terrain on surface due to faults

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Water beneath surface? Surface cracked and recently reshaped Natural color Europa VIS-IR comp. Albedo

Slide27: 

Io Surface covered with sulfur(?) compounds

Slide29: 

Volcanoes on Io How? Should have cooler interior than Mercury and Mars (smaller object). Io’s elliptical orbit forced by resonance with Europa and Ganymede causes differential tidal heating. Io is tidally distorted more when closer to Jupiter than farther away. This constant flexing heats the interior. Spewed material from volcanoes forms torus of sodium(?) around Jupiter (Io Torus). Io during eclipse The Jovian Planets Jupiter’s Moons

Slide30: 

Resonances Previous examples: spin-orbit Moon (1:1) around Earth, Mercury (3:2) around Sun New examples: spin-orbit All other major satellites to parent planet (1:1) New examples: orbit-orbit Io-Europa (2:1) Europa-Ganymede (2:1) Later, in Saturn’s rings: Mimas-Cassini Division (2:1) The Jovian Planets Jupiter’s Moons

The Jovian Planets Saturn’s Moons: 

The Jovian Planets Saturn’s Moons Moons of Saturn Saturn has 60 moons, second only to Jupiter in number. Major moons include (from largest to smallest): Titan (second largest moon in the Solar System), Rhea, Iapetus, Dione, Tethys, Enceladus and Mimas.

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Rhea Mimas Enceladus Some Moons of Saturn

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Enceladus Enceladus has a very shiny surface (albedo = 0.9) and has just been discovered to have a “significant” atmosphere (which must be replenished) False-color image of anti-Saturn hemisphere Close-up of surface

Slide34: 

Tethys Dione

Slide35: 

Phoebe Phoebe enlarged Iapetus (the two toned moon) Hyperion (next page too)

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Hyperion

The Jovian Planets Saturn’s Moons: 

The Jovian Planets Saturn’s Moons Titan Titan may be the most interesting moon in the solar system because it has an atmosphere (How?). It is composed mostly of nitrogen with 1% methane and a trace of argon. When sunlight strikes methane, it can cause the formation of organic molecules, which are a known precursor to life.

Slide38: 

Titan Rhea

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Titan from Cassini visible near-infrared Next Encounter: 19 November 2007

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Titan as seen by Cassini Oct. 26, 2004 Picture from Huygens Probe on the surface of Titan (Jan 15, 2005 Polarized infrared light

Slide41: 

Global view of Titan

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Erosion features on Titan Huygens decent image 16.2 km above Titan Cassini’s Synthetic Aperature Radar image 2,000 km away Lakes Crater?

The Jovian Planets Uranus’s Moons: 

The Jovian Planets Uranus’s Moons Uranus’s Moons Five moons were known before Voyager (Miranda, Ariel, Umbriel, Titania, Oberon); now 22 more are known (total = 27). Many moons named for Shakesperian characters. All the moons appear to be low-density, icy worlds (but they appear to have had been more active than the Saturnian satellites of a similar size). The innermost, Miranda, is perhaps the strangest looking object in the solar system. It appears as if it were torn apart by a great collision and then reassembled.

The Jovian Planets Neptune’s Moons: 

The Jovian Planets Neptune’s Moons Neptune’s Moons Before Voyager 2, Neptune was known to have 2 moons; 13 moons are now known. Triton, Neptune’s largest moon, is the only major moon to revolve around a planet in a clockwise (retrograde) direction. Causes significant enough tides on Triton. Triton is also tilted 23 deg relative to Neptune’s equator Triton has a very thin atmosphere of N2 and CH4.

Slide45: 

Triton

The Jovian Planets Neptune’s Moons: 

The Jovian Planets Neptune’s Moons Triton has a light-colored surface composed of water ice with some nitrogen and methane frost. Its surface appears young, with few craters and active geyser-type volcanoes observed (nitrogen ice and carbon compounds). Triton’s active volcanism is probably due to internal heating from tides, heating from the Sun or internal residual heat.

The Jovian Planets Planetary Rings - Saturn: 

The Jovian Planets Planetary Rings - Saturn Planetary Rings Saturn’s rings are very thin, in some cases less than 100 meters thick. The rings are not solid sheets but are made up of small particles of water ice or water-ice mixed with dust. Three distinct rings are visible from Earth, and were named (outer to inner) A, B, and C.

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Saturn from Earth Voyager leaving Saturn Voyager approaching Saturn

The Jovian Planets Planetary Rings - Saturn: 

The Jovian Planets Planetary Rings - Saturn The largest division between rings is known as the Cassini division. This space is caused largely by the gravity of Mimas acting synchronously (2:1 resonance) on the orbital path of nearby ring particles. Some other ring features are explained by the presence of small shepherd moons. Mimas

Slide51: 

Close-up of Main Rings Cassini Division B Ring A Ring C Ring True

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Cassini View of the main rings in true color A B C Cassini Division Shadows

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The F ring: Confined by Shepherd Satellites Pandora and Prometheus The A ring Cassini Voyager

The Jovian Planets Planetary Rings - Saturn: 

The Jovian Planets Planetary Rings - Saturn The Origin of Rings Saturn’s rings are probably about 100 million years old. The origin of Saturn’s rings is not well understood, but is thought to be the result of: A close-orbiting, icy moon that shattered in a collision with an asteroid . A large comet which got too close to Saturn (much like Shoemaker-Levy 9 did at Jupiter in 1994). Rings around the Jovian planets are not billions of years old and must be replaced or renewed on a much smaller time scale. Tidal forces are greater on a moon in orbit close to a planet than they are on a moon in an orbit farther out.

The Jovian Planets Saturn’s Rings: 

The Jovian Planets Saturn’s Rings Roche limit is the minimum radius at which a satellite (held together by gravitational forces) may orbit without being broken apart by tidal forces. Saturn’s rings are inside Saturn’s Roche limit, so no moons can form from the particles.

The Jovian Planets Planetary Rings - Jupiter: 

Jupiter’s Ring Voyager I discovered a thin ring (system) around Jupiter. The ring is close to Jupiter, extending to only about 1.8 planetary radii. The ring is thought to be replenished from the small moonlets within or near it. The Jovian Planets Planetary Rings - Jupiter Voyager from “behind” Jupiter

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Jupiter’s Ring

The Jovian Planets Planetary Rings - Uranus and Neptune: 

The Jovian Planets Planetary Rings - Uranus and Neptune The rings of Uranus and Neptune and are made of particles which are darker and smaller than that of Saturn. The Uranian rings are narrow, a few of which are clearly confined by shepherding moons. The Neptunian rings vary in width and are confined by resonances of some of the moons.

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The End

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