12b. saturn

34
12b. Saturn Saturn data Saturnseen from the Earth Saturnrotation & structure Saturn clouds Saturnatmospheric motions Saturn rocky cores Saturn magnetic fields Discovering Saturn’s

Upload: bandele

Post on 22-Feb-2016

110 views

Category:

Documents


0 download

DESCRIPTION

12b. Saturn. Saturn data Saturn seen from the Earth Saturn rotation & structure Saturn clouds Saturn atmospheric motions Saturn rocky cores Saturn magnetic fields Discovering Saturn ’ s rings Structure of Saturn ’ s rings Rings & shepherd satellites. Saturn Data (Table 12-2). - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: 12b. Saturn

12b. Saturn• Saturn data• Saturn seen from the

Earth• Saturn rotation & structure• Saturn clouds• Saturn atmospheric

motions• Saturn rocky cores• Saturn magnetic fields• Discovering Saturn’s rings• Structure of Saturn’s rings• Rings & shepherd satellites

Page 2: 12b. Saturn

Saturn Data (Table 12-2)

Page 3: 12b. Saturn

Saturn Data: Numbers• Diameter: 120,000.km 9.26 Earth⋅• Mass: 5.7 10⋅ 26 kg 95.3 Earth⋅• Density: 0.7 water⋅ 0.13 Earth⋅• Orbit: 1.4 10⋅ 9 km 9.53 AU• Day: 10h.13m 59s 0.43 Earth⋅• Year: 29.41 years 29.41 Earth⋅

Page 4: 12b. Saturn

Saturn Data: Special Features• Saturn is the 2nd Jovian planet from the Sun• Saturn is the 2nd largest Jovian planet• Saturn is dominated by a bright ring system• Saturn has no solid surface

– ~ 85% Jupiter’s diameter but ~ 30% Jupiter’s mass• Saturn has a bland yet dynamic atmosphere

– Great White Spot, belts & zones…• Saturn interior consists of three layers

– Atmosphere: Liquid molecular hydrogen (H2)– Mantle: Liquid metallic hydrogen (H2)– Core: “Metal” & “rock”

• Saturn has 1 large & 61 confirmed small moons– Titan has a dense, opaque 98.4% N2 atmosphere

Page 5: 12b. Saturn

Saturn’s Rings are Easily Seen• Galileo Galilei 1610

– Poor-quality telescope showed “handles” on Saturn• They disappeared by 1612• They re-appeared by 1613

– Galileo was unable to identify these features• Christiaan Huygens 1655

– Good-quality telescope showed thin, flat rings• Rings seen edge-on become invisible• Rings seen tilted become visible

• Gian Domenico Cassini 1675– Dark band between the A & B rings

Cassini division• Johann Franz Encke 1838

– Dark band within the A ringEncke gap

Page 6: 12b. Saturn

Axial Tilt Gives Different Viewpoints• Saturn’s axis is tilted ~ 27° to its orbital plane

– Rings are precisely in Saturn’s equatorial plane– Saturn orbits the Sun once in ~ 29.4 years

• Every 14.7 years, Saturn’s rings are edge-on– 1995 – 1996– 2008 – 2009– 2023 – 2024

• Every 14.7 years, Saturn’s rings are at maximum tilt– 2002 – 2003 We see the South side of the

ring system– 2015 – 2016 We see the North side of the

ring system

Page 7: 12b. Saturn

Saturn Through a 1.5 m Telescope

Page 8: 12b. Saturn

Jupiter & Saturn: A Comparison

Page 9: 12b. Saturn

Saturn’s Rings As Seen From Earth

Page 10: 12b. Saturn

Saturn’s Rings are Icy Fragments• Hypothesis

– James Clerk Maxwell

1857• Rings would be torn apart if they were a solid sheet

• Observation– James Keeler

1895• Measured Doppler effect on different parts of the rings• Confirmed that the rings obey Newton’s laws

– Saturn’s rings have an albedo of ~ 0.80• Saturn’s clouds have an albedo of ~ 0.46

– Ring particle diameters from 0.01 m to 5.00 m• Modal particle size is ~ 0.1 m in diameter

Softball

Page 11: 12b. Saturn

Details of Saturn’s Ring System

Page 12: 12b. Saturn

The Roche Limit• Context

– Applies only to objects bound by mutual gravity• Competing gravitational forces

– Simple gravity between two objects• Traditionally measured from the center of mass

– Differential gravity due to tidal forces• Traditionally measured from opposite sides

• The theoretical Roche limit– Simple & differential gravitational forces are equal

• Closer to parent object Two objects are torn apart

• Farther from parent object Two objects stay together

• The actual Roche limit– Saturn’s ring system is closer than the Roche limit

Page 13: 12b. Saturn

The Rings are Thousands of Ringlets• The main ring system

– A & B rings look like a grooved phonograph record• The Cassini division is a very wide nearly empty

band• The Encke gap is a very narrow nearly empty

band– The F ring was discovered by Pioneer 11

• Several intertwined stands ~ 10 km wide• A different perspective

– Backscattering Normal perspective from Earth• Relatively empty spaces look dark• Relatively full spaces look bright

– Forward scattering Possible from beyond Saturn• Relatively empty spaces look bright

– Few particles are available to block transmission of sunlight• Relatively full spaces look dark

– Many particles are available to block transmission of sunlight

Page 14: 12b. Saturn

Forward Scattering by Rings

Page 15: 12b. Saturn

Color Variations in Saturn’s Rings• All ring particles are very nearly pure white

– This is expected of pure ices

• Different sections of different rings exhibit color– The shades of color are very subtle

• Computer enhancement increases color saturation

– Molecules causing the color are unidentified– Ringlet orbits must be rather stable

• The colors show up in relatively wide bands

Page 16: 12b. Saturn

Enhanced Ring Color Variations

Page 17: 12b. Saturn

Saturn’s Inner Moons Affect Rings• Independent satellites Mimas

– Saturn’s moon Mimas orbits Saturn in 22.6 hours

– Cassini division particle orbits Saturn in 11.3 hours• Orbital resonance clears Cassini division particles• Resonance between Jupiter’s Io, Europa & Ganymede

• Shepherd satellites Pandora & Prometheus– These two moons shepherd F ring particles

• Imbedded satellites Pan– Pan orbits Saturn within & creates the Encke gap– Countless ringlets probably have similar satellites

• Probably < 1 km in diameter

Page 18: 12b. Saturn

The F Ring’s Two Shepherd Moons

Page 19: 12b. Saturn

Saturn’s Atmospheric Properties• Differential rotation• Much less color than Jupiter’s clouds

– Possibly caused by additional atmospheric haze• Presence of belts [falling air] & zones [rising air]• Occasional short-lived storms

– “White spots”• Three cloud layers farther apart than Jupiter’s

– Ammonia ice crystals– Ammonium hydrosulfide ice crystals– Water ice crystals

• Extremely high wind speeds– ~ 500 m . sec–1 near the equator– ~ 67% the speed of sound in Saturn’s atmosphere

Page 20: 12b. Saturn

Saturn’s True Colors Seen By HST

1994

Page 21: 12b. Saturn

Cloud Layers of Jupiter & Saturn

Page 22: 12b. Saturn

Saturn’s Interior is Like Jupiter’s• Saturn is the most oblate of all the planets

– ~ 9.8% shorter polar than equatorial diameter– Greater if Jupiter & Saturn had same structures

• Jupiter has ~ 2.6% of its mass in a rocky core• Saturn has ~ 10% of its mass in a rocky core

• Saturn has relatively little liquid metallic H2

– Too little mass to compress very much hydrogen• Saturn’s magnetosphere is relatively weak

– Not enough liquid metallic hydrogen– Saturn has no volcanic satellite

• Few sulfur ions in Saturn’s magnetosphere

Page 23: 12b. Saturn

The Interiors of Jupiter & Saturn

Page 24: 12b. Saturn

Auroral Rings on Saturn From HST

Page 25: 12b. Saturn

Saturn Generates Its Own Energy• Two observations

– Saturn emits more energy than it gets from the Sun• ~ 25% more per kg than Jupiter

– Saturn’s atmosphere is distinctly deficient in helium• 13.6% for Jupiter but only 3.3% for Saturn

• One possible process– Helium is cold enough the condense in Saturn’s air

• Helium precipitation falls to lower levers– Gravitational energy is converted into heat energy– Helium permanently removed from Saturn’s upper atmosphere

– Energy conversion equals Saturn’s excess heat

Page 26: 12b. Saturn

Saturn’s Moon Titan’s Atmosphere• Titan data

– Second largest Solar System satellite

5,150 km– Only satellite with a substantial atmosphere

• Gerard Kuiper detects CH4 absorption spectrum

1944• Overall composition is ~ 98.4% N2• ~ 1.5 x Earth’s pressure with ~ 10 x Earth’s gas

– Weaker gravity does not compress gas as much– Titan is perpetually cloud covered

• Titan’s surface comparable to full moonlight on Earth• Some implications

– Hydrocarbon fog & rain obscure surface visibility– Surface may be covered with hydrocarbon “goo”– Surface has liquid hydrocarbon oceans

• InfraRed radiation penetrates clouds to “see” surface

Page 27: 12b. Saturn

Saturn & Titan’s Atmosphere

Page 28: 12b. Saturn

Hydrocarbon Seas on Titan

Page 29: 12b. Saturn

Saturn’s Six Icy-Surfaced Satellites• Mimas & Enceladus

– Small

• Tethys & Dione– Medium

• Rhea & Iapetus– Large

Page 30: 12b. Saturn

Cassini/Huygens on Earth

Page 31: 12b. Saturn

Cassini/Huygens at Saturn

Page 32: 12b. Saturn

Cassini & Huygens Explore Saturn• The overall mission

– Launched 15 Oct. 1997 by a Titan IVB/Centaur• Largest, heaviest, most complex interplanetary spacecraft

– Multiple gravity-assist maneuvers• Earth Venus Venus Earth Jupiter Saturn⇒ ⇒ ⇒ ⇒ ⇒

• The Cassini orbiter– Science observations began

1 Jan 2004– Saturn Orbit Insertion

30 Jun 2004– Nominal end of science observations

1 Jul 2008– Extended mission

? ? ? ? ?• The Huygens lander

– Lander separated from orbiter

25 Dec 2004– Lander entered Titan’s atmosphere

14 Jan 2005

Page 33: 12b. Saturn

The Huygens Scientific Instruments•  Aerosol Collector & Pyrolyser (ACP)

– Collect aerosols for chemical-composition analyses• Descent Imager/Spectral Radiometer (DISR)

– Images & spectral measurements over a wide spectral range– A lamp in order to acquire spectra of the surface material

• Doppler Wind Experiment (DWE)– Uses radio signals to deduce atmospheric wind properties

• Gas Chromatograph & Mass Spectrometer (GCMS)– Identify & quantify various atmospheric constituents– High-altitude gas analyses

• Huygens Atmosphere Structure Instrument (HASI)– Physical & electrical properties of the atmosphere

• Surface Science Package (SSP)– Physical properties & composition of the surface

Page 34: 12b. Saturn

• Saturn data– ~ 69% as dense as water

• Saturn would float in a huge ocean– ~ 30% Jupiter’s mass

• Proportionally larger rocky core– ~ 85% Jupiter’s diameter

• Weaker gravity can’t compress gas• Visually dominated by the ring system

– Countless mini-moons in “ringlets”• Very subtle colors in wide bands

– The Roche limit• Tidal force = Mutual gravity force• Can break up comets & moons

• Saturn’s moons– Independent, shepherd & imbedded

• Almost all affect ringlet structures– Titan is largest in the Solar System

• Dense & perpetually cloud-covered• Very rich in hydrocarbons

• Saturn’s atmosphere– Same cloud layers as Jupiter

• Spread out much more vertically Noticeably deficient in helium

• Helium precipitation falls downward– Extremely high wind speeds

• More excess heat per kg than Jupiter• Produced by falling helium droplets

• Saturn’s interior– Generally similar to Jupiter

• Much less liquid metallic hydrogen• Much weaker magnetosphere

• Saturn’s moon Titan– Target of the Huygens probe

• Enter Titan’s atmosphere Nov. 2004

Important Concepts