Chapter 891011 Part 2

Planets in GeneralStandard Plane

Comparative Planetology

Hartmann: Chapters 8 Planetary Interiors 9 Planetary Surfaces 10 Planetary Surfaces 11 Planetary Atmospheres

Comparative Planetology

Formation historyInterior geological activityAtmosphere atmospheric activityMagnetic field magnetic field activity

Role of Planetary SizeRole of Distance from SunRole of Rotation

Comparative Planetology

Formation historyInterior geological activity

Four basic properties of a planet: mass diameter mean density surface rock properties

Basic concept is to use the surface features & materials as observational boundary conditions & then reason out the interior of the planet based on our knowledge of how these materials behave under high pressure and how resulting surface features are formed.

Processes that Shape Surfaces

A. Impact cratering Impacts by asteroids or comets

B. Volcanism Eruption of molten rock onto surface

C. Tectonics Disruption of a planet’s surface by internal

stresses

D. Erosion Surface changes made by wind, water, or ice

CratersVolcanoesCliffsMountainsPlainsIce CapsMagnetic fieldAxis tilt

Impact CrateringVolcanism (lava, outgassing)CliffsMountains tectonicsPlainsIce CapsMagnetic fieldRotationDistance from Sun

Heating /Cooling of InteriorErosion (water, ice, wind, debris)

Comparative Planetology

Core, Mantle, Crust, Atmosphere

All terrestrial planets have a similar structure:

… a liquid core

… a mantle of molten lava

… a crust od solid, low-density rocks

… an atmosphere (large range of compositions and pressures)

Source of volcanism ….

Shield Volcanoes

Shield volcanoes are found above

hot spots.

Fluid magma chamber, from which lava erupts repeatedly through surface layers above.

Shield Volcanoes and Plate tectonics

Tectonic plates moving over hot spots producing shield volcanoes result in chains of volcanoes

Example: The Hawaiian Islands

All volcanoes on Venus and Mars are shield volcanoes

Tectonic plates DO NOT occur on Venus and Mars

This is beginning to look to be true for Mercury, too.

Volcanism appears to be responsible for formation of Mercury’s widespread plains

2009

Pancake domes are volcanoes that erupted thick molten rock.

~25 km in diameter, but only 1-2 km high.

Similar to shield volcanoes in Hawaii, but thicker lava.

Volcanoes on Venus

Sapas Mons (radar image)

2 lava-filled calderas~ 400 km (250 miles)

Lava flows

Many volcanoes,including both shield volcanoes and stratovolcanoes

Volcanoes on Mars

ValleysOlympus Mons

Highest and largest volcano in the Solar System.

Tharsis volcanoes

NASA

Venus is the only planet known to have coronae.(concentric tectonic stretch marks formed by hot rising plumes from the mantle) outward pressure from upwelling mantle material

300 km across

Coronae: Circular bulges formed by volcanic activity

Jupiter’s Moons

64 known; new ones are still being discovered.

Four largest moons already discovered by Galileo: The Galilean moons

Io Europa Ganymede Callisto

Io: Bursting Energy --> Volcanic Activity

Io Europa Ganymede Callisto

Ganymede: A Hidden PastLargest of the 4 Galilean moons.

• Av. density = 1.9 g/cm3

•Rocky core•Ice-rich mantle•Crust of ice

Bright terrain probably formed through flooding

when surface broke

Ganymede• Largest moon in the solar

system• Clear evidence of geological

activity • Tidal heating plus heat from

radio-active decay?

Io Europa Ganymede Callisto

Callisto: The Ancient Face

Heavily cratered --> OLD

No metallic core: possibly silicate core

Layer of liquid water, ~ 10 km thick, ~ 100 km below surface, probably heated by radioactive decay.

Callisto

Saturn’s moon: Titan’s Surface

• Huygens probe provided first look at Titan’s surface in early 2005

• Liquid methane, “rocks” made of ice

The Moons of Uranus5 largest moons are visible from Earth.

5 largest moons all tidally locked to Uranus.

Interiors of Uranus’s Moons

Large rock cores surrounded by icy mantles.

Uranus’s Moon MirandaMost unusual of the 5 moons detected from Earth

Ovoids: Oval groove patterns, probably associated with convection currents in the mantle, but not with impacts.

20 km high cliff near the equator

Surface features are old; Miranda is no longer geologically active.

Neptune’s Moon Triton

• Similar to Pluto, but larger

• Evidence for past geological activity

Theoretical Techniques for Calculating Interior Conditions

Equation of State ( P, T, rho):

€

dP = ρg* dzand for geologists changes of state (melting and solidifyng)is important to understand minerals

Differentiation: the process by which homogeneous material gets divided into masses of different composition and physical properties

Differentiation: the process by which homogeneous material gets divided into masses of different composition and physical properties

Other Observational that Check the Models for Planet Interiors:

moment of inertia … kMR2 , k being coefficient of … {0. 1.} geometric oblateness … reflects mass distribution or departure from hydrostatic equilibrium form of gravitational field rotation rate … necessary for moment of inertia, geometric oblateness surface heat flow composition of neighbors (planets and or meteorites) magnetic field … strong field indicates a flluid core drilling and direct sampling seismic properties } Earth

A planet with a magnetic field indicates a fluidinterior in motion

• Planetary magnetic fields are produced by the motion of electrically conducting liquids inside the planet

• This mechanism is called a dynamo

• If a planet has no magnetic field, that is evidence that there is little such liquid material in the planet’s interior or that the liquid is not in a state of motion

• The magnetic fields of terrestrial planets are produced by metals such as iron in the liquid state

• The stronger fields of the Jovian planets are generated by liquid metallic hydrogen or by water with ionized molecules dissolved in it