Chapter Part 3 Planets in General Standard Plane Comparative Planetology Hartmann: Chapters 8 Planetary Interiors 9 Planetary Surfaces 10 Planetary Surfaces 11 Planetary Atmospheres

Comparative Planetology Formation history Interior geological activity Atmosphere atmospheric activity Magnetic field magnetic field activity Role of Planetary Size Role of Distance from Sun Role of Rotation

Comparative Planetology Formation history Interior 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

Craters Volcanoes Cliffs Mountains Plains Ice Caps Magnetic field Axis tilt Impact Cratering Volcanism (lava, outgassing) Cliffs Mountains tectonics Plains Ice Caps Magnetic field Rotation Distance from Sun Heating /Cooling of Interior Erosion (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 ….

Craters Volcanoes Cliffs Mountains Plains Ice Caps Magnetic field Axis tilt Impact Cratering Volcanism (lava, outgassing) Cliffs Mountains tectonics Plains Ice Caps Magnetic field Rotation Distance from Sun Heating /Cooling of Interior Erosion (water, ice, wind, debris) Comparative Planetology

The Highlands on the Moon Saturated with craters Older craters partially obliterated by more recent impacts … or flooded by lava flows

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Hadley Rille-Apennine mountain region at 26 deg 06 min 54 sec N, 3 deg 39 min 30 sec E on the lunar surface. The lunar module (LM) carrying astronauts David Scott and James Irwin and the lunar roving vehicle (LRV) landed on the moon on July 31,

“lobate scarps ” are long, steep curved cliffs, probably formed when Mercury shrank while cooling down Discovery Scarp

Discovery scarp 500 km long, 2 km high Mercury’s crust split and cracked as the planet cooled and shrank lobate scarps

Two Geological features on Mercury worth mentioning: 2. lobate scarps are landforms on Mercury that appear to have formed by thrust faulting and are thought to reflect global contraction due to cooling of the planet's interior (like a drying apple)

“Radargraphs” Using radar, the topography (surface features) of Venus is imaged.

Radar images showed a relatively flat Venus with some highlands; two continental-sized areas of higher elevation; …terrain is comprised of: 10% mountain, 70% upland plains, 20% lowland plains

Role of Planetary Size Role of Distance from Sun Role of Rotation Smaller worlds cool off faster and harden earlier Larger worlds remain warm inside, promoting volcanism and tectonics Larger worlds also have more erosion because their gravity retains an atmosphere

Role of Planetary Size Role of Distance from Sun Role of Rotation

Role of Planetary Size Role of Distance from Sun Role of Rotation Planets close to Sun are too hot for rain, snow, ice and so have less erosion More difficult for hot planet to retain atmosphere Planets with liquid water have most erosion Planets far from Sun are too cold for rain, limiting erosion

Habitable Zone for Constant Liquid Water in the Solar System Role of Planetary Size Role of Distance from Sun Role of Rotation

Role of Planetary Size Role of Distance from Sun Role of Rotation Planets with slower rotation have less weather and less erosion and a weak magnetic field Planets with faster rotation have more weather and more erosion and a stronger magnetic field Slow rotation Fast rotation

Other Observational that Check the Models for Planet Interiors: moment of inertia … kMR 2, 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

Craters Volcanoes Cliffs Mountains Plains Ice Caps Magnetic field Axis tilt Impact Cratering Volcanism (lava, outgassing) Cliffs Mountains tectonics Plains Ice Caps Magnetic field Rotation Distance from Sun Heating /Cooling of Interior Erosion (water, ice, wind, debris) Comparative Planetology

The Earth’s Magnetic Field is created in the same way you make an electromagnet education.gsfc.nasa.gov/nycri/units/pmarchase/ In an electromagnet the electrons move around an iron nail

A planet with a magnetic field indicates a fluid interior 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

Main Worlds with Active Magnetic Fields Strength Order: Sun, Gas giants, Earth, Mercury, Mars (remnant)

The Crust: A Thin Rock Material The Mantle: A Dense and Mostly Solid Rock Material The Outer Core: Liquid Iron and Nickel The Inner Core: Solid Iron and Nickel The Earth is made of four layers

The Iron Core of the Earth is an Electromagnet The core is surrounded by liquid Iron and Nickel As electrons flow around the core the magnetic field is produced The Earth’s rotation makes the electrons flow at very high speeds

PlanetMagnetic Field Mercury100 times weaker than Earth Venus25,000 times weaker than Earth Earth30,000 – 60,000 nT Mars5000 times weaker than Earth Jupiter20,000 times greater than Earth Saturn540 times greater than Earth Uranus40 times greater than Earth Neptune¼ that of Earth PlutoNone that we know of Magnetic Fields on Other Planets in our Solar System

Mercury Mercury has a weak magnetic field. This suggests Mercury has an iron core with liquid interior. The weak magnetic field could be the result of the slow rotation period.

Venus Venus has a very weak magnetic field. (About 25,000 times weaker than Earth’s) Venus appears to lack the necessary ingredients to generate a magnetic field (no liquid core?) Venus also has very slow rotation.

Mars Mars also has a very weak magnetic field. (About 5,000 times weaker than Earth’s) The interior of Mars appears to have cooled so much that it is no longer liquid. The volcanoes in Mars are no longer active There is no Earthquake activity on Mars

Jupiter Jupiter has a strong magnetic field. (About 20,000 times stronger than Earth’s) The Terrestrial planets generate magnetic fields from iron at the center. But Jupiter has almost no iron core. The magnetic field of Jupiter is produced by the motion of liquefied metallic hydrogen found beneath the surface.

Saturn Saturn also has a strong magnetic field. (About 540 times stronger than Earth’s) Saturn’s magnetic field is produced in the same way Jupiter’s is.

Uranus The magnetic field in Uranus is about 40 times stronger than Earth’s It is probably created in the core of the planet, with ice, rather than with iron.

Neptune The magnetic field in Uranus is about 1/4 times as strong as Earth’s It is probably created in the same way as Uranus

Pluto We do not know if Pluto has a magnetic field. Because Pluto has a small size and a slow rotation rate (1 day in Pluto = 6.4 Earth days), it does not seem likely that Pluto has a magnetic field.