Planetary Science

Why?

• Since Astronomers find it difficult or impossible to visit most astronomical objects, nearby objects are examined and comparisons/extrapolations made.

Earth First

• We examine our planet for a basic knowledge of planetary processes.

Vital Statistics

• 4.5 billion years old,

• 8,000 miles in diameter,

• 6 X 1024 kg (6 million million million million kilograms),

• Orbits the sun in 365.24 days,

• Turns on its axis once every 24 hours.

Crossection:

• Thin (5-30 mile) crust

• 1800 miles of mantle (made of magma, similar to lava)

• Outer core of liquid iron

• Inner core of solid iron.

Interior examined:

• Earthquake waves make good acoustic ‘x-ray’ to probe the layers,

• Density calculations indicate heavy core,

• Magnetic fields denote iron.

Hot as Hell!

• Due to radioactive decay,

• High pressure (lots of weight squeezing in)

• Residual heat from formation, impacts

Heat Escapes

• Heat escapes from the core via convection rolls in the mantle.

• This heat causes eruptions through the crust of volcanoes and rifts.

• This energy drives Plate Tectonics

Continental Drift

• NOT floating on water like lily pads!

• Seven large plates carry the continents (not just landmass) around on the crust, skidding on the mantle.

• Where plates meet (plate boundaries) earthquakes, subduction, volcanoes.

Why Us?

• Because of the surface area to volume ratio of a large rocky planet, its internal heat takes billions of years to escape.

• Compare this with smaller rocky worlds!

Atmosphere

• Any volume of gases that surrounds a planet is called an atmosphere.

• Our mixture of O2 and N2 is called “air”.

• In an atmosphere, weather develops due to differential heating.

• Weather changes the surface of the planet as much as plate tectonics.

Look Out Below!

• Another major producer of surface features is asteroidal/cometary impact.

• This causes small and large craters, and in extreme cases, mass extinctions.

• Evidence of cratering is erased by weather, but the earth has been hit about 20 times as much as the moon.

Robert Duval or Bruce Willis?

• Neither!

• We cannot protect ourselves from impacts unless we know many years in advance.

Our Little Buddy

The Moon

Vital Statistics

• ¼ the size of Earth;

• 1/80 the mass of Earth;

• 1/6 the gravitational pull of Earth;

• About 28 days to orbit the Earth.• Always keeps one side towards us, therefore its

“day” is 28 days long.• No permanent “dark side of the moon”;• Bone dry, no atmosphere.

Formation and Age

• Almost as old as the Earth.• Formed by two impacts about 4 billion years ago.• An object about ½ the size of Earth hit our

planet, scattering debris from Earth and the impactor that gradually condensed into our moon.

• We know this because of the ratio of isotopes we found in the lunar soil WHEN WE VISITED THERE IN 1969-1973!

Tides

• Caused by differential gravity, the different gravitation pulls from the Moon on opposite sides of the Earth.

• The side that faces the Moon experiences the greatest gravitational force that causes the oceans to bulge.

• The Earth’s center feels a lesser pull that drags it away from the far side, leaving a bulge of water.

With thanks to Lock Haven University

Highs and Lows

• As the World Turns [sic] various landmasses move into these bulges and experience high tide.

• Six hours (1/4 turn) later, these same landmasses are out of a bulge and experience low tide.

Spring and Neap Tides

• When the Sun and Moon are lin a line with the Earth, the Solar Tides add to the Lunar Tides and the variation of high and low is great: Spring Tides (no seasonal meaning).

• One week later, the Sun and Moon at at right angles with the Earth, and tidal variation is small: Neap Tides.

• Solar Tides are about 1/3 Lunar Tides.

Near and Far

• The prefix “peri” means near; the prefix “ap” means far.

• Therefore perigee means nearest the Earth in orbit, and aphelion means farthest from the Sun in orbit.

• So, tides are extra big at perigee for the Moon and perihelion for the Earth.

Phases

Lunar Eclipse (safe to view)

Solar Eclipse (dangerous to view!)