Transcript Planetary Science

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 ‘xray’ 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
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¼ the size of Earth;
1/ the mass of Earth;
80
1/ the gravitational pull of Earth;
6
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!)