Studying for Exam II, etc.

• Same type of exam as first one

• Chapters covered: Sec. 0.4, Ch.1, Ch. 4, not Ch. 5

• Note: also Triangulation and Measurement covered, but not terrestrial atmospheres

• March 31 (iSkylab due!) Reading: Section 10.1 “The Solar Neighborhood” plus Warm-up

• Friday, April 4: Class canceled (Conference)

Meteor Showers – caused by comets

Radiant DurationQuadrantids (QUA) Dec. 28-Jan. 7Lyrids (LYR) Apr. 16-25Eta Aquarids Apr. 21-May 12Beta Taurids June 30Delta Aquarids July 25-31Perseids (PER) Aug. 10-14Draconids Oct. 6-10Orionids (ORI) Oct. 15-29Taurids Oct.12- Dec 2Leonids (LEO) Nov. 14-20Geminids (GEM)Dec. 6-19

Meteors, Meteroids and Meteorites

• A Meteor is a sudden strike of light in the night sky

• A Meteoroid is a small asteroid, less than 100 m in diameter

• A Meteorite is any piece of interplanetary matter that survives the passage through Earth’s atmosphere and lands on Earth’s surface

Meteors and Meteorites• Small particles that strike the atmosphere• Come from fragments of asteroids, Moon, Mars,

comets• Strike the earth all the time (“meteorites”)

– High speed means lots of energy released on impact

Impact Craters

• Quebec's Manicouagan Reservoir. Large meteorite landed about 200 million years ago. The lake, 45 miles in diameter, now fills the ring.

• Barringer Crater, AZ 0.8 mi diameter, 200 yd deep; produced by impact about 25,000 years ago

Tunguska

• ~30 m body struck Siberia in 1908

• Energy equal to that of a 10 Megaton bomb!

• Detonation above ground; several craters

Frequency of Impact Events

Formation of the Solar System• Features to explain:

– planets are far apart, not bunched together– orbits of planets are nearly circular – orbits of planets lie mostly in a single plane– directions of revolution of planets about Sun is the same, and is the

same as the direction of the Sun's rotation– directions of rotation of planets about their axes is also mostly in the

same direction as the Sun's (exceptions: Venus, Uranus, Pluto)– most moons revolve around their planets in the same direction as the

rotation of the planets– differentiation between inner (terrestrial) and outer (Jovian) planets– existence and properties of the asteroids– existence and properties of the comets

Formation of the Solar System

• Condenses from a rotating cloud of gas and dust– Conservation of angular

momentum flattens it

• Dust helps cool the nebula and acts as seeds for the clumping of matter

Formation of Planets

• Orbiting dust – planitesimals

• Planitesimals collide

• Different elements form in different regions due to temperature

• Asteroids

• Remaining gas

Structure of the Planets explained

Temperature and density of materials drop with distance to sun

Cleaning up the Solar System

• Small objects are forced out of the inner Solar System by gravitational pull of bigger planets

• Small planetesimals collide and form planets

-- or are thrown out!

The Earth-Moon System

Earth/Moon radius: ¼Earth/Moon mass: 1/81

Earth-Moon distance: 384,000 km

Features of the Earth & Moon

• Mass: Earth: 6 1024 kg Moon: 1/81 Earth’s• Radius: Earth: 6400 km Moon: 1/4 Earth’s ra• Density: Earth: 5500 kg/m3 Moon: 3300 kg/m3

– 5.5 times that of water

– About 2 times that of a rock

• Gravity: Earth: 9.8 m/s2 Moon: 1/6 Earth’s gravity

(about the same as in water)

Earth’s Atmosphere• 78% Nitrogen,

21% Oxygen, 1% Other

• Troposphere – region of weather

• Stratosphere – stable and calm

• Ionosphere – gases charged by interaction with radiation from space

Ozone Layer (O3)

• Absorbs most UV radiation from the Sun

• Hole over Antarctic– Chlorofluorocarbons

(CFC’s) – released by spray cans, refrigerators

Magnetic field/shield: Motion of Charged Particles

• Charged particles “trapped” by magnetic fields

• Origin of the Van Allen radiation belts

• Protects us!

Moon: Large-Scale Features• “Maria”

– Dark areas resembling oceans

– Plains of solidified lava– Part of the lunar mantle– About 3.2–3.9 billion years

old

• Highlands (“Terrae”)– Light-colored, resemble

continents– The lunar crust– More than 4 billion years old

The Moon – Far Side

• Can be seen by satellites only

The Mountains of the Moon

• Especially well visible near the terminator – the borderline between light and shadow

Structure of the Moon

• Also consists of crust, mantle and core

• No hydrosphere, magnetosphere or atmosphere

• Little seismic action

Tides

• Daily fluctuations in the ocean levels

• Two high and two low tides per day

• A result of the difference in gravitational pull from one side of the Earth to the other– F = G M m / R2

Lunar Craters

• Old scars from meteoroid impacts

• Lots of them; all sizes– Copernicus ~ 90

km across– Reinhold ~ 40 km

across– Also craters as

small as 0.01 mm!

Ages of the Earth and Moon• Determined by radioactive dating

– Compare amount of radioactive material with amount of decay product

– Useful isotopes: • Uranium-238 (half-life 4.5 billion years)• Uranium-235 (half-life 0.7 billion years)• For shorter time scales, Carbon-14 (5730 years)

• Oldest surface rocks on Earth (Greenland, Labrador) about 3.9 billion years old – When rocks solidified

• Lunar highlands: 4.1–4.4 billion years old– Rocks from lunar maria slightly younger, more recently melted

• Meteorites: 4.5 billion years old– Date to origin of solar system

Mercury

• Small, bright but hard to see

• About the same size as the moon

• Density about that of Earth

• Day ~ 59 Earth days• Year ~ 88 Earth days

Venus

• Bright, never very far from the sun– “Morning/Evening star”

• Similar to Earth in size and density

• Day ~ 243 Earth days (retrograde!)

• Year ~ 225 Earth days

Venus

• Very thick atmosphere, mostly CO2

• Heavy cloud cover (sulfuric acid!)– About 90 times the pressure

of Earth’s atmosphere– Very strong greenhouse

effect, surface temperature about 750 K

• No magnetic field

Surface Features

• Two large “continents”– Aphrodite Terra and

Ishtar Terra– About 8% of the

surface • Highest peaks on

Aphrodite Terra rise about 14 km above the deepest surface depression– Comparable to Earth’s

mountains

Hothouse Venus: 850 °F

Mars• Fairly bright, generally not too hard to see

• Smaller than Earth• Density similar to that

of the moon• Surface temperature

150–250 K• Day ~ 24.6 hours• Year ~ 2 Earth years• Thin atmosphere,

mostly carbon dioxide– 1/150 the pressure of

Earth’s atmosphere• Tiny magnetic field, no

magnetosphere

Mars

• Northern Hemisphere basically huge volcanic plains– Similar to lunar maria

• Valles Marineris – Martian “Grand Canyon”– 4000 km long, up to 120

km across and 7 km deep– So large that it can be seen

from Earth

Martian Volcanoes• Olympus Mons

– Largest known volcano in the solar system– 700 km across at base– Peak ~25 km high (almost 3 times as tall as Mt. Everest!)

Martian Seasons: Icecaps & Dust Storms

Martian Surface Iron gives the characteristic Mars color: rusty red!

View of Viking 1 1 m rock Sojourner

Water on Mars?

Mars Louisiana

Outflow ChannelsRunoff channels

Life on Mars?

• Giovanni Schiaparelli (1877) – observed “canali” (channels) on Martian surface

• Interpreted by Percival Lowell (and others) as irrigation canals – a sign of intelligent life

• Lowell built a large observatory near Flagstaff, AZ

(Incidentally, this enabled C. Tombaugh to find Pluto in 1930)

• Speculation became more and more fanciful– A desert world with a planet-wide irrigation system to carry

water from the polar ice caps?

– Lots of sci-fi, including H.G. Wells, Bradbury, …

• All an illusion! There are no canals…

Viking Lander Experiments (1976)

• Search for bacteria-like forms of life

• Results inconclusive at best

Atmospheric Histories

• Primary atmosphere: hydrogen, helium, methane, ammonia– Too light to “stick” to a planet unless it’s very

big Jovian Planets

• Secondary atmosphere: water, CO2, SO2, …

– Outgassed from planet interiors, a result of volcanic activity

Atmospheric Histories - Venus

• Venus is closer to Sun than Earth hotter surface

• Not a lot of liquid water on surface initially

• CO2 could not be absorbed by water, rocks because of higher temperatures

run-away Greenhouse effect: it’s hot, the greenhouse gases can’t be be stored away, it gets hotter …

Earth’s Atmospheric History

• Volcanic activity spews out water steam• Temperature range allowed water to liquify• CO2 dissolves in oceans, damping greenhouse effect • More water condenses, more CO2 is absorbed• If too cold, ice forms less cloud cover more

energy• No oxygen at this point, since it would have been

used up producing “rust”• Tertiary atmosphere: early life contributes oxygen

– 1% 800 Myrs ago, 10% 400 Myrs ago

Mars – Freezing over

• Mars once had a denser atmosphere with liquid water on the surface

• As on Earth, CO2 dissolves in liquid water• But: Mars is further away from the Sun temperature drops below freezing point

inverse greenhouse effect • permafrost forms with CO2 locked away• Mars probably lost its atmosphere because its

magnetic field collapsed, because Mars’ molten core cooled down

Greenhouse Effect

• Earth absorbs energy from the Sun and heats up

• Earth re-radiates the absorbed energy in the form of infrared radiation

• The infrared radiation is absorbed by carbon dioxide and water vapor in the atmosphere

Global Warming

• Excessively “politicized” topic

• Very complex problem scientifically

• Slow changes over long periods of time

• Sources of heating, sources of cooling themselves are temperature dependent

Data is not enough – need to understand how to interpret it correctly

Noise vs Signal, Long term vs Short term

Man-made CO2 in the Atmosphere goes up

Correlation: Temperatures rise when Carbon Dioxide levels rise

• This is true since prehistoric times