Transcript Wednesday, March 26 - Otterbein University

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
Quadrantids (QUA)
Lyrids (LYR)
Eta Aquarids
Beta Taurids
Delta Aquarids
Perseids (PER)
Draconids
Orionids (ORI)
Taurids
Leonids (LEO)
Geminids (GEM)
Duration
Dec. 28-Jan. 7
Apr. 16-25
Apr. 21-May 12
June 30
July 25-31
Aug. 10-14
Oct. 6-10
Oct. 15-29
Oct.12- Dec 2
Nov. 14-20
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
• Barringer Crater, AZ
0.8 mi diameter, 200
yd deep; produced
by impact about
25,000 years ago
• Quebec's Manicouagan
Reservoir. Large
meteorite landed about
200 million years ago. The
lake, 45 miles in diameter,
now fills the ring.
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: ¼
Earth/Moon mass: 1/81
Earth-Moon distance:
384,000 km
Features of the Earth & Moon
• Mass: Earth: 6  1024 kg
• Radius: Earth: 6400 km
• Density: Earth: 5500 kg/m3
Moon: 1/81 Earth’s
Moon: 1/4 Earth’s ra
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
• 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
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
Runoff channels
Outflow 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 bacterialike 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