Transcript document

Pg. 62
SOME INTERESTING STUFF ABOUT IMPACTS
When we look at the Moon we see the record of
impacts on its surface.
Moon formed nearly 4.5 billion ya (YEARS AGO)
intense impacts till 3.9 billion ya
From space debris - earth must have been equally impacted.
Only a few impact craters (astroblems) survive - why?
Plate tectonics destroys them. Moon has no plate tectonics
Astro =star and blema =wound fancy term for impact crater
IS IT STILL HAPPENING TODAY?
YES - Shooting stars, meteor showers.
If hit earth= meteorite
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WHERE DOES SPACE DEBRIS COME FROM?
1. Asteroids-small bodies orbiting the sun
a) Asteroid Belt - between inner and outer planets
orbit the Sun
b) small (< 600 mi diameter) rocky metallic and icy mass
c) If all came together would create a planet only
about 1/2 size of Moon
d) may have been the 10th planet but gravity of Jupiter so
strong could not combine to make that planet-interfered
with suns gravity causes “conflict” and too energetic
field for accretion to occur
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WHERE DOES SPACE DEBRIS COME FROM?
1. Asteroids-small bodies orbiting the sun
e) rarely collide but when do may cause orbital path to
change and likely they could collide with planets
f) Apollo and Amor asteroid groups’ orbits intersect
Earth’s orbit- possibility of collision
ND pg. 457 fig. 16.7
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WHERE DOES SPACE DEBRIS COME FROM?
1. Asteroids-small bodies orbiting the sun
ADD
NEAR-Shoemaker
Space Craft
Near Earth Asteroid Rendezvous-NEAR=asteroids that
come within 121 million miles of Earth
Spent about a year orbiting and collecting
images and data WHY?
Landed on Eros just to see if they could. WHY?
PG. 62-63
WHERE DOES SPACE DEBRIS COME FROM?
1. Asteroids-small bodies orbiting the sun
g) recently determined that they are numerous small bodies
(Ida and Dactyl) weakly held together not always one
solid piece
Could be
Could ALSO be
h) they may be able to absorb large amounts of energy
without being destroyed - so much for destroying an
asteroid on a collision path!-Could explain this
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2. Comets
a) ice and rock debris - see tail as frozen outer portion
turns to vapor producing gasses and dust.
Tail lines up with solar wind so always away from
the Sun
DEMO
b) small - up to 10 mi diameter
c) trillions of them out there - most in Oort cloud
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2. Comets
ADD
Kuiper Belt
Oort Cloud
Contain short-period
orbit
comets<200years
Contain long-period
orbit comets>200
years
Flattened disk image
link
Spherical image link
Comets are “dirty
snowballs”
Comets are “dirty
snowballs”
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2. Comets
d.) many have eccentric orbits which bring them
closer to Sun (and Earth) and then track far outside
Neptune’s orbit
e.) Halley’s comet is most famous - last visit 1986
~76 year return interval
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LOTS OF METEOROIDS GET TO EARTH
1.Up to 100 billion meteoroids enter Earth’s
atmosphere EVERY 24 hoursWhat happens to them?
2.Most are small - and most burn up –
shooting stars are burning meteoroids
(< 1mm in size)
a) burn due to atmospheric friction
b) some deflected back to space
c) hit Earth’s atmosphere is like hitting a solid
(water is deadly if you jump from great heights)
This causes destruction on impact with the atmosphere.
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LOTS OF METEOROIDS GET TO EARTH
3.If large enough (>.04 ounce) when hit the ground we
call them meteorites
Can create a sonic boom when enter atmosphere
hear on Earth if meteoroid is > basketball size!
Oh yeah, and can cause injuries if fall on you
YOU HAVE GOT TO BE KIDDING ME
1954 an 8.5 lb. meteorite crashed through woman’s
House bounced off several walls and hit her.
Doesn’t happen often but when it does
BIG global impact
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IMPACT SITES
METEOR CRATER, AZ - Barringer Crater
Near Winslow AZ
Crater is 0.6 miles wide and 600 feet deep with a rim
rising 100-200 feet.
Why an impact site? How do we know? Evidence?
1)
2)
3)
4)
5)
steep-sides and closed
rim rocks tilted back
inverted stratigraphy (rock layers)
huge blocks of rock outside or crater
crater floor is shattered
6) meteorite material collected from floor
7) high Temp. and high Pressure - fused sand (tektites)
and shatter cones and shatter cone in situ
8) What else could make a round circular crater-like
thingy?
volcano and solution cavity (subsidence) but no
evidence for either
DRAWING/DEMO BEFORE AND AFTER
SUBSIDENCE/SINKHOLE
Age- 50,000 years old
Meteorite 130 feet across
Trees leveled, wildfires and dust darkened sky.
Rock material vaporized by heat energy.
Twice energy as Mt.St. Helen’s eruption.
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K/T (Cretaceous/Tertiary) Event (dinos die)
1)
2)
3)
4)
5)
6)
Evidence in clays at boundary – iridium actual plot
shocked quartz grains
melted sand spherules - tektites
microscopic diamonds commonly in meteorites
fire layers-post impact fires
ratio of iridium/osmium similar to meteorites
basically the same idea as #1
Impact Site - Chicxulub off Yucatan
Tsunami sediments related to Chicxulub found in Mexico,
TX and NJ and Carolinas!
Another link
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An Ancient Impact site in Chesapeake Bay
Evidence:
Presence of tektites
shape- defined by ejecta and seismic data
Age: 35.5 million years old
EFFECT: caused a topographic low= rivers drained toward
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Tunguska, Siberia 1980
1) meteorite exploded 5 miles above ground
WHY?-probably icy and stoney NOT metallic
2) Blast heard over 600 miles away!!
3) 37 miles away a person burned and thrown 7 feet
in air by blast
4) people 300 miles away knocked down
5) fires seen 12 miles away
6) Forest leveled about 80 million of them
7) overall very nasty - luckily no one lived close
to the area! CONSIDER THIS: What if it would have
happened over a highly populated area
Meteor was between 165-100 feet in diameter
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COULD THIS HAPPEN TODAY - sure
First Remember NEAR-Shoemaker project
WHAT ARE WE DOING ABOUT IT?
NASA has 3 funded programs to address
NEO - near earth objects
ADD
SIMPLY: they are cataloguing and assessing any
potentially dangerous asteroids/meteors
Things we could do…
1.) shoot it with a nuclear warhead. problems?
2.) Use focused solar energy to nudge out of the way.
3.) Towing/pushing with space craft. Problems?
THE TRUTH: Early Detection is key.
Interesting Article
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