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Cosmic
Collisions
The sky is falling.
The sky is falling.
-Chicken Little
Leonids Meteor Shower: Tuesday
morning Nov.19, 3:36 AM
http://leonid.arc.nasa.gov/1998.html
Lecture on Saturday, November 16th on
meteor showers by Dr. Flemming at
Flandrau Planetarium (6$)
The Peekskill Meteorite
Eyewitness accounts indicate that the fireball associated with the Peekskill
meteorite appeared over West Virginia on October 9th, 1992 at 23:48 UT. The
fireball traveled in the northeasterly direction, was as bright as a full moon, and
eventually came to Earth in Peekskill, N.Y. The meteorite had a mass of 12.4
kg and damaged a car when it hit the Earth.
Watch the Movie
Craters on the Moon
This ranger image of the
moon shows that some
regions are relatively
smooth and other
heavily cratered.
Close-up View of Craters on the
Moon
This close-up view of the
lunar highlands shows
that the surface is
covered with craters of
varying sizes.
Barringer (Meteor) Crater
The best preserved crater on
Earth is ~200 miles north of here
(30 miles east of Flagstaff).
The crater is 1 mile in diameter,
about 570 feet deep.
It was formed 20,000 years ago
by the impact of a nickle-iron
meteorite roughly 150 feet
across and weighing 300,000
tons.
More info on the Barringer crater can be
found at http://www.barringercrater.com/
An energy equivalent to
explosion of 20,000 kilotons of
TNT was released in the impact
.
Barringer Crater in Northern
Arizona
Gene Shoemaker on the crater edge.
Manicougan Crater
The Manicouagan crater lies
in northern Quebec, Canada.
It is one of the largest known,
with a diameter of about 100
km. The crater is a multiplering structure, but the feature
that shows up best in this
Landsat satellite photo is the
inner ring, which is occupied
by lake Manicouagan with an
outer diameter of about 70
km. The impact occurred 214
million years ago. The
asteroid probably had a
diameter of about 5 km.
Impact Structures around the World
The Asteroid Belt
This figure shows a view of
the solar system from high
above it. The dots
represent the largest
asteriods where they would
be found on March 19,
1993.
The size of the dots used to
represent asteroids is
exaggerated to make them
visible. Even though the
figure looks crowded, real
asteroids are very small
relative to the space
between them.
Figure adapted from Mark Sykes,
Steward Observatory
Some Orbits cross that of the Earth
These are called Near Earth Asteroids
NEAR SHOEMAKER AND EROS
Feb. 17, 1996. NEAR successfully launches
from Cape Canaveral on a Delta-2 rocket.
Dec. 20, 1998. NEAR's initial Eros
rendezvous maneuver aborts moments after
thruster firing starts. Contact with Mission
Operations is regained after 27 hours of
silence, but the rendezvous has been lost.
Feb. 14, 2000. NEAR enters an orbit 207
miles (333 kilometers) from the center of Eros,
and the yearlong encounter begins.
February 2001. Mission ends with the descent
to the surface.
Eros, one of the largest near-Earth asteroids,
lies in between an ordinary chondrite and a
stony iron meteorite – thus it has probably
been little altered in its lifetime
For more info visit http://near.jhuapl.edu/
NEAR SHOEMAKER HIGH
RESOLUTION IMAGES OF EROS
Play the Movie
NEAR Shoemaker captured this movie on December 3-4, 2000, while in
orbit 200 kilometers (125 miles) from the center of Eros. Covering a full
rotation of the 21-mile-long asteroid, the movie opens with a look at one of
Eros' battered ends and a sweep over the saddle-shaped depression
named Himeros. The sequence then includes a view of Shoemaker Regio
- the large boulder patch beside Himeros - before swinging over the
opposite end and providing a stunning view of a sunset inside Psyche, the
asteroid's large, 5-kilometer (3-mile) impact crater. The movie wraps up
with a return to the asteroid's heavily cratered tip.
NEAR-SHOEMAKER’S
FINAL APPROACH
Play the Movie
NEAR Shoemaker's multispectral imager (MSI) captured the images in this
movie during the spacecraft's controlled descent to Eros on February 12,
2001. Starting from just over 3 miles (5 kilometers) above the surface, the
camera moves over cracked and jagged rocks, boulder patches, craters filled
with dust and debris, and mysterious areas where the surface seems to have
collapsed. The final frame, taken 422 feet (128 meters) above Eros, shows
features a few inches across. The black area across the bottom of the last
frame indicates a loss of signal, as the spacecraft landed during
transmission.
THE IMPACT OF COMET
SHOEMAKER-LEVY 9 WITH JUPITER
In 1993, a comet was observed near Jupiter. Orbital calculations revealed
that it would collide with Jupiter in July 1994. Subsequent observations
revealed that the tidal forces of Jupiter had split the comet into 21 fragments.
For more information http://www.jpl.nasa.gov/sl9/sl9.html
HST observations show a plume rising
above the fragment G impact site
Debris in the Jovian Atmosphere.
A cloud of debris
spread out from the
G impact site
What would happen if a comet
fragment this size hit the Earth?
On the
morning of
June 30,
1908, a
tremendous
explosion
occurred in a
remote area
of central
Siberia near
the Tunguska
river. Seismic
vibrations
were
recorded by
sensitive
instruments
1000 km
away.
Tunguska
On the morning of June 30, 1908
a tremendous explosion occurred
in a remote area of central
Siberia near the Tunguska river.
Seismic vibrations were recorded
by sensitive instruments 1000 km
away. At 500 km, observers
reported "deafening bangs" and
a fiery cloud on the horizon.
About 170 km from the
explosion, the object was seen in
the cloudless, daytime sky as a
brilliant fireball. At distances
around 60 km, people were
thrown to the ground or even
knocked unconscious;
windows were broken and crockery knocked off shelves. Reindeer herders asleep
in their tents in several camps about 30 km from the site. They were blown into
the air and knocked unconscious.
http://www.psi.edu/projects/siberia/siberia.html
by William Hartmann.
Tunguska region in 1938:
Portion of one of the photos from Kulik's aerial photographic survey (1938)
of the Tunguska region. The parallel fallen trees indicate the direction of the
blast wave.
http://www-th.bo.infn.it/tunguska/.
Tunguska Today
What Happened?
The impact of a stony
meteorite about 60 km in
diameter.
The meteorite did not hit
the Earth but exploded
above the ground.
The blast was equivalent to
the explosion of 40,000
kilotons of TNT (2000
Hiroshima bombs).
Shown to the left is the size
of the area devastated by
the blast.
K-T Boundary Strata
In 1980, a thin sedimentary layer of remarkable composition was discovered.
Iridium and the K-T Boundary
Iridium is rare in Earth’s
crust but common in
meteorites. Iridium
dissolves in iron and is
thought to be locked up
in Earth’s core.
It’s high abundance at
the K-T boundary is
evidence for a meteorite
impact.
Meteorite needed: one
10 km in diameter.
The Chicxulub Impact
Size of
impactor
needed:
10 km in
diameter.
For more information on the Chicxulub Impact and the K-T boundary check out
http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html
Radiometric Dating Places the Chicxulub
Impact precisely at the Boundary between
the Cretaceous and Tertiary Periods
This is the K-T Boundary
65 million years ago
K is for Kreide, meaning chalk in German for
the limestone deposits found near this depth.
The Chicxulub Impact
An asteroid 10 km in diameter hit the Earth 65 million
yrs ago.
An explosion of 100 million megatons of TNT, 6 million
times more energetic than the 1980 Mount St. Helens
volcanic eruption, 5 billion nuclear bombs occurred. It
dwarfs anything civilization has experienced.
It carved a crater 100 km in diameter.
It launched dust into the atmosphere blotting out
sunlight for weeks to months.
The shock produced 10 magnitude earthquakes.
K-T
Impact
These data come from counting the number of species in marine sediments.
Large extinction events have happened several times in the Earth’s history.
About 75% of the species on the planet disappeared at the K-T boundary.
What are the probabilities?
From Hartman and Impey
From
Hartman &
Impey
Something to think about
Summary
• Large impacts on Earth can alter flora and fauna.
• Strong evidence indicates that an impact caused the
extinction of species 65 myr ago.
• This evidence is contained in the composition of the rock
layer laid down during this era. Additional evidence
comes from the 100 km crater in Mexico dating back to
K-T boundary.
• Meteorites are bits of rubble (asteroids or comets) that
orbit the Sun, having either never formed into planets or
having been broken off of planets.
• Most rocks that hit Earth are small and inconsequential.