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 MeteoriteEyewitness 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.

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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) CraterThe 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.

An energy equivalent to explosion of 20,000 kilotons of TNT was released in the impact .

More info on the Barringer crater can be found at http://www.barringercrater.com/

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 multiple-ring 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 BeltThis 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 EROSFeb. 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

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.

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NEAR-SHOEMAKER’S FINAL APPROACH

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.

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THE IMPACT OF COMET SHOEMAKER-LEVY 9 WITH JUPITER

For more information http://www.jpl.nasa.gov/sl9/sl9.html

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.

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.

TunguskaOn 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.htmlby 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

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

Size of impactor needed:

10 km in diameter.

Radiometric Dating Places the Chicxulub Impact precisely at the Boundary between

the Cretaceous and Tertiary Periods

This is the K-T Boundary65 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.