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COMETS ANDIMPACT CRATORS

Mullard Space Science Laboratory

University College London

http://www.mssl.ucl.ac.uk

06/08/03

What is a Comet ?

Comets are small, fragile, irregularly shaped bodies composed mostly of a mixture of water ice, dust and carbon- and silicon-

based compounds.

Comets have highly elliptical orbits thatrepeatedly bring them close to the Sun

and then swing them into Space.

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Parts of a Comet

Hydrogen Cloud Ion Tail

Nucleus

ComaDust Tail

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Ingredients for the Nucleus of a Comet

1. Water

2. Ammonia

3. Sand or Fine-grained Dirt

4. Salt

5. Methane

6. Crushed Charcoal briquettes

7. Organic compounds

8. Alcohol

9. Dry Ice

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Shoemaker-Levy 9Collision with Jupiter

Date: July 16th – July 22nd 1994Diameter: 20 fragments up to 2 km

The large dark “scars” seen on the above imagewere the result of the impact of fragment G

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Tunguska Comet Impact

Area : Earth, Siberia, TunguskaDate : 7.17AM, June 30th, 1908

A mysterious explosion occurred in the skies over Siberia. This explosion was caused by the

impact and breakup of a large meteorite, at an Altitude of roughly 6km in the atmosphere.

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Chicxulub Impact Crater

Area : Earth, Mexico, Yucatan PeninsulaAge : 65 million yearsDiameter : 170 km

Thought to be the cause of the extinction of the dinosaurs !

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How is an Impact Crater Formed ?

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Two Types of Impact Crater

1) Simple Crater – Bowl-shaped, smooth-walled craters of a small size.

2) Complex Crater – Larger craters that can collapse,form terraces, central peaks, central pits, multiple rings and peak ring basins.

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Making an Impact Crater

1. Fill a pan with surface material (flour) to a depth of about 2.5cm.

2. Smooth the surface, then tap the pan to make the material settle evenly.

3. Sprinkle a fine layer of coloured material (dry paint, or powdered drink mix), evenly and completely over the surface. (Use a sieve or sifter for more uniform layering).

4. Then sprinkle a fine layer of sand or flour over the top.

5. Use different side balls and drop from different heights, and observe the impact craters produced.

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Barringer Meter Crater

Area : Earth, ArizonaAge : 49,000 yearsDiameter : 1.186 km

Simple meteorite impact crater

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Wolfe Creek Crater

Area : Earth, AustraliaAge : 300,000 yearsDiameter : 0.875 km

Simple impact crater

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Aorounga Crater

Area : Earth, ChadAge: 200 million yearsDiameter : 17 km

A buried complex crater with dark streams

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Bessel Crater

Area : MoonDiameter : 16 km

In between a simple and complex crater

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Copernicus Crater

Area : MoonAge: > 1 billion yearsDiameter : 93 km

Complex crater with central peak and rays

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Yuty Crater

Area : Mars, North HemisphereDiameter : 10 km

Complex crater with central peak and fluid flow

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Meitner Crater

Area : VenusDiameter : 150 km

3rd Largest impact feature on Venus with 2 circular rings

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What is a Meteor, a Meteoroid, a meteorite,

and an Asteroid.

• Meteor - a flash of light in the night sky due to the friction of a meteoroid passing through the atmosphere.

• Meteoroid - an interplanetary chunk of matter smaller than 1km and frequently millimeters in size.

• Meteorite – an part of a Meteoroid that survives the fall through the atmosphere and lands on the Earth.

• Asteroid – a larger chunk of rock that comes from the asteroid belt located between the orbits of Mars and Jupiter.