Presentation on theme: "Comets Visitors from the Unknown Comets Visitors from the Unknown Mr. K., NASA/GRC/LTP Edited: Ruth Petersen Mr. K., NASA/GRC/LTP Edited: Ruth Petersen."— Presentation transcript:
Comets Visitors from the Unknown Comets Visitors from the Unknown Mr. K., NASA/GRC/LTP Edited: Ruth Petersen Mr. K., NASA/GRC/LTP Edited: Ruth Petersen
Preliminary Activities 1. Word Activity: Look up the word “COMET” in a dictionary. What is the origin of the word? Who were the people who made up this name? What did they believe about their world? 2. Science Activity: Use the www or other references to learn about the structure and composition of comets. What is the primary ingredient of most comets?
3. History Activity: In 1910, the earth actually passed through the tail of Halley’s comet. Use the www or other references to learn about what happened. What did people think was going to happen? How did they prepare? What really happened? (Hint: What are comet pills?)
Which finally cleared out to leave just the Sun & Planets (and their moons, etc.) Formation of the Solar System It began with a Nebular Gas Cloud From which developed Proto-Sun & Planets Debris Rocky Matter (Source of craters) Icy Matter (Source of comets) From which came the Sun, Planets, & Debris
Rocky Matter... What do you see happening here? What do you think that the end result will be? Can we see evidence of this kind of bombardment today?
Icy Matter... Jan Oort’s Cometary Cloud
Most comets that we see today are believed to have come from the Oort cloud. Why do you suppose they leave the cloud in the first place?
Could our sun have a dark companion? Some scientists who think “Yes” have actually named the star “Nemesis”!...
“Life History" of a Comet From the Oort Cloud Why do you suppose the tail always points away from the sun? What are the head and tail made of?
The SOHO Twins
Head Tail Toward Sun Solar Pressure Structure of a Comet The head and tail are made of materials that “evaporate” from the tiny solid nucleus. Can you find the head and tail of this comet? Which direction is the sun? Which direction is the solar pressure?.
Nucleus - Few 10’s of km Coma - May be 1000’s of km The Head of a Comet
The Tail may be Millions of km The Tail of a Comet
The Nucleus of a Comet Eruptive Jets Solid Mass 1. Eruptive jets may result in pieces of the nucleus - big and small - being broken off and thrust into space! 2. As the icy matrix evaporates, other loosely bound rocky material is liberated. 3. So … what do you think happens to all these solid pieces - the “Cometary Debris?
Have you ever watched a meteor shower? Do you ever wonder why they recur every year at the same time? Did you know that there is a connection between meteor showers and cometary debris? Can you describe the connection?
Cometary debris travels with the comet along its orbit. Planets crossing the comet’s orbit collide with the debris. The debris appears to fall out of the sky - similar to driving your car in the rain!
Now...Can you suggest a connection between meteorites and dinosaurs? What can you say about mass extinctions in general?
Large objects are believed to rain down to Earth periodically. Major impacts, such as this one, may cause drastic changes in life on Earth, including mass extinction of species.
Perhaps periodic disturbances in the Oort cloud - as by the passage in & out of a Nemesis star in an eccentric, long period orbit - result in periods of increased cometary activity throughout the solar system. Increased activity results in more large-scale collisions.
Evidence? Here are Luis and Walter Alvarez at the now famous KT boundary. Clay layer with Iridium. Cretaceous - Dinosaurs Tertiary - No Dinosaurs
Is this where the meteorite that changed dinosaur history struck the Earth? Magnetic map showing location of buried crater.
Comets come in all shapes and sizes. One might occur at any time. Remember to watch your local newspaper, check the www, or contact your local observatory or planetarium to find out when the next comet will pass close by the Earth. Remember: Watch the skies!!!
Follow-Up Activities 1. Now that you know about the dinosaurs, check out the key word, “TUNGUSKA,’ for an account of a 20th century impact in a little know region on Earth! May we still expect such impacts to happen today? 2. How would you prepare if you knew that a major comet or asteroid were going to hit the Earth?
3. Since comets are mostly water, how might we use them in the future to modify the climate of a planet such as Mars? (Hint: Use the key word, “TERRAFORMING,” to get started.) Most important of all: Remember to be safe and happy!