What are comets?

1
What are comets?
2
Learning Target for 10/19

1. I can describe the make up of comets
2. I can model a comets structure
3. I can explain why astronomers use models to
   understand celestial bodies

3
A little bit about Comets

• Questions for the video
• What is the difference between long period and
  short period comets?
• Why are some comets visible and others not?
• Why do some comets have different tails?
• How are the two tails formed?
• Why do scientists think that comets may have been
  a cause for the extinction of dinosaurs and might
  have imported water to the earth?
• http//www.neok12.com/php/watch.php?vzX700a4f7352
  6d5c7872017ftComets

4
What does Comet mean?

• from the Greek word kome, meaning "hair of the
  head
• Aristotle first used the derivation kometes to
  depict comets as "stars with hair."
• The astronomical symbol for comets (?) consists
  of a disc with a hair- like tail.

5
Comets

• Comets are small, fragile, irregularly shaped
  bodies
• composed of a mixture of non-volatile grains and
  frozen gases.
• have highly elliptical orbits that bring them
  very close to the Sun and swing them deeply into
  space, often beyond the orbit of Pluto.

6
Comet Structure

• Comet structures are diverse
• Has a surrounding cloud of diffuse material,
  called a coma usually grows in size and
  brightness as the comet approaches the Sun.
• Usually a small, bright nucleus (less than 10 km
  in diameter) is visible in the middle of the
  coma. The coma and the nucleus together
  constitute the head of the comet.

7
Anatomy of a comet
8
Physical Characteristics

• As comets approach the Sun they develop enormous
  tail that flow away from the Sun.
• When far from the Sun, the nucleus is very cold.
  These Comets are sometimes referred to as a
  "dirty snowball," since over half of their
  material is ice.

9
Why are comets important?

• Comets may be an important part of the recipe for
  making planets and may be material left over from
  solar system formation.
• Some comets may have crashed into forming planets
  adding to their water and rock
• Some believe that material from comets may have
  brought water to Earth through impacts.

10
How many Comets are their?

• The number of naked-eye comets averages to
  roughly one per year, though many of these are
  faint and unspectacular.
• When a historically bright or naked-eye comet is
  witnessed by many, it is called a Great Comet.
• Examples
• Halleys comet occurs every 75 years, last seen
  1985
• Comet McNaught, also known as the Great Comet of
  2007
• Comet Hale-Bopp seen in 1997

11
Where are comets found?

• Today, most comets are located outside our solar
  system in part of the original cloud of dust and
  gas that has remained virtually untouched for
  billions of years. These regions are referred to
  as the Oort Cloud and the Kuiper Belt.

12
Kuiper (Pronounced Kiper)Belt

• The Kuiper Belt is a region of space outside the
  orbit of Neptune.
• 30 to 50 AU from the sun
• It contains countless comets and planetesimals.

13
Oort Cloud

• The Oort cloud is the farthest from the Sun that
  you can go and still be in the Solar System.
• It is believed that most comets originate in the
  Oort cloud before "falling" toward the Sun.
• Comets with long orbital periods are not
• confined to the plan of the
• solar system.

14
Fate of Comets

• Comets have a lifetime of about 10,000 years or
  1,000 revolutions
• Eventually most of the volatile material
  contained in a comet nucleus evaporates away, and
  the comet becomes a small, dark, inert lump of
  rock or rubble that can resemble an asteroid.

15
Fate of Comets

• Comets are also known to break up into large
  fragments.
• Some comets meet a more spectacular end either
  falling into the Sun, or smashing into a planet
  or other body. These are called sungrazers.

16
How scientist use models in space science

• Scientists make scientific questions based on
  current scientific theory and observation of
  models of phenomenon. NASA missions are designed
  to answer specific questions. To answer these
  questions, scientists start with a model which
  they compare with actual observations in space.
  As new data is gathered, the model is improved if
  needed and re-tested against observations

17
Make up of your model

• 1 large trash bag to help with formation of your
  comet
• 1/3 Liter of water comets are made of mostly
  water
• 2/3 cup of dirt Sand and dirt take the place of
  interplanetary dust and silicates that
  are trapped in the frozen ice of comets.
  
• 1 teaspoon of corn starch helps hold the comet
  together
• 1 teaspoon of vinegar represents amino acids
• 1 teaspoon of alcohol represents methanol
• 1 teaspoon of corn syrup represents organics.
  Organic material means anything made up of
  four elements carbon, hydrogen, nitrogen,
  and oxygen
• 2 lbs of dry ice Comets are frozen gases

18
Making a model of a comet

• http//www.jpl.nasa.gov/education/videos/playVideo
  .cfm?videoID17
• http//www.youtube.com/watch?vtYc25Jt5RSk
• http//cse.ssl.berkeley.edu/SegwayEd/lessons/comet
  stale/frame_game.html

19
Test Your Knowledge

• What is the lifespan of a comet?

• 10,000 years or 1,000 revolutions

20
Test Your Knowledge

• What is the cloud of diffuse material surrounding
  a comet called?

• A coma

21
Test Your Knowledge

• What is the average number of comets that can be
  seen by the naked eye every year?

• One a year

22
Test Your Knowledge

• Why do you think that your model is a good
  representation of a comet?

23
Test your knowledge

• Why do astronomers use models?

24
Test Your Knowledge

• What is one name for a comet that is far away
  from the sun and has a nucleus that is in a
  frozen solid state?

• "dirty snowball"

25
Turn in

• Make sure you turn in your homework, lab sheet
  and your constellation project. You may turn in
  constellation projects next class as well.
• Please make sure that your table is cleaned up,
  wiped down and all materials are returned to the
  roll cart. Comets should be in the orange basket
  in the sinks to sublimate.

26
(No Transcript)