For eons, humans have gazed up at the night sky, and sailors even set their course by the regular motions of the sun, moon and stars. The occasional appearance of comets, new bright objects with glowing tails, in the regular patterns of the night sky has awed humans throughout history. Today, we know comets formed in the frozen outer reaches of the solar system and were thrown into orbits that bring them near the sun where they develop tails of gas, dust and ions. ...but how much do we really know about comets? ...did a comet kill the dinosaurs?... and what can comets tell us about our own ancient history?

NASA's Stardust mission traveled to a comet, flew through its tail and returned to Earth last year with real comet dust for researchers to study. Now, astronomers, physicists, chemists, materials scientists and computer scientists are doing some detective work. In this lecture, we will look at how comets formed, their role in the Earth's history and the clues we are finding about what happened over 4 billion years ago.

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Today you will learn

  • Why have comets historically been feared?
  • What are comets made of?
  • What is the nature of comet tails?
  • Where are comets found in the Solar System?
  • How can you make a "comet" in a classroom?
  • Why do we study comets?
  • How did the Stardust probe collect samples from the comet Wild-2, and return those samples to the Earth?
  • What surprising insights about our Solar System have we learned by studying the Wild-2 comet samples?


Students will learn about the nature of comets and how scientists at LLNL are studying comet samples returned to Earth by the Stardust mission, and how these tiny samples of space dust may hold the key to understanding the formation of our own Solar System.

Student Lecture Notes

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1. What are the "normal" objects one might expect to see in the sky on a clear night?


2. How are comets different from these "normal" objects?


3. List in order, from largest object to smallest: A comet nucleus, Earth, Pluto, Earth's Moon, Charon (Pluto's moon).


4. Which of the following is NOT part of a comet's composition? (More than one may be correct.)

a. Water ice
b. Frozen carbon dioxide
c. Minerals (rocks and dust)
d. An iron/nickel core
e. Organic (carbon-based) compounds
f. Nougat and caramel

5. What are the two tails of a comet made of?


6. In which direction does a comet's tails point?

a. The direction the comet is going.
b. The direction the comet is coming from.
c. Away from the Sun.
d. Toward the Sun.
e. Toward Albuquerque, New Mexico


7. True or False: The planets of our Solar System, and everything on them - including us - were formed from stardust ejected from other stars in our Galaxy.


8. How long ago did our Solar System form?


9. In the early Solar Nebula, what did bodies closer to our Sun than the "frost line" tend to be made of? What about objects farther than the "frost line?"


10. True or False: Comets act like frozen time capsules, containing material preserved since the Solar System formed.


11. True or False: There is no possible connection between the beginning of life on Earth and comet bombardment.


12. How far did the Stardust spacecraft travel from the Earth?

a. A thousand miles.
b. A million miles.
c. 1 A.U.
d. 2.72 A.U.
e. 2.72 light years.


13. When was comet Wild-2 deflected from a larger orbit into one that takes it into the inner part of the Solar System?

a. 4.6 billion years ago.
b. 65 million years ago.
c. 60,000 years ago.
d. 3,000 years ago.
e. 1974.


14. What type of ultra-low-density material was used by Stardust to capture comet dust?


15. Which is wider: a human hair or a typical comet sample returned by Stardust?


16. True or false: LLNL scientists have found rocky material in the Stardust samples that seems to have been heated by the Sun at some point, implying the material used to be close to the Sun, and then was churned into the outer part of the Solar System long ago.

Speaker Bios

Dr. Hope Ishii

Research Scientist, Institute for Geophysics and Planetary Physics
Lawrence Livermore National Laboratory

Hope earned her Bachelor’s degree in Materials Science and Engineering from Cornell University and her Ph.D. at Stanford University. In between, she traveled to Sweden for her Master’s degree in Physics and Engineering Physics. She has studied a wide range of materials from nanocomposites to liquid crystals to glass and specializes in synchrotron x-ray studies. Since 2003, Hope has been at Lawrence Livermore National Laboratory studying extraterrestrial samples and the stories these materials tell about our solar system. Most recently, she has been studying comet dust from NASA’s Stardust mission.

Tom Shefler

Granada High School

Mr. Shefler received a Bachelor of Science degree in physics and applied mathematics from Western Michigan University in 1997 and a Master of Arts degree in astronomy and astrophysics from the University of California at Berkeley in 2000. While at Berkeley, he researched analyzed and cataloged Hubble Space Telescope images of galaxies, observational research involved in the detection and study of extrasolar planets, and discovered Supernova 1998DT while working with the Katzman Automatic Imaging Telescope team. During his graduate studies he fell in love with teaching and entered the teaching profession in 2002.