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THE IMPACT OF COMETS AND ASTEROIDS UPON THE EARTH


By Donald K. Yeomans
Supervisor, Solar System Dynamics Group
Jet Propulsion Laboratory
Monday, May 17, 1999
7:30 p.m. at
GRIFFITH OBSERVATORY

Comets and asteroids have been receiving bad press of late. In two recent movies, they have been portrayed as Earth threatening villains. While comets and asteroids do smack into the Earth from time to time, it is also likely that they helped deliver the water and carbon-based molecules to the early Earth, thus providing the building blocks for the formation of life. Subsequent collisions may have punctuated life's evolutionary cycles allowing only the most adaptable species to evolve further. We mammals may owe our preeminent position atop the Earth's food chain to a collision some 65 million years ago that wiped out most of our competition - including the dinosaurs.

Ironically, the same comets and asteroids that can most closely approach the Earth are also the most accessible in terms of exploiting their vast supplies of water and metals. Comets and asteroids could easily supply the raw materials necessary for colonizing the inner solar system in the next century. In addition to the utility of assessing their potential as future threats and resources, there are compelling scientific reasons for studying these primitive leftovers from the solar system formation process. Knowledge of their compositions and structures will provide important clues to the conditions and chemical mix from which the planets formed some 4.6 billion years ago. The nature and chemical composition of these enigmatic objects should soon become clear as spacecraft missions closely study a dozen comets and asteroids in the next 13 years.

At the Jet Propulsion Laboratory, Don Yeomans is a Senior Research Scientist and Supervisor for the Solar System Dynamics Group. Dr. Yeomans is the Project Scientist for the MUSES-CN mission to explore the surface of a near-Earth asteroid and Radio Science Team Chief for the Near-Earth Asteroid Rendezvous (NEAR) mission. He is the current Chairman for the Division of Planetary Sciences and has recently been appointed manager of NASA's Near-Earth Object Program Office. His research work is focused upon the physical and dynamical modeling of comets and asteroids. He has been active in providing the observing community and flight projects with position predictions for hundreds of comets and asteroids including those that have been, or will be, mission targets. In refining the motions of comets and asteroids, he has used data types as diverse as recent radar measurements, Hipparcos-based astrometry, and ancient Chinese observations. Don has received 10 NASA Achievement awards including an Exceptional Service Medal in 1986. He has published three books and over 100 technical papers. Asteroid 2956 was renamed 2956 YEOMANS to honor his professional achievements.

Friends Of The Observatory (FOTO) is the non-profit support group for Griffith Observatory. Currently, one of FOTO's primary goals is to support the renovation and expansion of the Observatory, so that it continues to provide the nearly 2 million visitors and 50,000 school children annually with accurate astronomical and scientific information and programs and remains the internationally recognizable icon of Los Angeles.

Admission: $2 for FOTO members, $5 for non-members; tickets are available at the door. (Children under 5 are not admitted.)

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