Every couple of years, the earth is hit by a body with energy near that of the Hiroshima bomb. Deposited high in the atmosphere these events causes little or no damage. On longer timescales, impacts occur with the potential to destroy regions, or whole civilizations. This lecture presents an overview of the impact threat, followed by a systematic development of the requirements to divert such an object. Nuclear explosives are presented as a mature, well-characterized technology able to reduce or eliminate this threat. With decades of warning, a standoff burst can then ablate surface material and nudge the body to a safer orbit without fragmenting. For shorter times, 1000 days before impact, a direct surface burst can shatter the body dispersing the material so much that only about 1/100,000th of the original body, still threatens.

Speaker Bios

Dr. David Dearborn

Dr. David S. P. Dearborn is a graduate of UCLA (1970) and the University of Texas at Austin (1975). He has held positions at the Copernicus Institute in Warsaw, the Institute of Astronomy in Cambridge, The California Institute of Technology, and Steward Observatory in Tucson. He is currently a research physicist at the Lawrence Livermore National Laboratory.

He was the 1998 Shelby Fellow of the Australian Academy of Science, has received two Pollock awards for studies in the History of astronomy, and three "Weapons Recognition of Excellence" awards from the Department of Energy. These awards recognized his contributions to laser hohlraum development, his work advancing the analysis of radar data, and finally for his efforts on the W87 Life Extension Program. In 2006, he received a DNT acknowledgement for "outstanding contributions of the cross discipline improvement of ICBM accuracy ...", and others (in 2007 and 2008) for "warhead contributions in support of Prompt Global Strike."

His astrophysical research includes publications on observations of isotope ratios in red giants, as well as the discovery of several short period variables. However, most of his astrophysics work involves theoretical studies on the physics of stars, including stellar nucleosynthesis, and astro-particle physics. He is currently involved in Djehuty, a project for the full three-dimensional modeling stars, which recently led to the discovery of a new mixing mechanism that resolves a decades old conflict between predicted and observed abundances.

His work on the astronomy of the Inca includes the discovery of a set of Inca pillars marking the June solar position at the Island of the Sun in Bolivia. This and other Andean work has resulted in a dozen journal publications and a book on the subject. He is a full member of the Institute for Andean Studies, a founding member of the International Society for Archaeoastronomy, and Astronomy in Culture (ISAAC), and until recently was one of four principal editors for the journal Archaeoastronomy, published by the University of Texas Press.

His programmatic work has included the design and testing of both nuclear and conventional explosives. Current responsibilities include generating models and output for the DTRA Red Book, support of the LLNL RV flight-test program, and conventional lethality studies. He has used large lasers for the study of high energy density phenomena, studied non-seismic methods for treaty verification, and designed a shuttle experiment.

His current research on the diversion of asteroids by nuclear explosives mixes his skills in astrophysics and nuclear weapons effects. It began in 2003 for the Planetary Defense Conference, and resulted in publications cited by NASA's 2006 Near-Earth Object Survey and Deflection Study for the congress. Today, this research continues with detailed modeling of the effects of nuclear explosives on asteroids.

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.