First International Conference on MOLDAVIAN RISKS – FROM ...

<strong>First</strong> <strong>International</strong> <strong>Conference</strong> on MOLDAVIAN RISKS - FROM GLOBAL TO LOCAL SCALE
16-19 May 2012, Bacau, Romania
THE HAZARD OF IMPACTS FROM SPACE
Michael Purucker
Planetary Geodynamics Laboratory, GSFC/NASA, Greenbelt, MD USA
Corresponding author: Michael Purucker, Michael.E.Purucker@nasa.gov
Abstract: Near-earth objects (NEOs) have been implicated in mass extinctions in Earth
history. The most recent mass extinction occurred at the End-Cretaceous, and is associated
with the Chixulub impact structure in Mexico and the Deccan traps in India. NEOs
comprise both the much more abundant asteroid component, with orbits between 0.98 and
1.3 astronomical units, and the much rarer cometary component. NASA has now cataloged
90% of NEOs larger than 1 km (civilization ending) and has begun the task of identifying
those larger than 140 m (city killers). NEOs are identified by earth-based telescope, but an
infra-red space-based telescope in an orbit between the Earth and Venus would offer
superior viewing geometry for these dim objects. NEOs have no substantial gravity well,
and hence are ideal targets for both NASA’s robotic and human exploration program. The
natural history of NEOs suggests that they originate via planetary resonances from the
main asteroid belt and the trans-Neptunian disk, and that their dynamical lifetimes are on
the order of 10 Myr. Once identified, their threat can be assessed via precise orbit
determination, and steps might be considered to re-direct them away from Earth. However,
the complex interaction of science, psychology, politics, and money has hindered attempts
at an integrated global approach to the problem. The threat from NEOs was much more
common in the deep past, in what is termed the Late heavy bombardment 4 billion years
ago. This is a period when most of the Moon’s largest impact basins were formed, and by
inference the largest impact basins on Mercury and Mars.
Key words: impacts, hazard, extinction, planetary defense.
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