David Morrison's NEO News memo from November 2006

A CHALLENGE TO THE SCIENTIFIC CONSENSUS ON NEO IMPACT RISK

David Morrison [dmorrison@arc.nasa.gov]

NEO News

November 14, 2006

Minority View on Impact Frequency

This edition of NEO News contains two items; (1) A brief update on the NASA NEO study in response to the Congressional request for a plan to discover, track, catalog, and characterize sub-km NEAs and to consider technologies for mitigation; (2) A New York Times story about a multidisciplinary group of mostly geoscientists who are finding evidence suggesting that Earth has been subject to very large recent impacts and mega-tsunamis. I am sorry that there has been such a long time since the last edition of NEO News.

In June we reported on the NASA NEO Workshop held in Vail to collect information on NEO surveys, characterization, and mitigation as background for the reply to Congress, which Mike Griffin will give next month. Recall that Congress changed the basic NASA authorizing legislation to give the agency increased responsibility for understanding NEOs and eventually protecting against the impact threat. Since June a NASA team has been working on these issues. They have developed a draft recommendation of more than 100 pages called "2006 Near-Earth Object Survey and Deflection Study". A preview of their conclusions was recently briefed to the NASA Administrator, senior executives, and Center Directors, with request for their comments. Presumably this process will lead shortly to a final recommendation to the Administrator, and he in turn will make his recommendation to Congress sometime in December. As I understand it, the draft report concentrates on the survey and future mitigation studies, and is relatively light on NEO characterization.

I do not know if either the current draft report or its final version will be released. I do presume, however, that the formal NASA response to Congress will be a public document, available in a month or so.

On the second topic, the NY Times article (below) reports on an international group of scientists who dispute the standard understanding of impact frequencies. They quote both early written documents and geological evidence to suggest a much higher impact rate during the Holocene (the past 10,000 years). As noted in this article, the most recent assertions involve evidence for mega-tsunamis within this period, on a scale that suggest one or more impacts in the 100,000 megaton range. Previously there have also been claims for smaller Tunguska-class impacts occurring at a rate of several per century. These impact rates are at least an order of magnitude greater than is calculated from the current population of NEOs. As I am quoted in this article, if they are right and they find convincing evidence for multiple recent tsunamis, we'll have a real contradiction on our hands.

David Morrison
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David Morrison, NASA Ames Research Center 240-1
Tel 650 604 5094; Fax 650 604 4251; Cell 650 278 0343
david.morrison@nasa.gov or dmorrison@arc.nasa.gov
website: http://nai.arc.nasa.gov
website: http://impact.arc.nasa.gov