[FPSPACE] The NASA line on impacts: understating the hazard by an order of magnitude

[E.P. Grondine]

http://www.space.com/scienceastronomy/090728-asteroid-threat.html

I want to thank David for reminding everyone at fpspace that I am the only person here who has researched this subject in depth.

In Yeoman's interview, you'll note the confusion between NEOs, which includes both NEAs (Near Earth Asteroids) and NECs (Near Earth Comets), and that the impact hazard figures for both are not broken out.

This is NOT a trivial matter, but rather is directly tracible to Dr. Morrison and Dr Muller's very early and FAULTY work on cometary injection mechanisms. As Dr. Morrison controlled NASA research funding. the result has been an institutional bias within NASA, which Yeoman's statements reflect.

Note carefully his failure to mention Comet Schwassmann Wachmann 3, which is headed our way in 2022, or even the climate hazard presented by SW3's dust veil. 

In fact, COMETS, and not asteroids, account for the bulk of the impact hazard. And comets and their fragments present very difficult detection challenges.

Most of the ELEs are tracible to cometary impact, not asteroid impact, and occur at roughly 26 million year intervals. The rate of cometary injection is not uniform, and where we are in the cycle is unclear.

As far as 60 meter comet fragments go, they appear to have been hitting recently at a rate of 1 per 100 years. Larger land impacts have been occurring at at rate of roughly 1 per 3,000 years, with ocean hits and resulting megatsunami at a rate of 1 per 1,000 years.

While there appear to have been large iron impacts in the US (Barringer crater, 44,000 BCE or so), Alaska (32,500 BCE or so) and Siberia (27,000 BCE or so), for the Americas in recent times there have only been minor  asteroid hits at Campo de Cielo (2,360 BCE) and Brenhem (ca 100 CE). 

As far as the impact hazard goes, it is possible that most of the NEAs have already accreted, and asteroids travel at lower velocities than comets and their fragments. 


On the other hand, the effects of cometary impacts and comet dust veils have been catastrophic.

I suspect that it will only be once the first Infra-red NEO telescope is placed in orbit that the extent of the cometary impact hazard will be fully understood. 

E.P. Grondine
Man and Impact in the Americas
(still waiting for the cores from the Carolinas)

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