[meteorite-list] What killed off megafauna?

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Fri, 24 Jun 2016 03:05:04 -0400
Message-ID: <1558139ec1e-5fbc-b8f9_at_webprd-m62.mail.aol.com>

The following scenario estimates error in protection referencing Earth's atmosphere rather than gravity alone. It assumes Earth's atmosphere extends 100 km into space and treats everything as spherical or spherical shells. If all impactors crossing through the atmosphere are assumed sucked into Earth (an exaggeration, but a way to get a handle for the error) due to the deceleration they experience, the protection Earth with its atmosphere offers the Moon is less than 10% additional than if there were no Earthly atmosphere. Gravity itself is even less of an effect. Think about the example the Grand Teton fireball of 1972 passed through the atmosphere at a close approach of only 57 km above ground level but did not impact Earth. The concept is to focus on the relative cosmic velocities involved - impactors are generally totally different animals going on their ways, compared to satellites placed in precision Earth centered orbits (net vector of relative velocity to Earth is zero) which decay into falling
junk.

We can assume Earth will change the trajectories of potential impactors, but there will be no favoring of diverting vs. sending onward to Lunar collision trend.

The one exception is that the Earth indeed can protect the Moon against these quasi Moon type NEOs by establishing a safe zone, but only one quasimoon vs. the rest of the objects in the neighborhood is an extremely minute fraction, or effectively maybe zero at times, of potential impactors.

The numbers:,

Earth-Moon distance = 384,400 km

Earth Radius = 6,371 km
Earth plus atmosphere Radius = 6,571 km
Atmosphere defined with height = 100 km)

Area of Lunar spherical celestial shell at E-M distance
1.853 X 10^12 km2

Cross Sectional Area of solid Earth
1.275 X 10^8 km2
Cross Sectional Area of Earth with atmosphere
1.356 X 10^8 km2

ratio to solid Earth
1/14,500
ratio to Earth with atmosphere
1/13,700


Best wishes
Doug


-----Original Message-----
From: Matson, Rob D. via Meteorite-list <meteorite-list at meteoritecentral.com>
To: E.P. Grondine <epgrondine at yahoo.com>; meteorite-list <meteorite-list at meteoritecentral.com>
Sent: Thu, Jun 23, 2016 10:03 pm
Subject: Re: [meteorite-list] What killed off megafauna?

Earth provides no real protection for the Moon from asteroid/meteoroid impact. I think the earth subtends something like one 15,000th of the celestial sphere from Luna's perspective. Yes, there is a gravitational factor that improves that a bit, but you're still talking a tiny fraction of a percent "protection". Doubt it's even measurable as far as earth impact rate vs. Moon's. --Rob
________________________________________
From: Meteorite-list [meteorite-list-bounces at meteoritecentral.com] on behalf of E.P. Grondine via Meteorite-list [meteorite-list at meteoritecentral.com]
Sent: Thursday, June 23, 2016 4:39 PM
To: meteorite-list at meteoritecentral.com
Subject: [meteorite-list] What killed off megafauna?

Hi Paul -

Two of the impact events are now pretty well known:

http://archaeologica.boardbot.com/viewtopic.php?f=9&t=3656
http://archaeologica.boardbot.com/viewtopic.php?f=9&t=3668

Of course, work is just beginning on the sequence of impacts for South America and their
related meltwater pulses.

It is really strange to watch the psychological process of denial going on here.
I wish I had just a small part of the money spent on this denial for more research into what actually occurred.

Or better yet, have your personal salary dependent on actual impact research.
That would certainly focus your own fine skills.

BTW, you can not use impact data from the Moon in a straight line to estimate the
impact hazard for the Earth.

The Earth usually protects the Moon from impactors.

E.P.
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Received on Fri 24 Jun 2016 03:05:04 AM PDT