[meteorite-list] What killed off megafauna?

From: MexicoDoug <mexicodoug_at_meteoritecentral.com>
Date: Sun, 26 Jun 2016 17:17:56 -0400
Message-ID: <1558e93744c-46ad-5ebc_at_webprd-m11.mail.aol.com>

Hi Ed and thanks for spirited discussion,

I already covered most of what's wrong with your caricature of the Earth-Moon system when I discussed cosmic velocities in my original post. In science terms, the kinetic energy swamps the Earth's gravitational potential you are relying upon to protect the Moon from impact.

Unfortunately the media continue to characterize the Earth and Moon as if they were these massive objects a whisper apart. It is as bad a caricature as it gets. Your first link to the Cassini image is confusing you and not representative of the relatives sizes and distances of Earth's and the Moon's disks. You are looking a images of light closer to the limit of the resolution from Saturn, which for all I know as well were taken at that precise moment to capture a Moonrise ... when the moon emerges from being eclipsed, an aesthetic planetary imaging target. You are then saying this is what at impactor sees. Saturn is around a billion miles away! That I assure you is not what an impactor sees!

Your second video is a joke. Here is the video I ask you watch in reply to your bad geometry/astronomy lessons. as it pertains to impact shielding, and to give you a better visualization of how big space is and how insignificant our little planet is, even in the scheme of the Moon. Try to imagine how few objects approach the Moon after grazing Earth, or how few would reach it if not impacting Earth:

https://www.youtube.com/watch?v=Bz9D6xba9Og

As far as adjusting our models, lol, that would be Newton's department, not mine, though Rob might enjoy tweaking Newton ;-). The apple reputedly impacted his head and was not sucked into the trunk of the of the massive apple tree that had him daydreaming. Had it been otherwise, Newton's law of gravity might have been different and the gravitational constant might have allowed the Earth to protect the Moon from impacts with some practical significance. You do not provide a reference for your claim about significant impact protection of the Moon by Earth I won't reply on that one. It requires digging through your notions of why Rob and I may have defective understandings. There may be some interesting discussion there as to your notions and interpretations, but the other references you gave don't convince me to be a grunt at the moment ;-)

Back to the concept of cosmic velocity (and the related law of conservation of momentum). If you take Newton's law of gravity between Earth and a would-be impactor coming in, and set it equal to the kinetic energy at the top of Earth's atmosphere it would need to be captured, you will see that the velocity relative to Earth must be less than 11.1 km/sec. That is an awfully slow moving rock. That speed is known as an escape velocity. Notice I said at the top of our atmosphere (100 km high). The speed drops off. Geosynchronous satellites have an escape velocity of just 4.3 km/sec. Cosmic velocities can well over 10 times that. The orbits can be bent, but unless they are on a very precise path to impact long before entering the Earth Moon system, they simply would fly right on by if they are moving faster than this velocity but not already headed for impact. As a matter of fact, beyond a geosynchronous orbit, I believe the Sun's gravitational pull is greater than Earth's. That's a cool fact to know, co
nsidering Earth and the Moon are still pockmarked regularly.

This is the hard part of space exploration. Impact or orbital insertion can be much more precision maneuvers than uncontrolled flybys. If you think differently, I recommend taking up golf, maybe putting is easier than they say!

Kindest wishes
Doug



-----Original Message-----
From: E.P. Grondine via Meteorite-list <meteorite-list at meteoritecentral.com>
To: meteorite-list <meteorite-list at meteoritecentral.com>
Sent: Sun, Jun 26, 2016 12:11 pm
Subject: [meteorite-list] What killed off megafauna?

Hi Rob, Doug -

(Glad to hear that you're doing okay, Doug)

What both of you need to do is to take the perspective of a potential impactor passing through the inner solar system,
as seen in the first few seconds of this video:
https://www.youtube.com/watch?v=GDrBIKOR01c

The basic geometry of the problem is set out here:
https://www.youtube.com/watch?v=qTDcfI2dabk

If it makes it easier,
think of the Earth-Moon system as a pair of girls at a darkly lit party,
and yourself as a young man.
(A variant of the famous mathematical problem of the drunk's walk at the frat party.)
While you may be attracted to the "prettier" (in terms of gravity/area) Moon,
you are far more likely to run into her much larger "wingman", the Earth.
Sorry, but that is just the way it is.

At first, you're getting a warm fuzzy feeling (gravity) from the combined Earth/Moon system.
That warm fuzzy feeling varies by the cubes of the radius of each of the two bodies,
and is located somewhere amongst them.

On your approach to the Earth/Moon system, you see your landing area (for only part of the month, see second video)
in terms of area, which varies by the square of the radius.
But of course gravity also varies by distance,
so as you get close to theses two
you're getting far more of that warm fuzzy feeling from the Earth,rather than the Moon.
You head that way.

You can use any computer language you prefer to model this system,
and run it on any machine you like.
But as a check on your computer model, you have to rely on the data.
In this case, compare the data on smaller impactors from the Moon,
(Apollo seismic and optical astronomy)
with the data from the reconnaissance systems which have been operating
on the Earth since the 1950's,
and "alarming" the "stuff" out of those looking at the data from them.

If there is a difference between your model's results and the data, then your model is defective.
 
(An entertaining video on phonetic loading,
the diameters of lunar craters,
typing monkeys, and other natural phenomena:
https://www.youtube.com/watch?v=fCn8zs912OE)

good hunting,
E.P.

PS - Will NEOcam make meteorite hunting far easier?
Will the increased supply drive down prices even further?

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Received on Sun 26 Jun 2016 05:17:56 PM PDT