Re: Possible evidence for Stone Age (Clovis) Cosmic Catastrophe?

Apparently on date Wed, 02 Nov 2005 17:16:19 +1300, Eric Stevens
<eric.stevens@xxxxxxxxx> said:

>On Tue, 01 Nov 2005 23:51:37 GMT,
>nospam@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
>
>>Apparently on date Wed, 02 Nov 2005 08:51:30 +1300, Eric Stevens
>><eric.stevens@xxxxxxxxx> said:
>>
>>>On Tue, 01 Nov 2005 13:59:22 GMT,
>>>nospam@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote:
>>>
>>>>3,000,000 meters per second, as suggested by the report, is not going to gather
>>>>interstellar hydrogen by merit of its gravity. Whereas, the same chunk of iron
>>>>rolling slowly through the outer solar system on the slow, steady aphelion
>>>>stages does pick up the stuff that litters space there.
>>>>
>>>>And when it falls back to the sun and slingshots round it back to the cold
>>>>outer orbit, the heat from the sun does burn off the lighter stuff and make a
>>>>tail. That's a comet.
>>>>
>>>>Whoever is talking about "the earth being hit by comets" is wrong, but
>>>>journalists seem to make a practice of that when it comes to comets.
>>>>
>>>>
>>>As seen on TV http://seds.lpl.arizona.edu/sl9/sl9.html
>>>
>>>Why not earth too?
>>
>>Sure, comets *can* hit Earth.
>>
>>But the situation is that a particular comet will do it and it will be a very
>>rare event.
>
>It all depends on what you mean by 'rare'. There are respectable
>astromers who believe it has happened in historical times.

I reject their opinion then, as I shall show with numbers.

The earth orbits in a flat plane, roughly circular. The diameter of this circle
is 1.5e+11 meters and the circumference is therefore about 1e+12 meters.

The width of the earth, the target as it were, is about 1.2e+7 meters wide.

Therefore the chance of impact as a comet crosses the orbit is about 1e+5,
which is 100,000 to one against. Pitching generous figures for gravity bringing
a near miss in enough to hit, and allowing for the fact that it could hit on
the way in or out, brings that to 10,000 to one against at best.

This is a bit like someone in space firing a laser at the surface of the earth
in an attempt to hit the top of your head. If they can't see you and have to
aim at random, the chances are not very high.

But it is worse than that, the comet also has to cross the orbit of earth on
the flat plane it lies on. If the comet comes in above the plane at the
position of the orbit, it cannot hit the earth and will miss on the way out
again, due to being below the plane of the orbit.

This is a bit like someone firing the laser at some point on the equator, but
you don't have to be there, you can be north or south of the equator, in which
case you will never be hit.

So lets be *really* generous and give the chance of being on the flat plane of
earth's orbit, plus or minus about 1e+7 meters (basically only about 7,000
miles which is chickenfeed in a cosmic sense) as maybe only 100 to 1

That gives the chance of an earth-crossing comet striking the earth about once
in every 10,000 * 100 = 1,000,000 attempts.

Now, how many comets have you seen? I've seen Hale-Bopp, and if memory serves,
when I was a child there was one called Kohoutek, and later on, Halleys Comet
came round in about 1986 was it?

Comets are not everyday events, they're quite rare, I should guess about one
per year on average, at most.

That makes a comet impact, on very simplified figures, about once per million
years, or something of that ilk.

For comparison:
http://neo.jpl.nasa.gov/images/torino_scale.jpg

Note this includes rocks and similar rather than just comets, which are far
more rare then arbitrary objects.

>>The supernova boys are talking about various waves of debris that will
>>definitely hit earth and proposing an impactor that also hits, and I don't have
>>any objection to that except that it isn't inevitable.
>
>It's the formation of a comet in the (astronomically) immediate
>aftermath of a super-nova that puzzles me. I'm not arguing against the

They don't, and I could go so far as to say that comets physically cannot form
- in the sense that we mean here on earth - near an active supernova. Are you
fishing for a joke about a snowball in hell? ;)

>>The odd bit of high speed rock that also crops up and hits some provincial
>>planet is just a bit of extras. Yes, it might. And might not. And any
>>particular impactor might be something mundane like a random comet. The odds
>>are long and the key thing about the debris is that it contains heavy metals
>>that say "I came from a recent supernova - and nowhere else as astrophysics
>>sees this."
>>
>I suggest you follow up some of the leads in http://tinyurl.com/7u9pa
>if you want to know why I don't share your view on the likelihood of
>comet impacts.

No, I already know you support the un-accepted views of Napier and Clube and
therefore this is just a reference to their ideas. I already know I reject
their ideas on the basis of their maths that adds something one way, and then
adds it again another way, etc, to the point where I would need to see version
2.0 with all the errors fixed before I would bother reading it again.

At the end of the day, the dinosaurs were finished off by an impactor, and this
is not an annual event, or common in any worthwhile sense of the word.
.

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