[meteorite-list] Comet May Have Missed Earth By A Few HundredKilometres in 1883?

From: John Lutzon <jl_at_meteoritecentral.com>
Date: Mon, 17 Oct 2011 20:42:54 -0400
Message-ID: <BA619D95EBDB42F3A9BAA275D9AECD40_at_Home>

Hi Ron,

Thank you again for all of your posts---very informative.

I just gave up drinking beer and burned my will---no need for such trivia at
this point.

Does anyone have any data on this "Pons-Brooks" and/or are there any calcs.
on its possible return to our backyard?

Well, maybe one more beer while i wait for the flash.

John.

----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Monday, October 17, 2011 7:23 PM
Subject: [meteorite-list] Comet May Have Missed Earth By A Few
HundredKilometres in 1883?


>
> http://www.technologyreview.com/blog/arxiv/27264/
>
> Billion Tonne Comet May Have Missed Earth By A Few Hundred
> Kilometres in 1883
>
> Technology Review
> October 17, 2011
>
> A re-analysis of historical observations suggest Earth narrowly avoided
> an extinction event just over a hundred years ago
>
> On 12th and 13th August 1883, an astronomer at a small observatory in
> Zacatecas in Mexico made an extraordinary observation. Jos?? Bonilla
> counted some 450 objects, each surrounded by a kind of mist, passing
> across the face of the Sun.
>
> Bonilla published his account of this event in a French journal called
> L'Astronomie in 1886. Unable to account for the phenomenon, the editor
> of the journal suggested, rather incredulously, that it must have been
> caused by birds, insects or dust passing front of the Bonilla's
> telescope. (Since then, others have adopted Bonilla's observations as
> the first evidence of UFOs.)
>
> Today, Hector Manterola at the National Autonomous University of Mexico
> in Mexico City, and a couple of pals, give a different interpretation.
> They think that Bonilla must have been seeing fragments of a comet that
> had recently broken up. This explains the 'misty' appearance of the
> pieces and why they were so close together.
>
> But there's much more that Manterola and co have deduced. They point out
> that nobody else on the planet seems to have seen this comet passing in
> front of the Sun, even though the nearest observatories in those days
> were just a few hundred kilometres away.
>
> That can be explained using parallax. If the fragments were close to
> Earth, parallax would have ensured that they would not have been in line
> with the Sun even for observers nearby. And since Mexico is at the same
> latitude as the Sahara, northern India and south-east Asia, it's not
> hard to imagine that nobody else was looking.
>
> Manterola and pals have used this to place limits on how close the
> fragments must have been: between 600 km and 8000 km of Earth. That's
> just a hair's breadth.
>
> What's more, Manterola and co estimate that these objects must have
> ranged in size from 50 to 800 metres across and that the parent comet
> must originally have tipped the scales at a billion tonnes or more,
> that's huge, approaching the size of Halley's comet.
>
> That's an eye opening re-examination of the data. Astronomers have seen
> a number of other comets fragment. The image above shows the
> Schwassmann-Wachmann 3 comet which broke apart as it re-entered the
> inner Solar System in 2006. There's no reason why such fragments
> couldn't pass close by Earth.
>
> One puzzle is why nobody else saw this comet. It must have been
> particularly dull to have escaped observation before and after its close
> approach. However, Manterola and co suggest that it may have been a
> comet called Pons-Brooks seen that same year by American astronomers.
>
> Manterola and co end their paper by spelling out just how close Earth
> may have come to catastrophe that day. They point out that Bonilla
> observed these objects for about three and a half hours over two days.
> This implies an average of 131 objects per hour and a total of 3275
> objects in the time between observations.
>
> Each fragment was at least as big as the one thought to have hit
> Tunguska. Manterola and co end with this: "So if they had collided with
> Earth we would have had 3275 Tunguska events in two days, probably an
> extinction event."
>
> A sobering thought.
>
> Ref: arxiv.org/abs/1110.2798 <http://arxiv.org/abs/1110.2798>:
> Interpretation Of The Observations Made In 1883 In Zacatecas (Mexico): A
> Fragmented Comet That Nearly Hits The Earth
>
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Received on Mon 17 Oct 2011 08:42:54 PM PDT