[meteorite-list] Comet smashes triggered ancient famine ???

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Sun, 11 Jan 2009 05:54:41 -0700 (MST)
Message-ID: <51695.71.226.60.25.1231678481.squirrel_at_timber.lpl.arizona.edu>

Hi Graham and Rob:

Some of this is from memory and some of this I had to look up. David Levy
was actually working part time for me at the time doing education
outreach, so I know some of the details.

1. As far as I know, scientists still do not know where SL9 came from
("beyond Neptune"). Probably a captured comet that happened to come too
close to Jupiter on its first pass or one of its first passes into the
inner part of the Solar System.

2. At some point in time (1960s to 1970s), the comet(?) soon to be called
SL9 was captured in a 2-year orbit around Jupiter. Good for it, a new moon
of Jupiter!

3. However in July of 1992, SL9 passed within 30,000 to 40,000 km of
Jupiter's cloud tops (Jupiter radius is about 71,500 km). This is within
the Roche limit of Jupiter (gravity-induced tides from Jupiter stronger
than the strength of the material that makes up the body; a little more
complicated than that, but good enough for this).

4. Observed first seen by Carolyn Shoemaker (observers Gene and Carolyn
Shoemaker and David Levy; interesting story). Then confirmed by Jim Scotty
here in Arizona (the first famous image of the string of pearls).

5. Soon determined to be in orbit around Jupiter (though only "seen" once
prior to that but not noticed by the person who took the image). A highly
elliptical orbit that had it going as far as 50,000,000 km from Jupiter
(but still in orbit). Repeating myself, a 2-year orbit, probably in orbit
for 20 or 30 years.

6. Soon to be determined that its orbit was continually changing slightly
(gravity of the Sun and mass loss of the comet which alters the orbit
slightly). The result was that in Juuly of 2004, it would be at its
closest to Jupiter again, but this time, its closest distance to Jupiter
would be 45,000 from the center of Jupiter, 26,500 BELOW the cloud tops of
Jupiter!

7. So, the reason that all of the pieces hit Jupiter was that they were
all in the same orbit, just strung out in space (and time along an orbit
that got the pieces way too close to Jupiter).

8. I think that the best estimates (not all agree) are that the largest
pieces were at most 1-2 km in diameter with most pieces less that 1 km in
diameter. This makes this event a once in a thousand-year event (give or
take).

9. This helps explain crater chains on two of Jupiter's satellites: Europa
and Ganymede (16 total?). A comet gets too close to Jupiter, breaks up and
you get a string of comets that, on their way away from Jupiter run into
one of the satellites, leaving a crater chain. Too close together and
there would not be a chain. Too far apart and only one or two would hit
the satellite and the others would miss.

To get crater chains on Earth, you would have to have a comet or asteroid
break up before hitting the Earth, either by a close approach to Earth
(unlikely) of the Sun. However, it is unlikely that this object would get
captured by the Earth (they are moving fast and Earth not that massive).

A breakup as the object was approaching the Earth (say in the atmosphere)
would not give the pieces time enough to spread out and make multiple
craters (the long discussion on double craters on Earth). So the pieces,
as I said before, would have to be close enough together in order for the
individual pieces to hit the moving Earth target and really close to make
a chain on Earth. The Earth is moving at 30 km/s and a comet is moving at
probably 40 or 45 km/s. So, you can easily figure out how close the pieces
have to be.

A bunch of impacts over a few thousand years is another story that is
beyond the above discussion.

Larry






On Sun, January 11, 2009 2:49 am, ensoramanda at ntlworld.com wrote:
> Hi Rob,
>
>
> Went to a lecture at our astronomy society about Jupiter and it acting to
> capture or perturb objects (friend or foe etc) the other night.... and I
> believe it was said that SL9 only made two passes before it met jupiter
> again on jupiters next turn around the sun and was thus flung out never
> to be seen again. eg Jupiter was on the opposite side of the sun on SL9's
> first time round with no effect and thus was very close 2nd time round
> and able to change its orbit again.
>
> I hope I remembered that right!
>
>
> Graham Ensor, UK
>
>
>
> ---- Rob McCafferty <rob_mccafferty at yahoo.com> wrote:
>
>> Fair point, but it may well be a poor choice of words on my point.
>>
>
> The "Swarms"/"showers" you mention are what are suggested in the book.
> Several objects arriving in quick sucession are not unusual, however.
> There is evidene of it happening on most solid bodies. They all have
> strings of impact craters where many objects obviously arrived in a
> matter of hours producing chains of craters. My problem with this is that
> the authour is perhaps suggesting several over the last few millenia. If
> the "chain" events were that prevalant, one would expect them to dominate
> on solid bodies and they don't.
>
> Your points are well made. I was not aware that SL9 was in orbit of
> Jupiter. The implications of this are complex and I'll need to check how
> long for. I Doubt it was for long but even so, how this is related to
> comets and the earth is beyond me at this time.
>
> Rob
>
>
>
> --- On Sat, 1/10/09, lebofsky at lpl.arizona.edu <lebofsky at lpl.arizona.edu>
> wrote:
>
>
>> From: lebofsky at lpl.arizona.edu <lebofsky at lpl.arizona.edu>
>> Subject: Re: [meteorite-list] Comet smashes triggered ancient famine ???
>> To: rob_mccafferty at yahoo.com
>> Cc: "tracy latimer" <daistiho at hotmail.com>,
>> meteorite-list at meteoritecentral.com Date: Saturday, January 10, 2009,
>> 11:47 PM
>> While I have not read this book, generally, comets cannot
>> hit the Earth over a short interval like SL9. SL9 was in orbit around
>> Jupiter. It is
>> highly unlikely that a comet could be captured in orbit around Earth.
>> Continuous bombardment on Earth only happens in movies
>> unless there is a massive swarm of objects (like in a meteor shower).
>>
>> The Earth is a moving target, so if one comet piece were to
>> hit the Earth, it is unlikely that a second or third one in a similar
>> orbit would hit, unless the cluster was VERY bunched together. The Earth
>> would be long gone!
>>
>> The Earth's orbital velocity is about 30 km/s and its
>> diameter is about 12,750 km. So the Earth moves its diameter in about 425
>> seconds. If the comet pieces were farther apart than that, only one
>> piece would hit.
>>
>> Larry
>>
>>
>> On Sat, January 10, 2009 4:06 pm, Rob McCafferty wrote:
>>
>>> This is not a new idea. Mike Baille's book
>>>
>> "Exodus to Arthur" makes
>>
>>> interesting reading on the idea that comets may have
>> triggered many human
>>> catastrophies in the past. His book is based on
>> dendochronology with
>>> support from other sources. At the time of publishing
>> c.2000, there was a
>>> gap in the Greenland Ice core during the 6th Century.
>>>
>>> The first third of the book is compelling reading but
>>>
>> for me does little
>>> to convince me that it was anything other than
>> volcanic eruptions. The
>>> latter part of the book is based on written accounts,
>> myths and legends
>>> to make a the suggestion that clusters of small comets
>> may have been
>>> involved, small fragments arriving in short interval
>> like SL9 did on
>>> Jupiter in 1994.
>>> He's as objective as he can be but is clearly
>>>
>> convinced of the cometary
>>> contribution in at least a few cases.
>>>
>>> Rob McC
>>>
>>>
>>>
>>>
>>> --- On Fri, 1/9/09, tracy latimer
>>>
>> <daistiho at hotmail.com> wrote:
>>
>>>
>>>
>>>> From: tracy latimer <daistiho at hotmail.com>
>>>> Subject: Re: [meteorite-list] Comet smashes
>>>>
>> triggered ancient famine ???
>>>> To: "Paul" <bristolia at yahoo.com>,
>>>>
>> meteorite-list at meteoritecentral.com
>>>> Date: Friday, January 9, 2009, 7:15 PM
>>>>
>>>>
>>>>> From what little research I did, I had
>>>>>
>> understood that a
>>>>>
>>>> substantial chunk of the sun-blotting fog was
>> actually 'vog', which
>>>> outgassed from major eruptions in Iceland.
>> Iceland underwent several
>>
>>>> periods of volcanic activity during the 'Dark
>> Ages', where multiple
>>
>>>> volcanic vents burped out stifling clouds of gas.
>> The gas periodically
>>
>>>> got so thick and noxious that it poisoned
>> vegetation, killed animals,
>>>> and sickened almost everyone else; there was at
>> least one major exodus
>>>> of survivors around 770 a.c.e.
>>>>
>>>> Tracy Latimer
>>>>
>>>>
>>>>
>>>> ----------------------------------------
>>>>
>>>>
>>>>> Date: Fri, 9 Jan 2009 07:12:59 -0800
>>>>> From: bristolia at yahoo.com
>>>>> To: meteorite-list at meteoritecentral.com
>>>>> Subject: [meteorite-list] Comet smashes
>>>>>
>> triggered
>>>>>
>>>> ancient famine ???
>>>>>
>>>>> Comet smashes triggered ancient famine
>>>>> January 7, 2009 by Ker Than
>>>>>
>>>>>
>>>>>
>>>>
>> http://www.newscientist.com/article/mg20126882.900-comet-smashes-trigge
>>
>>>>
>> red-ancient-famine.html?DCMP=OTC-rss&nsref=online-news
>>>>>
>>>>> Abbott, D. H., P. Biscaye, J. Cole-Dai, and D.
>>>>>
>> Breger,
>>
>>>>>
>>>> 2008,
>>>>
>>>>
>>>>> Magnetite and Silicate Spherules from the
>>>>>
>> GISP2 Core
>>
>>>>>
>>>> at the 536 A.D. Horizon
>>>>> American Geophysical Union, Fall Meeting 2008,
>>>>>
>>>>>
>>>> abstract #PP41B-1454
>>>>>
>>>>>
>>>>
>> http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&rang
>>
>>>>
>> e=1&directget=1&application=fm08&database=%2Fdata%2Fepubs%2Fwais%2Finde
>>
>>>>
>> xes%2Ffm08%2Ffm08&maxhits=200&=%22PP41B-1454%22
>>>>>
>>>>> and
>>>>>
>>>>>
>> http://adsabs.harvard.edu/abs/2008AGUFMPP41B1454A
>>
>>>>>
>>>>>
>>>>> Yours,
>>>>>
>>>>>
>>>>>
>>>>> Paul H.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ______________________________________________
>>>>> http://www.meteoritecentral.com
>>>>> Meteorite-list mailing list
>>>>> Meteorite-list at meteoritecentral.com
>>>>>
>>>>>
>>>>>
>>>>
>> http://six.pairlist.net/mailman/listinfo/meteorite-list
>>
>>>>
>> _________________________________________________________________
>>
>>>> Windows Live???????: Keep your life in sync.
>>>>
>>>>
>> http://windowslive.com/explore?ocid=TXT_TAGLM_WL_t1_allup_explore_01200
>> 9
>>
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>>>
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>
>
>
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Received on Sun 11 Jan 2009 07:54:41 AM PST