Hi Larry,
In the likely model for precapture SL9 I cited, the perihelion of the
comet varies regularly to about 2.5 and 3 AU (in the link:
http://tinyurl.com/742lbr I provided, figure 2), which is well within
the asteroid belt and its main mass d-planet Ceres' aphelion of 3AU. I
was clear about calling it a short period comet with low inclination
which is just semantics for a Jupiter family comet as you would like to
correct me (but I would not agree, nor disagree or that matter due to
relevance).
There are a lot of semantics, for example, take the awesome asteroid
(944) Hidalgo, named for the Mexican Independence hero and preist.
Like it or not, it is generally considered with the main asteroid belt,
although it's orbit grazes Saturn before returning to the main asteroid
belt, and could be seen as an asteroid model of a SL9 type scenario
with a different outcome so far. Certainly neither Hidalgo nor SL9 has
a shared recent history with other favorite passive asteroids like
Ceres or Vesta, but we can agree that all asteroids do not share
genetics, and then there is chaotic dynamics to deal with.
My comments regarding the perturbations of the orbit (which was
proposed as much more main belt appearing than main belt asteroid
Hidalgo), were the gravitational interactions interactions with Jupiter
and this is what I perceive to be of meteoritical relevance. The
capture in the likely scenario20looks a really whole lot like Jupiter's
pull which creates the Kirkwood gaps!
In my favorite example of the main belt asteroid 944 also known as the
Ingenious Don Hidalgo y Costilla, the steep inclination of Hidalgo is
thought to be from a close call after charging the Jovian gravitational
windmill. Luckily, Hidalgo Lives. Viva Hidalgo! When Hidalgo is
closest to the Sun in the inner main asteroid belt, a very weak coma is
suggested. As I mentioned, the "how" of an object getting to where it
is before it eases into its new zone is a great question for just about
everything.
It was me who used the word "dramatic" to characterize your
description, "Probably a captured comet that happened to come too close
to Jupiter on its first pass ... into the inner part of the Solar
System." That, I would consider an extremely dramatic and highly cool
as unlikely scenario. My reply served to downplay this to consider
like in the fast lane of the asteroid belt and the effects of mny years
of Jupiter-Kirkwood type interactions which iseems the simpler
explanation in this case. that is, to Think Hidalgo ... and allow
contencious nomenclature a back seat to the spotlight on location and
mechanics, even with cross-overs. From your followup, I don't think
you would disagree with this, so maybe after much ado, we're both fine
with it.
Finally, I hope you noted that I support your ideas of plan
etary
roulette and then, raise them more, of the overblown comet collision
proponents, which was IMO the most interesting meteoritite-related
comment of my post which escaped your and other's comment, much to the
disappointment of little me. That Japanese paper makes me jealous just
looking at how beautiful an analysis of collision probabilities can be
and how much there is to be learned to develop such elegance in
solutions by amateurs (speaking for myself, really). Earth, every 2 to
4 million years ... I wonder what the dinosaurs were thinking ... why
us!!!!! why! why!
best wishes, and great health,
Doug
-----Original Message-----
From: [email protected]
To: [email protected]
Cc: [email protected]
Sent: Sun, 11 Jan 2009 12:09 pm
Subject: Re: [meteorite-list] Comet smashes triggered ancient famine ???
Hi Doug:
This is one of many models for the capture and a very possible one.
However, from what I see of the obital evolution and the actual
abstract,
I would say that prior to capture, in this model, SL9 was a Jupiter
family
comet which is a far cry from an asteroid belt object (had to come close
to Jupiter multiple times).
The asteroid belt goes out to 3.3 AU, so not with nearly 2 AU of
Jupiter,
not like the pre-capture SL9.
Larry
PS Never said it was a dramatic capture!
On Sun, January 11, 2009 10:50 am, [email protected] wrote:
Larry wrote:
"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."
Hi Larry, Listees,
IMO, it was far from that dramatic sort of initial Jovian fishing
expedition in those passes, in that SL9, before it's chaotic Jupiter
capture looked like one of our favorite kinds of asteroids with an
orbit
likely CONFINED inside the main asteroid belt and with sufficiently
of low
inclination (though with lower probability it could have been stuck a
little further out, at most, into the zone between Jupiter and
Saturn).
While all short period comets like SLP have a
pinball aspect to their orbits before getting stuck within, say,
inside
Neptune's orbit, SL9 just did what any meteoroid with potential would
have done in that it got too close to Jupiter and stretched out its
orbit
like pulling a rubber band. As this is thought to have happened
right at
aphelion, the comet was basically at a standstill when Jupiter
bumbled by
and it transferred into a Jovian orbit by basically falling into
Jupiter
in an extremely eccentric orbit (as you point out), and from there on,
just got too close to Jupiter as Jupiter and the Sun ironed out tyheir
differences20without JPL pushing the comet's outgassing buttons.
Here is a sc
ienific eplanation and a graphical evolution of the capture orbits as
calculated by astrophysicists: http://tinyurl.com/742lbr
Of course, where SL9, or anything else for that matter before being in
the e.g., asteroid belt, came from, whether 25 or 2.5 billion years
earlier, makes for good philosophy.
A minor sampling of thoughts on this event from a meteoritical
perspective...and for all good hearted Comet-fearing humans:
The collision of SL9 with Jupiter was a great event to have been alive
to have observed, but should be put in the appropriate context
regarding
orbit dynamics and the inner Solar system (read: frequencies of
collision
with Earth). While such a Jupiter collision may well be a once in
6000
(as you suggested) year event, one very pleasing rigorous
analysis concluded that such event:
" In particular, we show that, for Jupiter-interacting* comets of
greater than 1 km diameter, a Jupiter impact takes place every 500 to
1000
years, and an Earth impact every 2 to 4 million years."
The sort of study great pops the ballon of theories suggesting that
comets frequently strike Earth (and shape evolution frequently in
thousands
or tens of thousands of years periods). The important detail lies
within
the observation that the residence time for comets in the Terrestrial
(inn
er) Solar system is so short and chaotic from an
orbital perspective, and the planets so small (for example, see
Larry's
cross section , but he was actually waaaaay overestimating it since we
need to also consider the inclinations of the comets), that there is
virtually nil chance = 2 - 4 million years vs. what we saw happen on
Jupiter. Furthermore, what led to that collision, as has already been
suggested is that Jupiter was able to capture the comet to start
with. That
is not something the Earth is adept at doing considering the relative
size
of the Sun and its gravitational potential vs. ours in the uptown
part of
the Solar neighborhood. Here is the excellent statistical vs.
observational treatise by T. NAKAMURA (National Astronomical
Observatory,
Japan) and H. KURAHASHI (Sano-Fuji Optics
Company, Japan), THE ASTRONOMICAL JOURNAL, 115:848-854, Feb. 1998.
http://www.iop.org/EJ/article/1538-3881/115/2/848/970144.html
*ok, so have the wild card of hyperbolic comets and highly inclined
rogue comets and the likes of the kitchen sink of things that don't
fit
nicely into the Solar system intro textbook. Perhaps this provides
some
SOLice for the frequent Terrestrial-cometary collision proponents.
Anyway, this is my take on it Larry, and it is based on oldies but
goodies regarding the papers cited. I can't find, and don't know that
anyone has done anything p
articularly revolutionary since then.
Best wishes, great health and keep looking up,
Doug
-----Original Message-----
From: [email protected]
To: [email protected]
Cc:[email protected]
Sent: Sun, 11 Jan 2009 6:54 am
Subject: Re: [meteorite-list] Comet smashes triggered ancient famine
???
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).
204. 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
20take).
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 othe rs 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, [email protected] 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 <[email protected]> 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, [email protected]
<[email protected]>
wrote:
From: [email protected] <[email protected]>
Subject: Re: [meteorite-list] Comet
smashes triggered ancient famine ???
To: [email protected]
Cc: "tracy latimer" <[email protected]>,
[email protected] 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
20c.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
<[email protected]> wrote:
From: tracy latimer <[email protected]>
Subject: Re: [meteorite-list] Comet smashes
triggered ancient famine ???
To: "Paul" <[email protected]>,
[email protected]
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
0A>>
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: [email protected]
To: [email protected]
Subject: [meteorite-list] Comet smashes
triggered
ancient famine ???
Comet smashes triggered20ancient 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.
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