[meteorite-list] BREAK! For the love of meteorites, STOP -- COMET 73/P

From: joseph_town_at_att.net <joseph_town_at_meteoritecentral.com>
Date: Sun May 14 17:52:04 2006
Message-ID: <051420062152.17399.4467A67E00039B92000043F721603760210299019BA1089F0A9C0106_at_att.net>

Pete Pete,

Not to slight all the experts on the met-list, try http://www.meteorobs.org. They are hardcore specialists.

Bill



 -------------- Original message ----------------------
From: "Pete Pete" <rsvp321_at_hotmail.com>
> Hi, Sterling and Doug,
>
> Thanks for your valued input.
>
> Regarding the 2022 shower, I was wondering how different that spectacle will
> be considering it won't be the normal dust-to-pea-sized coma debris, but
> more likely some considerable chunks included, due to the current and nicely
> timed disintegration.
>
> Armegaddon!? What side of the planet should we be on then? (-Rhetorical ;])
>
> At this rate of break-up, is it possible that there won't be a comet left
> for a return trip from around the sun?
>
> Cheers,
> Pete
>
>
> From: "Sterling K. Webb" <sterling_k_webb_at_sbcglobal.net>
> To: "Meteorite List"
> <meteorite-list_at_meteoritecentral.com>,<joseph_town@att.net>,"Pete Pete"
> <rsvp321_at_hotmail.com>
> Subject: Re: [meteorite-list] BREAK! For the love of meteorites, STOP --
> COMET 73/P
> Date: Sun, 14 May 2006 03:08:50 -0500
>
> Hi, Pete,
>
> Your message came just in time. I was typing a snide remark
> about the Hematitic Lump From Mars. (Somebody forward to
> this guy Göran Axelsson's picture of the identical "tone rock"
> in Sweden at a church, and explain to the guy that he got God's
> message all mixed up -- he's supposed to use his rock as the
> bell for his church, not sell it on eBay!)
>
> What bothers me about Comet 73P is this: It can't be a
> "new" comet (even though we discovered it in 1930). The orbit
> is too stable for the comet to have recently been thrown in
> there. It's been around for centuries, probably millennia, in
> this same orbit. Yet, it has unraveled so quickly and easily.
>
> Once it started to come apart, sometime between 1990
> and 1995, it has split, re-split, fractured. If you go back and
> read the earliest studies this pass, the authors clearly expected
> that whatever splits had occured at the time they wrote to
> be the extent of splitting when they passed the Earth.
>
> Three fragments would be visible, they said. Whoops, make
> that six fragments. Uh-oh, make that 9, 12, 30. I'm not making fun
> of the researchers, but our experience of split comets is that
> this disintegration takes a while. 73P has just gone to hell
> overnight. It must be very, very weak, they say.
>
> OK, BUT... If it's that weak, what has been holding it
> together for the last 75 years (and for centuries before
> that)? Thermal stress is pegged as the likely culprit for the
> breakup, but it's been exposed to the Sun for a long time.
> How could it have survived so long if it was this fragile?
>
> My guess answer is that the fragile material was probably
> adhered to something that wasn't fragile, like a small rocky core.
> This small dark object would have been completely shielded
> from the Sun by the weak porous fluffy ices that surrounded
> it and made up the outer body of the comet.
>
> But once a good chunk of those ices cracks off from a tiny
> impact or from thermal stress, it exposes a portion of the dark
> rock core to sunlight; the rock warms and more fragments of
> icy fluff soon come loose. They're too small to survive and rapidly
> break up in a cascade of fragments, as we've seen. A bare dark
> rock object is left behind in an orbit similar to the other fragments,
> but it's too distant to be detected... yet.
>
> I'm looking forward to the discovery of a small Earth-crossing
> asteroid in 2011, 2016, 2022 with an orbit very like Comet 73P!
> It would not be a big one. The pre-breakup 73P nucleus was only
> 1000-1200 feet in diameter; a core is unlikely to be more than
> a few hundred feet across (30 to 80 meters), I hope, instead of
> 400 meters.
>
> Despite the fact that meteor showers are so showy, no fall
> has ever been associated with them. Only one fall was ever
> witnessed during a meteor shower and recovered, and it
> was an iron, a complete coincidence. The biggest fragments
> in a meteor shower are smaller than a pea, moving very fast,
> and in for a short bright ride, then Pffft! Small junk never
> makes it through the atmosphere.
>
> Predicting future meteor shower orbits is the most thankless
> job in number crunching. Some people like it for that very
> reason. Every little piece of cometary material is capable of
> puffing little jets of gas; every little jet is a thrust; every thrust
> alters the precise orbit somewhat; the thrusts go on for months
> with progressive orbital changes, like ion engines. Some jets
> are on rotating bodies, so the thrusts are like pinwheel jets,
> pushing this way then that way. To quote Charlton Heston
> in Planet of the Apes, "It's a madhouse! A madhouse!"
>
> How spectacular a close comet approach is depends
> not only on how close but on how big. The close approach
> of a really big fresh long-period comet is probably the most
> spectacular thing that is visible in the sky, apart from a
> Type II supernova 700 light years away. We haven't had
> one really spectacular one for over a century and a half,
> but the century before that was blessed with some giant
> "apparitions," as they are called, in 1729 and 1744,
> and the 19th century had flashier big meteor showers
> than the 20th. Maybe we're due for one.
>
> As for people who worry about close approaches,
> here's a table of the 20 closest approaches of comets
> that were discovered after 1700 (although some historical
> close approaches are included in the list), courtesy of
> Harvard http://cfa-www.harvard.edu/iau/lists/ClosestComets.html
> One of the brightest recent ones is Hyakutake in
> 1996 and it was a really fine sight. Comet 73P is on
> the list at Number Ten (in 1930 when it was discovered).
>
> I added the distance to the Moon for comparison, and
> in all this time, nothing has gotten closer than six times the
> Moon's distance.
>
> I say, let's keep it that way.
>
> Distance Date (TT) Permanent designation
> (AU)
> 0.0026 Distance to the Moon
> 0.0151 1770 July 1.7 D/1770 L1 (Lexell)
> 0.0229 1366 Oct. 26.4 55P/1366 U1 (Tempel-Tuttle)
> 0.0312 1983 May 11.5 C/1983 H1 (IRAS-Araki-Alcock)
> 0.0334 837 Apr. 10.5 1P/837 F1 (Halley)
> 0.0366 1805 Dec. 9.9 3D/1805 V1 (Biela)
> 0.0390 1743 Feb. 8.9 C/1743 C1
> 0.0394 1927 June 26.8 7P/Pons-Winnecke
> 0.0437 1702 Apr. 20.2 C/1702 H1
> 0.0617 1930 May 31.7 73P/1930 J1 (Schwassmann-Wachmann 3)
> 0.0628 1983 June 12.8 C/1983 J1 (Sugano-Saigusa-Fujikawa)
> 0.0682 1760 Jan. 8.2 C/1760 A1 (Great comet)
> 0.0839 1853 Apr. 29.1 C/1853 G1 (Schweizer)
> 0.0879 1797 Aug. 16.5 C/1797 P1 (Bouvard-Herschel)
> 0.0884 374 Apr. 1.9 1P/374 E1 (Halley)
> 0.0898 607 Apr. 19.2 1P/607 H1 (Halley)
> 0.0934 1763 Sept.23.7 C/1763 S1 (Messier)
> 0.0964 1864 Aug. 8.4 C/1864 N1 (Tempel)
> 0.0982 1862 July 4.6 C/1862 N1 (Schmidt)
> 0.1018 1996 Mar. 25.3 C/1996 B2 (Hyakutake)
> 0.1019 1961 Nov. 15.2 C/1961 T1 (Seki)
> Sterling K. Webb
> -------------------------------------------------------------------------
> ----- Original Message ----- From: "Pete Pete" <rsvp321_at_hotmail.com>
> To: <joseph_town_at_att.net>
> Cc: <meteorite-list_at_meteoritecentral.com>
> Sent: Saturday, May 13, 2006 11:06 PM
> Subject: RE: [meteorite-list] BREAK! For the love of meteorites, STOP
>
>
> >
> >Hello, List,
> >
> >There has been over thirty posts in this thread with barely an
> >interruption. Nothing else to talk about?
> >
>
> >I'm hoping Sterling K. Webb will give us his analytical dissection of the
> >disintegration of Comet 73P, in his usual interestingly descriptive way!
> >>From the top, Sterling!
> >And some thoughts about its predicted meteor shower in 2022, if you
> >will.(any speculation as to survivors to the surface then?)
> >http://www.space.com/scienceastronomy/060510_comet_spitzer.html
> >http://www.space.com/scienceastronomy/060510_comet_spitzer.html
> >
> >Cheers,
> >Pete
> >
>
>
Received on Sun 14 May 2006 05:52:00 PM PDT