(meteorobs) Com 1833 S1 & Delta Cancrids

[Robert Lunsford]

David,

Very interesting reading. Thanks for sharing it with us!

Robert Lunsford

---- David Seargent <seargent at ozemail.com.au> wrote: 
> I have been intrigued by the apparent similarity between the orbits of the Delta Cancrids, the Maribo meteorite, asteroid 1991 AQ & now C/1833 S1 (Dunlop)! Much of this is presented in an on-line article at
>  
> www.taleoftwometeorites.simplesite.com
>  
> where a common origin between the Maribo and Sutter's Mill meteorites is suggested to be the original Comet Encke (sometimes called "Proto-Encke"), believed to be the progenitor of the Taurid complex. The Cosmic ray exposure age of SM appears to be not more than about 19,000 years on latest estimates, which brings it nicely in line with the widely accepted age of the Taurid stream. The CRE age of Maribo is, however, between 600,000 and 1,200,000 years, so it could not have been first exposed at the same time, although it may have been exposed on the surface of the parent object (or even in orbit around it??). In any case, the Maribo orbit puts it within the "Hephaistos group" of asteroids and meteor streams, which Steel & Asher consider an extended branch of the Taurid complex. Using Drummond's D'-criterion for comparison between its orbit and the three Delta Can. orbits given by Kronk gives values of 0.109, 0.04 and 0.07 - only the first lying just outside the critical value of 0.105. Interestingly, asteroid 1991 AQ gives values of 0.12, 0.06 and 0.08 with these three orbits and 0.04 with Maribo. This looks like a very good association, except that 1991 AQ has a QU-type reflectance spectrum and Maribo is a CM2 meteorite! Either AQ is an interloper and the "association" is mere coincidence (which seems a bit farfetched given the small D' value) or it is essentially a CM-type object that has formed a lighter coloured crust (but then, why should the crust be from material so atypical of its bulk composition?) or it was a large "xenolith" of asteroidal composition incorporated into the true parent body. 
> This brings us to C/1833 S1. Although the orbit is usually given as a parabola, a short-period ellipse also fits the observations and a period as short as 3.5 years has been suggested (presumably, in 1833 it was in outburst and has since faded out). If that is true, a D' comparison with the three  Delta Can. orbits yields values of 0.08, 0.06 and 0.06, with Maribo of 0.07 and with 1991 AQ, 0.05.
> A short-period orbit seems compatible with a Proto-Encke origin, but if 1833 S1 really is long period (perhaps several tens or even hundreds of thousands of years) the presence of 1991 AQ and Maribo might indicate a major disruption events near perihelion 5, 10, 20 or more revolutions past, (equal to the CRE age of Maribo) leaving several large masses in short-period orbits. The main nucleus fragment remains an active long-period comet that continues to shed meteoroids into the Delta Cancrid stream. Indeed, there may even be several fragments, although there is no evidence for this to date. The apparent Taurid association would then be coincidental, presumably.
> Clear skies,
> David Seargent
>