23 February 2017 - Mission Day: 7755 - DOY: 054

Family Ties Among a Thousand Comets

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      observations of comet 96P Machholz
Comet 96P/Machholz 1, likely related to the family (below) in the Marsden group
See this Hot Shot for movies and more information.

The suspected relationships among 9 Marsden-group comets
Suspected relationships among 9 Marsden-group comets observed by LASCO.

Family movies (animated GIFs): C/2004 V9 and V10, C/2005 E4, C/2005 G2.

With only 10 to go until SOHO's one thousandth comet has been discovered (see related links below), there are still surprises to be encountered: The so-called "Marsden group" of comets appears to contain a close-knit family tree!

Nine comets observed by SOHO (C/1999 P6, P8, P9, N5 and J6, C/2005 E4, G2, V9 and V10) are believed to make up two successive generations of this family tree, shown above with a supposed (not observed) "grandparent" that might have travelled near the Sun in 1993. The "X" indicates that no return of C/1999 P6, P8 or P9 (nor children) was observed. Presumably, they did not "survive" the 1999 encounter with the Sun (all of their ice evaporated) or they were simply below the brighness level detectable with LASCO in April/May of 2005.

Comet groups, and "families" like the one shown above, are the result of fragmentation of the "parent bodies" near perihelion (the closest approach to the Sun).

But the small family above is not the end of the story - there are many other likely links between the almost one thousand comets observed by SOHO: Comet 96P/Machholz 1 - observed by SOHO in 1996 and 2002 (a much more photogenic comet, as shown in the montage above) may be the ancestor not only of the Marsden group of comets but also of the Kracht I group. The relationship between the Marsden and Kracht I groups is fairly obvious from the striking similarity of their orbits - the link to 96P/Machholz 1 is harder to show, and may go about 4000 years back in time.

There's more - the Marsden and Kracht I groups, together with 96P/Machholz 1 may also be related to several meteor showers: The closest link is between Marsden, Kracht I and the Daytime Arietids. More distant links may exist also to the Quadrantids and the Delta Aquarids meteor showers.

At the risk of overselling a point - that's still not all. The Kreutz group of sungrazer comets also have a noble (though different) lineage, if you believe the claims quoted in a nice article on this subject by Tony Hoffman and Brian G. Marsden in the August 2005 edition of Sky & Telescope. The two subgroups of Kreutz comets (I and II) themselves contain the Great Comet of 1843 (Kreutz I) and the Great Comet of 1882 as well as Ikeya-Seki (Kreutz II). The latter two may be the result of a splitting of the AD 1106 comet. And perhaps (though not supported by much evidence), they're all related to a comet reported to be seen splitting in 372 BC by Greek philosopher Ephorus!

Now that is something to ponder about while waiting for SOHO-1000 to be announced!

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