**Orbital linkages between
SOHO LASCO comets**

Several possible linkages have been found between the Marsden group comets showing orbital periods of 5.3 to 6.1 years.

C/1999 J6 = C/2004 V9 (P = 5.5 years) Marsden next
perihelion 2010 May 01 (NK
1620)

The comet returned as P/2010 H3, 11.6 days earlier than expected (MPEC 2010-J28).

C/1999 N5 = C/2005 E4 (P = 5.7 years) Marsden next
perihelion 2010 October 29 (NK
1620)

C/1999 N5 = C/2005 G2 (P = 5.8 years) Marsden next
perihelion 2011 January 06 (NK
1620)

C/1996 V2 = C/2002 V5 (P = 6.0 years) Sekanina and Chodas next
return 2008 Nov 09 not
observed

(but large data gaps during the days after the predicted
perihelion - SOHO 34m keyhole November 08 - 19).

C/2000 C4 = C/2005 W1 (P = 5.8 years) Marsden next
perihelion 2011 August 17 (NK
1620)

C/1999 U2 = C/2005 W5 (P = 6.1 years) Marsden next
perihelion 2012 January 06 (M.Knight)

C/1999 U2 = C/2005 E4 (P = 5.4 years) Nakano next perihelion 2010 July 17

C/2002 R4 = C/2007 Y4 (P = 5.3 years) Marsden previous perihelion
1997 May 15 not observed

C/2002 R1 = C/2008 A3 (P = 5.4 years) Marsden previous perihelion
1997 April 19 not observed

C/2003 Q1 = C/2008 X6 (P = 5.3 years) Marsden previous perihelion
1998 April 26 not observed

C/2003 Q6 = C/2008 Y11 (P = 5.3 years) Marsden previous perihelion
1998 April 29 not observed

Several possible linkages have been found between the Kracht group comets showing orbital periods of 4.8 to 6.0 years.

C/2000 O3 = C/2005 W4 (P = 5.3 years) Marsden next
perihelion 2011 March 19 (M.Knight)

C/2002 Q8 = C/2008 E4 (P = 5.5 years) Marsden previous perihelion
1997 February 15 not observed

C/2002 S11 = C/2008 G6 (P = 5.5 years) Marsden previous perihelion
1997 March 17 not observed

C/2002 Q10 = C/2008 G6 (P = 5.6 years) Kracht, previous
perihelion 1997 January 07 not observed

C/2002 S7 = C/2008 N4 (P = 5.8 years) Marsden previous perihelion
several hours before C/1996 X3/X4/X5

C/2002 S4 = C/2008 R7 (P = 6.0 years) Marsden previous perihelion
1996 September 26 not observed

C/2002 S11 = C/2008 R7 (P = 5.9 years) Marsden previous perihelion
1996 October 21 not observed

C/1996 X4 = C/2002 S4 (P = 5.8 years) Kracht, next perihelion
2008 June 28 not observed

C/1996 X5 = C/2002 S5 (P = 5.8 years) Kracht, next perihelion
2008 June 30 not observed

C/1999 N6 = C/2004 J4 (P = 4.8 years) Kracht, next perihelion
2009 February 23 not observed

C/1999 M3 = C/2004 L10 (P = 5.0 years) Kracht, next perihelion 2009 May 26

"Kracht2 group"

P/1999 R1 = 2003 R5 = 2007 R5 (P = 4.0 years) Marsden next
perihelion 2011 September 07

C/2002 R5 = 2008 L6 and L7 (P = 5.8 years) Marsden and Sekanina previous perihelion
1996 November 25 not observed

non-group comets

C/1999 X3 = 2004 E2 = 2008 K10 (P = 4.2 years) Marsden next
perihelion 2012

C/2001 D1 = 2004 X7 = 2008 S2 (P = 3.8 years) Marsden previous perihelion
1997 May 01 (=1997 J6) Marsden

**Details:**

**P/2007 R5** was successfully predicted by
S. Hönig with a perihelion time of 2007 September 11.263. MPEC
2007-S16 has a common orbit (using only the observations in
C2) for the three apparitions with T = 2007 September 11.320
(only a little more than one hour later than Hönig's prediction)
but it was noted that the C3 observations from 2007 increasingly
deviate of the computed position.Earlier B. Marsden had noted
"a well-known inconsistency between the C3 and C2
observations" (MPEC
2004-X73). S. Nakano derived a similar orbit
not excluding the observations in C3 with T = 2007 September
11.319.

Using all observations of C/1999 R1 and C/2003 R5 (without
excluding any observation and without using weights for the
observations) and iterating the semimajor axis until the RMS of
the residuals is smallest with EXORB 6.5 the predicted time (with
SOLEX 10.0) of the next perihelion is 2007 September 11.328.
That's only 12 and 13 minutes later than the times computed by
Marsden and Nakano including the actual observation of C/2007 R5.

I could link the orbits of **C/2008 K10** and
C/2004 E2 with a previous perihelion time of 1999 December 12.98.
The orbital elements for C/1999 X3 (MPEC
2006-L20) gave a perihelion time of 1999 December 12.67. The
three comets have very small observed arcs (0.11, 0.12, 0.16
days) being visible for not more than four hours in C2. The final
solution (MPEC
2008-S49) has a perihelion time of 1999 December 12.88 for
C/1999 X3. This is 2.4 hours earlier than my result from C/2004
E2 = 2008 K10. For comparison: the observed arcs of C/1999 R1 and
C/2003 R5 were both 1.37 days.

My linkage of **C/2008 S2** with C/2004 X7 from
my own measurements of the new comet gave a previous perihelion
time of 2001 February 18.59. The orbital elements for C/2001 D1 (MPEC
2002-O27) gave a perihelion time of 2001 February 19.01. I
found additional images of C/2001 D1 and with new measurements of
all C/2001 D1 positions the new perihelion time of C/2001 D1 was
2001 February 18.85 (MPEC
2008-S81). Together with the new measurements of C/2001 D1
the measurements of the new comet C/2008 S2 were published.
Linking the MPEC positions of C/2004 X7 and C/2008 S2 the
previous perihelion time is 2001 February 18.81. The final
solution linking all three comets (MPEC
2008-S82) for the perihelion time of C/2001 D1 is 2001
February 18.77. This is only about one hours earlier than the
result from C/2004 X7 = C/2008 S2. The observed arcs for the
latter two comets are 0.25 and 0.57 days.

These are the first three examples of SOHO LASCO comets
observed at three apparitions. From these examples it seems that
the perihelion times of the next/previous apparition can be
determined with an accuracy of about 0 to 2 hours from the
linkage of two apparitions depending on the length of the
observed arcs. For P/1999 R1 = 2003 R5 (arcs 1.37 and 1.37 days)
we have an error of 0.057 days (Hönig) and 0.008 days (Kracht)
for the next return, for C/2004 X7 = 2008 S2 (arcs 0.25 and 0.57
days) we have an error of 0.04 days (Kracht) for the previous
return, and for C/2004 E2 = 2008 K10 (arcs 0.12 and 0.16 days) we
have an error of 0.10 days (Kracht) for the previous return. No
nongravitational forces were required for these linkages of three
consecutive apparitions.

With the precovery of C/1997 J6 (= 2001 D1 = 2004 X7 = 2008 S2)
we are seeing for the first time that small nongravitational
forces are required for the linkage of four apparitions.

previous perihelion not observed ("Kracht2" group)

The previous perihelion time for **C/2002 R5 = 2008 L6**
is 1996 November 25.335. The comet crossed the LASCO C2 field
from T-5.5h to T+6.5h, that is from 1996 Nov 25 02:30 to 14:30
UTC. It should have been well visible when it left the C2 field
after perihelion with a magnitude of about mag 6, but I have
found nothing in those images! The comet must have been inactive
at that time. It became visible after it split ("most
probably between two to ten weeks before the 2002
perihelion" IAUC 8983).

next perihelion not observed (Marsden group)

The next perihelion time for **C/1996 V2 = C/2002 V5** was 2008 November
09. These comets are the two Marsden group comets with the
largest orbital inclinations. No trace of this comet has been
found in 2008 though the apparent path through C2 and C3 was
almost the same as in 1996 and 2002.

Brightness measurements by M. Knight: C/1996 V2 (black dots) and
C/2002 V5 (red dots)

These are the observed magnitudes with small corrections for
distances and no corrections for phase angle (as the viewing
geometry was almost the same in 1996 and 2002).

Magnitudes with errors of more than mag 0.5 and vignetting
factors of more than 2.51 are omitted.

The C2 observations are at left (before perihelion) and the C3
observations are at right (after perihelion).

Striking is the scatter of C2 magnitudes in 2002 (no C2 images were taken in 1996), but most measurements are between mag 7 and 8. The C3 observations of 1996 and 2002 agree well, but are rather faint. This comet has become inactive or split into pieces too small to be observed.

previous perihelion not observed (Marsden group)

April is not a good month to find Marsden group comets. Only a
short arc of the apparent path crosses the C2 field before
perihelion and this is just there where the shadow of the pylon
causes strong vignetting. The observing conditions are a better
in May, so one can ask where is the precursor of **C/2002
R4 = C/2007 Y4**? It left the C2 field about 3 hours
before perihelion on 1997 May 15, but was not observed. M.
Knight's measurements of C/2002 R4 show apparent magnitudes
around mag 8 before perihelion passage.