(meteorobs) New possible parent comet

[Robert McNaught]

Hi Roberto (Mikhail, Denis, Marko),

Roberto wrote,
> Very interesting! I have in my data base of old meteor showers
> a meteor rain the 25 July of a year between 562-568 A.C. and the
> comet C\568 O1 has orbital elements similar to to C\2004 R1! And
> 568 O 1 was at perielium the 27.7 August 568, perharps we can see
> only passage near the Earth? I shall verify my data base of sources
> this week-end.

As the person lucky enough to have been in the right place at the right
time, I have a keen interest in this ;)  It is most unlikely that 
this comet has been in an orbit even remotely resembling the current
one prior to 1990.  A couple of days ago Brian Marsden pointed out to me
that the nominal orbit has a close approach to Jupiter of 0.01 AU in that
year, and this would dramatically change the orbit.  It will be a
considerable time, if possible at all, before the current orbit is accurate
enough to define an orbit prior to 1990.  More to the point, any
existing dust in the original orbit would not be perturbed onto the
same orbit as the comet (unless in the immediate visinity of the comet
and having the same motion).  However if the comet (or asteroid) was 
disrupted during close encounter with Jupiter, then there could have
been a substantial burst of dust created at that instant.

The question of activity post 1990 will depend on a few things.  Firstly, 
there is the basic issue of whether the orbit will allow any dust trails to 
come close to the Earth.  The current orbit is adequate to define dust trails 
that originate at this perihelion as this section of the orbit is very well 
constrained.  However, prior and future perihelion passages are still very 
uncertain and dust trails *may* be highly influenced by an uncertain 
perihelion date during other passages.

Secondly, there is the issue of a possible disruption of the comet if a 
close approach to Jupiter did indeed occur in 1990.  All I can say at the 
moment is that no other fragments have been found within several degrees
along the line-of-variation of the current orbit.  This is the line
across the sky where objects, differing only in there position within a
specific orbit, would be seen from Earth.  More extensive searches will
be made, but a formal l-o-v search would have to be widened considerably
due to the uncertainties in the Jupiter encounter conditions.  It is
really the l-o-v of the Jupiter encounter orbit that should be checked
and this is and may remain unknown.  So to a first approximation, the
searches can be conducted along and around the existing l-o-v.

Thirdly, the encounter is very shallow and the low velocity encounter
could produce meteors that occur over an extended period and from a
large diffuse radiant, or at least, a radiant that moves considerably
over the period of activity.

The nominal orbit suggests that 2015 July might be a period of possible
activity, with the nominal orbit suggesting the comet passing perihelion
around the time of encounter (well, within several months).  Again, the
nominal orbit is too uncertain for any final judgement here and a full
integration of an improved orbit would be required for the da0 to be
calculated.  However, the 2004 dust trail in 2015 (2-rev) can be calculated
accurately from the existing orbit, but not the 4-rev, 3-rev or 1-rev.

The values I calculated for the radiant at nodal passage 2004 July 18.5 UT
(RA 194  Dec -27 (2000.0)  atmospheric vel = 15 km/s) agree closely with
what Marco got from the Neslusan et al. software.

Activity may indeed be extremely low, but could occur.

Finally, although this object has a small MOID (minimum orbit
intersection distance) indicating the possibility of close encounters
with the Earth, the MOID for Jupiter is also very small.  The gravational
influence of Jupiter is likely to dominate the evolution of the orbit,
but the question remains, which planet will it "interact" with first!
Steve Chesley of JPL will be doing calculations soon to determine the
possibility of VI (virtual impactor) solutions.  Again, these are going
to be very uncertain until a more reliable orbit is calculated.

Cheers, Rob