Central Bureau for Astronomical Telegrams
IAUC 6879: P/1998 G1; C/1998 G2; 1997 XF11
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Circular No. 6879
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html
Phone 617-495-7244/7440/7444 (for emergency use only)
COMET P/1998 G1 (LINEAR)
Continuing orbit computations, mainly by S. Nakano and the
undersigned, show that this object is of Halley type. The orbital
elements on MPEC 1998-H04 have P = 41.5 years. D. DeGraff remarks that
his coaddition of CCD frames obtained on Apr. 6.1 UT by A. C. Schwortz
and himself with the 0.81-m reflector at the Alfred University Observatory
appears to confirm the presence of the tail reported on IAUC 6863. The
feature was in p.a. about 100 deg, the shorter length of 10" probably
being due to the presence of the moon nearby.
COMET C/1998 G2 (SOHO)
C. St. Cyr, Naval Research Laboratory, on behalf of the SOHO-LASCO
Consortium (cf. IAUC 6685), reports the discovery by D. Biesecker of
a comet, tailless and no brighter than mag 6, in C2 coronagraphic data.
This comet appears to have been obscured by the occulting disk pylon in
the C3 coronagraph and was not detected. Details are on MPEC 1998-H05.
1998 UT R.A. (2000) Decl.
Apr. 2.080 0 52.2 + 4 02
1997 XF11
The estimate by the undersigned on IAUC 6837 that passage within
0.002 AU of the earth on 2028 Oct. 26 was "virtually certain" was
incorrect; this was a 1-sigma miss distance, and detailed computations
allowed miss distances of up to 0.02-0.03 AU. The nominal miss distance
and error by D. Yeomans and P. Chodas (see also IAUC 6839) should have
been given as 0.00058 (+ 0.00892 / - 0.00039) AU (3 sigma on the plus side),
and K. Muinonen early remarked on a 10-percent chance for a miss by more
than the lunar distance. All concerned, including E. Bowell, agree that in
the absence of effects that would be highly unusual there was no possibility
of an earth encounter within 0.00019-0.00021 AU; Chodas remarks (and the
undersigned agrees) that this was already evident with the issuance of
MPEC 1997-Y11. Nevertheless, the likelihood of an unusually close approach
in 2028 was also clear already in Dec. 1997, and it is unfortunate that
there was not then greater awareness of this, for the recognition of 1990
observations (also found by Bowell on films taken by C. S. and E. M.
Shoemaker) would have been possible at an earlier date and physical
observations may have been attempted. Given the Helin-Lawrence 1990
measurements, simultaneous computations by G. V. Williams and by Chodas
immediately made it clear to all concerned that the 2028 miss distance
would be in the range 0.006-0.007 AU.
(C) Copyright 1998 CBAT
1998 April 18 (6879) Brian G. Marsden
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