No Subject

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.

Brian G. Marsden

=========================
(2) ANOTHER FIREBALL OBSERVATION ON 22 APRIL OVER WASHINGTON STATE & 
    BRITISH COLUMBIA

---

• Prev by Date: No Subject
• Next by Date: No Subject
• Prev by thread: No Subject
• Next by thread: No Subject
• Index(es):
  • Main
  • Thread