C/1999 S2 McNaught-Watson
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C/1999 S2 was discovered on 19 September 1999 by Robert H. McNaught on an R-survey film taken by F.G. Watson using UK Schmidt Telescope, 1.8 yr after perihelion passage.
This comet made its closest approach to the Earth on 20 June 1997 (5.670 au), 5 months before perihelion.
Solution given here is based on data spanning over 2.4 yr in a range of heliocentric distances from 7.84 au to 11.7 au.
This Oort spike comet suffers moderate planetary perturbations during its passage through the planetary system that lead to escape of the comet from the solar system on hiperbolic orbit (see future barycentric orbit).
See also Królikowska 2014 and Królikowska and Dybczyński 2017.

solution description
number of observations 98
data interval 1999 09 19 – 2002 02 16
data type observed only after perihelion (POST)
data arc selection entire data set (STD)
range of heliocentric distances 7.84 au – 11.7au
detectability of NG effects in the comet's motion NG effects not determinable
type of model of motion GR - gravitational orbit
data weighting YES
number of residuals 184
RMS [arcseconds] 0.48
orbit quality class 1a
orbital elements (heliocentric ecliptic J2000)
Epoch 1997 11 08
perihelion date 1997 11 22.53221900 ± 0.00648700
perihelion distance [au] 6.46669745 ± 0.00004864
eccentricity 1.00725540 ± 0.00002471
argument of perihelion [°] 223.477051 ± 0.000614
ascending node [°] 74.427229 ± 0.000142
inclination [°] 65.81313 ± 0.000028
recip semi-major axis [10-6 au-1] -1,121.96 ± 3.82
Time distribution of positional observations with corresponding heliocentric (red curve) and geocentric (green curve) distance at which they were taken. The horizontal dotted line shows the perihelion distance for a given comet whereas vertical dotted line – the moment of perihelion passage