C/1998 P1 Williams
more info
Comet C/1998 P1 was discovered on 10 August 1998 by Peter Williams (Heathcote, Australia). At the moment of discovery, C/1998 P1 was about 2 months before its perihelion passage and it was last observed in the mid-May 1999.
Comet had its closest approach to the Earth on 28 July 1998 (0.887 au), about 2 weeks before its discovery.
This is a comet with nongravitational effects strongly manifested in positional data fitting.
Solutions given here are based on data spanning over 0.758 yr in a range of heliocentric distances: 1.56 au – 1.15 au (perihelion) – 3.13 au.
This comet suffers large planetary perturbations during its passage through the planetary system; these perturbations lead to a significantly more tight future orbit with semimajor axis of about 830 au. See also Królikowska 2020.

solution description
number of observations 461
data interval 1998 08 11 – 1999 05 15
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 1.56 au – 1.15 au (perihelion) – 3.13 au
type of model of motion NS - non-gravitational orbits for standard g(r)
data weighting YES
number of residuals 905
RMS [arcseconds] 0.78
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 1998 11 03
perihelion date 1998 10 17.84544629 ± 0.00011566
perihelion distance [au] 1.14620268 ± 0.00000306
eccentricity 0.99874253 ± 0.00000838
argument of perihelion [°] 294.467428 ± 0.000175
ascending node [°] 156.370816 ± 0.000071
inclination [°] 145.727403 ± 0.000048
reciprocal semi-major axis [10-6 au-1] 1,097.08 ± 7.31
Upper panel: 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.
Lower panel (panels): O-C diagram for this(two) solution (solutions) given in this database, where residuals in right ascension are shown using magenta dots and in declination by blue open circles.
non-gravitational parameters
A1 [10-8au/day2] 31.566 ± 0.24
A2 [10-8au/day2] 1.6652 ± 0.0925
A3 [10-8au/day2] -1.055 ± 0.0316
m -2.15
n 5.093
k -4.6142
r0 [au] 2.808
α 0.1113