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 NT - non-gravitational orbits for asymmetric, standard g(r)
data weighting YES
number of residuals 905
RMS [arcseconds] 0.66
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 1998 11 03
perihelion date 1998 10 17.85304103 ± 0.00033049
perihelion distance [au] 1.14635434 ± 0.00000930
eccentricity 0.99903869 ± 0.00002173
argument of perihelion [°] 294.478651 ± 0.000526
ascending node [°] 156.371729 ± 0.000108
inclination [°] 145.728174 ± 0.000067
recip semi-major axis [10-6 au-1] 838.58 ± 18.96
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\day-2] 19.546 ± 0.599
A2 [10-8au\day-2] -1.9876 ± 0.1358
A3 [10-8au\day-2] -0.54739 ± 0.03883
m -2.15
n 5.093
k -4.6142
r0 [au] 2.808
α 0.1113
ΔT [days] 33.1110 ± 2.226