C/2017 K2 PANSTARRS
more info
Comet C/2017 K2 was discovered on 21 May 2017 by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Hawaii when it was 16.1 au from the Sun. Later, almost twenty pre-discovery measurements dating back to 2013 May 12 were found, the first series of measurements was taken at the heliocentric distance of almost 24 au. These prediscovery data series are separated by one large gap of about 2.5 yr and two shorter gaps of about six months and eight months, respectively. Since the discovery the comet has been observed almost continuously (and is still observable).
Comet will have its closest approach to the Earth on 14 July 2022 (1.81 au), about 5 months before its perihelion passage (1.80 au from the Sun on 19 December 2022).
Solutions given here are based on pre-perihelion data and different data-arcs, for more see respective solutions; the longest data arc is spanning over 8.90 yr in a range of heliocentric distances from 23.74 au to 3.52 au (7 April 2022)

More details in Królikowska and Dybczyński 2018 and Dybczyński and Królikowska 2022 (or Dybczyński and Królikowska 2022).

solution description
number of observations 3757
data interval 2013 05 12 – 2020 11 13
data arc selection data generally limited to pre-perihelion (PRE)
range of heliocentric distances 23.74 au – 7.81au
type of model of motion NC - non-gravitational orbits for symmetric CO-g(r)-like function
data weighting YES
number of residuals 7373
RMS [arcseconds] 0.36
orbit quality class 1a+
orbital elements (heliocentric ecliptic J2000)
Epoch 2018 11 18
perihelion date 2022 12 20.65281903 ± 0.00204548
perihelion distance [au] 1.80553696 ± 0.00000452
eccentricity 1.00036069 ± 0.00000143
argument of perihelion [°] 236.079695 ± 0.000134
ascending node [°] 88.256848 ± 0.000033
inclination [°] 87.54409 ± 0.000006
recip semi-major axis [10-6 au-1] -199.77 ± 0.79
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.
Middle panel(s): O-C diagram for a given solution (sometimes in comparison to another solution available in CODE), where residuals in right ascension are shown using magenta dots and in declination by blue open circles.
Lowest panel: Relative weights for a given data set(s).
non-gravitational parameters
A1 [10-8au/day2] 28.414 ± 4.968
A2 [10-8au/day2] 11.61 ± 1.089
A3 [10-8au/day2] 4.5795 ± 0.7221
m -2.00
n 3.000
k -2.6000
r0 [au] 10.000
α 0.0100