C/2013 X1 PanSTARRS
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Comet C/2013 X1 was discovered on 4 December 2013 at the Pan-STARRS 1 observatory on Mount Haleakala in Hawaii, that is about a year and five months before its perihelion passage, and was followed until 29 January 2018. C/2013 X1 had closest approach to the Earth on 21 June 2016 (0.640 au, almost two months after the perihelion passage).

This is the comet with NG effects strongly manifested in positional data fitting. Solutions 'a5' (GR), 'n5' (NG), and t4 (asymm. NG, preferred orbit) are based on data spanning over 4.3 yr in a range of heliocentric distances: 9.25 au – 1.314 au (perihelion) – 7.17 au. Also NG orbit based on distant part of pre-perihelion leg of orbit was possible to obtain (see solution 'pd').

All solutions result in original orbit outside Oort spike with semimajor axis of about 2600–6100 au. This comet suffers moderate planetary perturbations while passing through the planetary system; these perturbations lead to escape the comet from the planetary zone on a hyperbolic orbit (see future barycentric orbits for all orbits given here).
solution description
number of observations 3324
data interval 2013 10 17 – 2018 01 29
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 9.25 au – 1.31 au (perihelion) – 7.17 au
type of model of motion NT - non-gravitational orbits for asymmetric, standard g(r)
data weighting YES
number of residuals 6569
RMS [arcseconds] 0.46
orbit quality class 1a+
orbital elements (barycentric ecliptic J2000)
Epoch 1714 04 26
perihelion date 2016 04 21.71006747 ± 0.00004784
perihelion distance [au] 1.32005812 ± 0.00000084
eccentricity 0.99962805 ± 0.00000075
argument of perihelion [°] 164.444707 ± 0.000066
ascending node [°] 130.970726 ± 0.000028
inclination [°] 163.237157 ± 0.000003
reciprocal semi-major axis [10-6 au-1] 281.77 ± 0.57
file containing 5001 VCs swarm
2013x1t4.bmi
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).
Six 2D-projections of the 6D space of original swarm including 5001 VCs. Each density map is given in logarithmic scale presented on the right in the individual panel.