C/2017 S7 Lemmon
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Comet C/2017 S7 was discovered on 26 September 2017 with Mount Lemmon survey, that is about 4 months after its perihelion passage. Several prediscovery images of this comet were found: taken by the same survey from 18, 27 and 30 of December 2016. This comet was observed until 15 November 2018.
Comet had its closest approach to the Earth on 18 December 2016 (6.698 au), exactly the same day as the first pre-discovery image were taken; almost 5.5 months before its perihelion passage.
Solution given here is based on data spanning over 1.91 yr in a range of heliocentric distances: 7.68 au – 7.615 au (perihelion) – 8.31 au.
This marginally Oort spike comet suffers insignificant planetary perturbations during its passage through the planetary system.

solution description
number of observations 153
data interval 2016 12 18 – 2018 11 15
data type perihelion within the observation arc (FULL)
data arc selection entire data set (STD)
range of heliocentric distances 7.68 au – 7.62 au (perihelion) – 8.31 au
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 298
RMS [arcseconds] 0.37
orbit quality class 1a
orbital elements (heliocentric ecliptic J2000)
Epoch 2017 06 16
perihelion date 2017 05 27.97757714 ± 0.00456201
perihelion distance [au] 7.61440553 ± 0.00001021
eccentricity 1.00230740 ± 0.00000941
argument of perihelion [°] 187.752935 ± 0.000314
ascending node [°] 262.786942 ± 0.000022
inclination [°] 124.219818 ± 0.000045
recip semi-major axis [10-6 au-1] -303.03 ± 1.23
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