According to BAA comet info

Forums Comets Orbital Period of C/2020 F3 (NEOWISE) According to BAA comet info

James Lancashire

According to BAA comet info (JDS) the comet was discovered on 2020 Mar 27 so we have just 4 months of observations out of 4200 or 6800 years.

I suspect the ‘increase’ in orbital period is simply due to a longer arc of observations which has revised the orbital elements rather than genuine non-gravitational effects around perihelion.

According to in-the-sky the inclination is 129deg so the comet will hardly encounter planets for perturbations. And with semi-major axis at 364AU it will very quickly be well away from the plane of the solar system, plus very hard to detect!

Playing with in-they-sky’s orbit diagram, perihelion was ‘superior’ (and for all ‘inner’ planets). The comet passes through descending node outside Mars approx Oct 2020 which is well away from all the planets’ positions. So it’s a gravitational orbit till next perihelion!