  In recent work (Milgrom 2009, Blanchet & Novak 2011), the authors showed that
MOdified Newton Dynamics (MOND) have a non-negligible secular perturbation
effect on planets with large semi-major axes (gaseous planets) in the Solar
System. Some comets also have a very eccentric orbit with a large semi-major
axis (Halley family comets) going far away from the Sun (more than 15 AU) in a
low acceleration regime where they would be subject to MOND perturbation. They
also approach the Sun very closely (less than 3 AU) and are affected by the
sublimation of ices from their nucleus, triggering so-called non-gravitational
forces. The main goal of this paper is to investigate the effect of MOND
perturbation on three comets with various orbital elements (2P/Encke, 1P/Halley
and 153P/Ikeya-Zhang) and then compare it to the non-gravitational
perturbations. It is motivated by the fact that when fitting an outgassing
model for a comet, we have to take into account all of the small perturbing
effects to avoid absorbing these effects into the non-gravitational parameters.
Otherwise, we could derive a completely wrong estimation of the outgassing. For
this work, we use six different forms of MOND functions and compute the secular
variations of the orbital elements due to MOND and non-gravitational
perturbations. We show that, for comets with large semi-major axis, the MONDian
effects are not negligible compared to the non-gravitational perturbations.
