  Dynamical studies of asteroid populations in retrograde orbits, that is with
orbital inclinations greater than 90 degrees, are interesting because the
origin of such orbits is still unexplained. Generally, the population of
retrograde asteroids includes mostly Centaurs and transneptunian objects
(TNOs). A special case is the near-Earth object (343158) 2009 HC82 from the
Apollo group. Another interesting object is the comet 333P/LINEAR, which for
several years was considered the second retrograde object approaching Earth.
Another comet in retrograde orbit, 161P Hartley/IRAS appears to be an object of
similar type. Thanks to the large amount of observational data for these two
comets, we tested various models of cometary non-gravitational forces applied
to their dynamics.
  The goal was to estimate which of non-gravitational perturbations could
affect the stability of retrograde bodies. In principle, we study the local
stability by measuring the divergence of nearby orbits.
  We numerically determined Lyapunov characteristic indicators (LCI) and the
associated Lyapunov times (LT). This time, our calculations were extended by
more advanced models of non-gravitational perturbations (i.e. Yarkovsky drift
and in selected cases cometary forces). This allowed us to estimate chaos in
the Lyapunov sense.
  We found that the Yarkovsky effect for obliquities of $\gamma=0^{\circ}$ and
$\gamma=180^{\circ}$ can change the LT substantially. In most cases, for the
prograde rotation, we received more stable solutions. Moreover, we confirmed
the role of retrograde resonances in this process. Additionally, the studied
cometary effects also significantly influence the long-term behaviour of the
selected comets. The LT can reach values from 100 to over 1000 years.
Conclusions. All of our results indicate that the use of models with
non-gravitational effects for retrograde bodies is clearly justified.
