  Comets are classified from their orbital characteristics into two separate
classes: nearly-isotropic, mainly long-period comets and ecliptic, short-period
comets. Members from the former class are coming from the Oort cloud. Those of
the latter class were first believed to have migrated from the Kuiper belt
where they could have been accreted in situ, but recent orbital evolution
simulations showed that they rather come from the trans-Neptunian scattered
disc. These two reservoirs are not where the comets formed: they were expelled
from the inner Solar System following interaction with the giant planets. If
comets formed at different places in the Solar System, one would expect they
show different chemical and physical properties. In the present paper, I review
which differences are effectively observed: chemical and isotopic compositions,
spin temperatures, dust particle properties, nucleus properties... and
investigate whether these differences are correlated with the different
dynamical classes. The difficulty of such a study is that long-period,
nearly-isotropic comets from the Oort cloud are better known, from Earth-based
observations, than the weak nearly-isotropic, short-period comets. On the other
hand, only the latter are easily accessed by space missions.
