  Comets are believed to be born in the outer Solar System where the
temperature is assumed to have never exceeded T ~ 100 K. Surprisingly,
observations and samples of cometary dust particles returned to Earth showed
that they are in fact made of a mix of ices, as expected, but also of materials
forged at high-temperatures (T ~ 1500 K). We propose a radically new view
regarding the origin of the high-temperature processed materials in comets,
based on the recent "Tidal Downsizing" (TD) hypothesis for planet formation. In
the latter, the outer proto-planetary disc is gravitationally unstable and
forms massive giant planet embryos (GEs). These hot (T ~ hundreds to 2000 K)
and dense regions, immersed in the background cold and low density disc, are
eventually disrupted. We propose that both planets and the high-T materials in
comets are synthesised inside the GEs. Disruption of GEs separates planets and
small solids as the latter are "frozen-in" into gas and are peeled off together
with it. These small solids are then mixed with the ambient cold disc
containing ices before being incorporated into comets. Several predictions of
this picture may be testable with future observations of the Solar System and
exoplanets.
