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our assumption (1), because it is very dicult to imagine how the growth
of Ceres, which is much larger than Vesta, might have been slower, taking
also into account that the two objects accreted at approximately the same
heliocentric distance, and we do not expect that Ceres underwent a signif-
icant migration since the time of its accretion (assumption 3). Moreover,
as we will see below, there are good reasons to believe that the melting of
Ceres would be in any case unavoidable, due to the presence of a substantial
amount of long-lived radionuclides in its original composition.
There are not many possible explanations of this paradox, that can be
reconciled with both current understanding of planetesimal growth and the
available observational evidence. A possibility compatible with our assump-
tions (1)-(3) is that in the region of Ceres the original planetesimals were
significantly different in composition with respect to those located in the
region of Vesta. In particular, if the gradient in composition of the solid
material in the protoplanetary dust disk was suciently sharp, the planetes-
imals located in the region of growth of Ceres, at about 2.8 AU, could have
included a substantially higher content of volatiles with respect to the plan-
etesimals that were located in the region of growth of Vesta, around 2.35 AU
from the Sun. If this hypothesis is correct, the amount of volatiles in the
interior of Ceres might have been sucient to eciently dissipate the heat
generated by short-lived radiogenic nuclei. This might be a possible solu-
tion of the paradox. In this scenario, what is needed is mainly a suciently
strong gradient in composition of the protoplanetary disk, which may be
plausible. Of course, in the absence of such kind of mechanism of heat dissi-
pation by volatile elements, it is impossible to eciently cool down a body
like Ceres, which, being twice as large as Vesta, in principle requires longer
times to dissipate its internal heat. Even accepting the presence of volatiles,
however, to be able to produce at the end of the phase of heating dissipation
a body having the properties of Ceres, is in any case not so straightforward.
Of course, we cannot exclude other possibilities to solve the “Ceres-
Vesta” paradox. A first possibility might be that our assumption (2) is
not completely correct. In particular, it has been suggested in the past
that electric induction heating could have been very important during the
early phases of the Solar System history, particularly when the Sun expe-
rienced a T-Tau phase.
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If this is true, bodies located at smaller helio-
centric distances might have been heated up more eciently, and this
might explain why Vesta, and not Ceres, was completely melt. This possible
explanation, however, must face two major objections. First, according to
current knowledge of this phenomenon, the strong solar wind developed
