  The difference between the measured atmospheric abundances of neon, argon,
krypton and xenon for Venus, the Earth and Mars is striking. Because these
abundances drop by at least two orders of magnitude as one moves outward from
Venus to Mars, the study of the origin of this discrepancy is a key issue that
must be explained if we are to fully understand the different delivery
mechanisms of the volatiles accreted by the terrestrial planets. In this work,
we aim to investigate whether it is possible to quantitatively explain the
variation of the heavy noble gas abundances measured on Venus, the Earth and
Mars, assuming that cometary bombardment was the main delivery mechanism of
these noble gases to the terrestrial planets. To do so, we use recent dynamical
simulations that allow the study of the impact fluxes of comets upon the
terrestrial planets during the course of their formation and evolution.
Assuming that the mass of noble gases delivered by comets is proportional to
rate at which they collide with the terrestrial planets, we show that the
krypton and xenon abundances in Venus and the Earth can be explained in a
manner consistent with the hypothesis of cometary bombardment. In order to
explain the krypton and xenon abundance differences between the Earth and Mars,
we need to invoke the presence of large amounts of CO2-dominated clathrates in
the Martian soil that would have efficiently sequestered these noble gases.
