The planet crossing asteroids in the inner solar system have strongly
chaotic orbits and the distributions of their angular elements are
often regarded as uniform random. We quantified the level of intrinsic
non-uniformities of the angular elements for the dynamical subgroups
of Near Earth Objects (NEOs) and Mars Crossing Objects (MCOs). Using
the methods of angular statistics, we found several statistically
significant departures from uniform random angular distributions.
These non-uniform distributions of the angular elements may affect the
asteroidal impact fluxes on the planets. We developed a new approach
that accounts for the non-uniform angular elements of planet crossing
asteroids to investigate the impact flux and its seasonal variation on
the Earth, the Moon, and Mars.
The impact flux of NEOs on the Earth-Moon system is found to be not
affected significantly by the non-uniform distribution of angular
elements of NEOs. The impact flux on Mars, however, is found to be
reduced by a factor of about 2 compared to the flux that would obtain
from the assumption of uniform random distributions of the angular
elements of MCOs. Moreover, the impact flux on Mars has a strong
seasonal variation, with a peak when the planet is near aphelion. We
found that the amplitude of this seasonal variation is a factor of 4-5
times smaller compared to what would be obtained with a uniform random
distribution of the angular elements of MCOs. We calculate that the
aphelion impact flux on Mars is about three times larger than its
perihelion impact flux.
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