  The nature and origin of the asteroids orbiting in near-Earth space,
including those on a potentially hazardous trajectory, is of both scientific
interest and practical importance. We aim here at determining the taxonomy of a
large sample of near-Earth (NEA) and Mars-crosser (MC) asteroids and analyze
the distribution of these classes with orbit. We use this distribution to
identify their source regions and to study the strength of planetary encounters
to refresh asteroid surfaces. We measure the photometry of these asteroids over
four filters at visible wavelengths on images taken by the SDSS. These colors
are used to classify the asteroids into a taxonomy consistent with the widely
used Bus-DeMeo taxonomy based on spectroscopy. We report here on the taxonomic
classification of 206 NEAs and 776 MCs determined from SDSS photometry,
representing an increase of 40% and 663% of known taxonomy classifications in
these populations. Using the source region mapper by Greenstreet et al. (2012),
we compare the taxonomic distribution among NEAs and main-belt asteroids of
similar diameters. Both distributions agree at the few percent level for the
inner part of the Main Belt and we confirm this region as a main source of
near-Earth objects. The effect of planetary encounters on asteroid surfaces are
also studied by developing a simple model of forces acting on a surface grain
during planetary encounter, which provides the minimum distance at which a
close approach should occur to trigger resurfacing events. By integrating
numerically the orbit of the 519 S-type and 46 Q-type asteroids back in time
and monitoring their encounter distance with planets, we seek to understand the
conditions for resurfacing events. The population of Q-type is found to present
statistically more encounters with Venus and the Earth than S-types, although
both types present the same amount of encounters with Mars.
