  An asymmetry between the ingress and egress times was observed in the near-UV
light curve of the transit planet WASP-12b. Such asymmetry led us to suggest
that the early ingress in the UV light curve of WASP-12b, compared to the
optical observations, is caused by a shock around the planet, and that shocks
should be a common feature in transiting systems. Here, we classify all the
transiting systems known to date according to their potential for producing
shocks that could cause observable light curve asymmetries. We found that 36/92
of known transiting systems would lie above a reasonable detection threshold
and that the most promising candidates to present shocks are: WASP-19b,
WASP-4b, WASP-18b, CoRoT-7b, HAT-P-7b, CoRoT-1b, TrES-3, and WASP-5b. For
prograde planets orbiting outside the co-rotation radius of fast rotating
stars, the shock position, instead of being ahead of the planetary motion as in
WASP-12b, trails the planet. In this case, we predict that the light curve of
the planet should present a late-egress asymmetry. We show that CoRoT-11b is a
potential candidate to host such a behind shock and show a late egress. If
observed, these asymmetries can provide constraints on planetary magnetic
fields. For instance, for a planet that has a magnetic field intensity similar
to Jupiter's field (~ 14 G) orbiting a star whose magnetic field is between 1
and 100G, the stand-off distance between the shock and the planet, which we
take to be the size of the planet's magnetosphere, ranges from 1 to 40
planetary radii.
