  Close-in planets undergo strong tidal interactions with the parent star that
modify their spins and orbits. In the two-body problem, the final stage for
tidal evolution is the synchronisation of the rotation and orbital periods, and
the alignment of the planet spin axis with the normal to the orbit (zero planet
obliquity). The orbital eccentricity is also damped to zero, but over a much
longer timescale, that may exceed the lifetime of the system. For non-zero
eccentricities, the rotation rate can be trapped in spin-orbit resonances that
delay the evolution towards the synchronous state. Here we show that capture in
some spin-orbit resonances may also excite the obliquity to high values rather
than damp it to zero. Depending on the system parameters, obliquities of 60 to
80 degrees can be maintained throughout the entire lifetime of the planet. This
unexpected behaviour is particularly important for Earth-like planets in the
habitable zone of M-dwarf stars, as it may help to sustain temperate
environments and thus more favourable conditions for life.
