  (Aims) We investigate whether volcanic exomoons can be detected in thermal
wavelength light curves due to their phase variability along their orbit. The
method we use is based on the photometric signal variability that volcanic
features or hotspots would cause in infrared (IR) wavelengths, when they are
inhomogeneously distributed on the surface of a tidally heated exomoon (THEM).
(Methods) We simulated satellites of various sizes around an isolated planet
and modeled the system's variability in two IR wavelengths, taking into account
photon shot noise. The moon's periodic signal as it orbits the planet
introduces a peak in the frequency space of the system's time-variable flux. We
investigated the THEM and system properties that would make a moon stand out in
the frequency space of its host's variable flux. (Results) The moon's signal
can produce a prominent feature in its host's flux periodogram at shorter IR
wavelengths for hotspots with temperatures similar to the ones seen on the
Jovian moon, Io, while the same moon would not be identifiable in longer IR
wavelengths. By comparing observations at two different wavelengths, we are
able to disentangle an exomoon's signal from the planet's one in the frequency
domain for system distances up to $\sim$10 pc for Mars-sized exomoons and even
further for Earth-sized ones for transiting and non-transiting orbital
inclinations. (Conclusions) This method enlarges the parameter space of
detectable exomoons around isolated planetary mass objects and directly imaged
exoplanets, as it is sensitive to Io-Earth sized exomoons with hot volcanic
features for a wide range of non-transiting orbital inclinations. Exomoon
transits and the detection of outgassed volcanic molecules can subsequently
confirm a putative detection.
