  With the detection of extrasolar moons (exomoons) on the horizon, it is
important to consider their potential for habitability. If we consider the
circumstellar Habitable Zone (HZ, often described in terms of planet semi-major
axis and orbital eccentricity), we can ask, "How does the HZ for an Earth-like
exomoon differ from the HZ for an Earth-like exoplanet?"
  For the first time, we use 1D latitudinal energy balance modelling to address
this question. The model places an Earth-like exomoon in orbit around a Jupiter
mass planet, which in turn orbits a Sun-like star. The exomoon's surface
temperature is evolved under the action of stellar insolation, atmospheric
cooling, heat diffusion, eclipses and tidal heating. We use this model to carry
out two separate investigations.
  In the first, four test cases are run to investigate in detail the dependence
of the exomoon climate on orbital direction, orbital inclination, and on the
frequency of stellar eclipse by the host planet. We find that lunar orbits
which are retrograde to the planetary orbit exhibit greater climate variations
than prograde orbits, with global mean temperatures around 0.1 K warmer due to
the geometry of eclipses. If eclipses become frequent relative to the
atmospheric thermal inertia timescale, climate oscillations become extremely
small.
  In the second investigation, we carry out an extensive parameter study,
running the model many times to study the habitability of the exomoon in the
4-dimensional space composed of the planet semi-major axis and eccentricity,
and the moon semi-major axis and eccentricity. We find that for zero moon
eccentricity, frequent eclipses allow the moon to remain habitable in regions
of high planet eccentricity, but tidal heating severely constrains habitability
in the limit of high moon eccentricity, making the habitable zone a sensitive
function of moon semi-major axis.
