  We propose a measure, the joint differential entropy of eigencolours, for
determining the spatial complexity of exoplanets using only spatially
unresolved light curve data. The measure can be used to search for habitable
planets, based on the premise of a potential association between life and
exoplanet complexity. We present an analysis using disk-integrated light curves
from Earth, developed in previous studies, as a proxy for exoplanet data. We
show that this quantity is distinct from previous measures of exoplanet
complexity due to its sensitivity to spatial information that is masked by
features with large mutual information between wavelengths, such as cloud
cover. The measure has a natural upper limit and appears to avoid a strong bias
toward specific planetary features. This makes it a candidate for being used as
a generalisable measure of exoplanet habitability, since it is agnostic
regarding the form that life could take.
