  Though efforts to detect them have been made with a variety of methods, no
technique can claim a successful, confirmed detection of a moon outside the
Solar System yet. Moon detection methods are restricted in capability to
detecting moons of masses beyond what formation models would suggest, or they
require surface temperatures exceeding what tidal heating simulations allow. We
expand upon spectroastrometry, a method that makes use of the variation of the
centre of light with wavelength as the result of an unresolved companion, which
has previously been shown to be capable of detecting Earth-analogue moons
around nearby exo-Jupiters, with the aim to place bounds on the types of moons
detectable using this method. We derived a general, analytic expression for the
spectroastrometric signal of a moon in any closed Keplerian orbit, as well as a
new set of estimates on the noise due to photon noise, pointing inaccuracies,
background and instrument noise, and a pixelated detector. This framework was
consequently used to derive bounds on the temperature required for Solar
System-like moons to be observable around super-Jupiters in nearby systems,
with $\epsilon$ Indi Ab as an archetype. We show that such a detection is
possible with the ELT for Solar System-like moons of moderate temperatures
(150-300 K) in line with existing literature on tidal heating, and that the
detection of large (Mars-sized or greater) icy moons of temperatures such as
those observed in our Solar System in the very nearest systems may be feasible.
