  Recently, the Kepler spacecraft has detected a sizable aggregate of objects,
characterized by giant-planet-like radii and modest levels of stellar
irradiation. With the exception of a handful of objects, the physical nature,
and specifically the average densities, of these bodies remain unknown. Here,
we propose that the detected giant planet radii may partially belong to planets
somewhat less massive than Uranus and Neptune. Accordingly, in this work, we
seek to identify a physically sound upper limit to planetary radii at low
masses and moderate equilibrium temperatures. As a guiding example, we analyze
the interior structure of the Neptune-mass planet Kepler-30d and show that it
is acutely deficient in heavy elements, especially compared with its solar
system counterparts. Subsequently, we perform numerical simulations of
planetary thermal evolution and in agreement with previous studies, show that
generally, 10 - 20 Earth mass, multi-billion year old planets, composed of high
density cores and extended H/He envelopes can have radii that firmly reside in
the giant planet range. We subject our results to stability criteria based on
extreme ultraviolet radiation, as well as Roche-lobe overflow driven mass-loss
and construct mass-radius relationships for the considered objects. We conclude
by discussing observational avenues that may be used to confirm or repudiate
the existence of putative low mass, gas-dominated planets.
