  HATS-8b is a low density transiting super-Neptune discovered as part of the
HATSouth project. The planet orbits its solar-like G dwarf host (V=14.03 $\pm$
0.10 and T$_{eff}$ =5679 $\pm$ 50 K) with a period of 3.5839 d. HATS-8b is the
third lowest mass transiting exoplanet to be discovered from a wide-field
ground based search, and with a mass of 0.138 $\pm$ 0.019 M$_J$ it is
approximately half-way between the masses of Neptune and Saturn. However
HATS-8b has a radius of 0.873 (+0.123,-0.075) R$_J$, resulting in a bulk
density of just 0.259 $\pm$ 0.091 g.cm$^{-3}$. The metallicity of the host star
is super-Solar ([Fe/H]=0.210 $\pm$ 0.080), arguing against the idea that low
density exoplanets form from metal-poor environments. The low density and large
radius of HATS-8b results in an atmospheric scale height of almost 1000 km, and
in addition to this there is an excellent reference star of near equal
magnitude at just 19 arcsecond separation on the sky. These factors make
HATS-8b an exciting target for future atmospheric characterization studies,
particularly for long-slit transmission spectroscopy.
