That paper actually raises a point to bear in mind when figuring out how to render these planets.
Quote:
Using the H2O-REOS equation of state for water (French et al. 2009; Nettelmann et al. 2010) and thermal evolution models of Lopez & Fortney (2014), we find that even at an age of 8 Gyr the temperature at the bottom of such an envelope will be ≳1400K and the pressure will reach ≈130 kbar. For comparison, the pressure in the deepest parts of Earth’s oceans is ≈1 kbar. Moreover, these calculations don’t include the possibility of significant tidal heating from planet-planet interactions, which could raise the interior temperature even higher. At such a high pressure and temperature, water will be far beyond the triple point and far too hot for high pressure ices like ice VII and X. Instead, it will exist as a high pressure molecular fluid, much like the deep interiors of Neptune and Uranus (Fortney et al. 2011; Nettelmann et al. 2011). Therefore, liquid water will likely only exist in clouds near the top of TRAPPIST-1f’s atmosphere and our results suggest that it is no more likely to be habitable than any other gas or ice-giant with water clouds in its atmosphere.
This makes me wonder if it is worth implementing special handling for planets between the 100% rock and 100% ice compositions, or just to throw everything larger than the maximum rocky planet size into the gas giant category: this suggests that only very small ice planets (smaller than most known exoplanets) will be ocean worlds.
Furthermore, the most recent update (
Wang et al., 2017) seems to have substantially decreased the masses for the planets, with only planets c and d having their estimates within the rocky planet region. Given that the planets seem to be in near-resonances and therefore likely migrated inwards from colder parts of the system, ice-rich compositions don't seem too implausible.
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