Would Europa be an ocean planet if it were in the habitable zone? If a Europa-like body were in the Sun's habitable zone, let's say in an orbit between Earth and Mars, would the body become and remain a water ocean planet? In the habitable zone, the Sun would warm up and melt Europa's icy surface which will first turn into water vapor because Europa has no atmosphere, but the water vapor might form an atmosphere around Europa (which would contain oxygen as well) and eventually Europa might get a liquid water surface. Would that be possible? And would the atmosphere remain or couldn't it remain due to Europa's low gravity? But what if the Europa-like body had a Mars-like gravity and/or an Earth-like magnetosphere?
According to Arnscheidt et al. (2019) &quot;Atmospheric Evolution on Low-Gravity Waterworlds&quot;, the transition between &quot;planet-like&quot; and &quot;comet-like&quot; (escaping) atmospheres occurs at a surface gravity of around 1.48 m/s2. As a caveat, the waterworlds being considered in the paper are objects which have water reservoirs of 40% of the total mass, which is a much higher fraction than Mars or Europa, such worlds would be more like scaled versions of Ganymede.
The surface gravity on Europa is 1.315 m/s2, putting it on the comet-like side of the transition. According to this, it seems unlikely that Europa would be able to maintain long-term habitable conditions in the face of atmospheric escape.
Martian gravity is 3.71 m/s2, putting it on the planet-like side of the transition, so a &quot;super-Ganymede&quot; with Mars-like gravity would likely be able to maintain long-lived habitable conditions.
They also note that the high albedo of ice means that deglaciating ice worlds tend to skip the long-lived habitable state entirely, going straight from frozen to runaway greenhouse/atmospheric escape:

The ice-albedo feedback can hamper transitions from snowball states to temperate states: this has
already been demonstrated for terrestrial-mass worlds
(Yang et al. 2017). We can incorporate the ice-albedo
feedback into our model using the simple albedo step
function
$$
A(T_s) = \begin{cases}
\alpha_I &amp; T_s &lt; 273\,\mathrm{K} \\
\alpha_L &amp; T_s \ge 273\,\mathrm{K}
\end{cases}
$$
where $\alpha_I$ is the albedo of the icy (snowball) state, and
$\alpha_L$ is the albedo when there is surface liquid water. Hysteresis plots for different choices of $\alpha_I$ are shown in Figure 5. We observe that a snowball state experiencing
a stellar flux-driven deglaciation generally bypasses the
long-lived state entirely, except for very low $\alpha_I$ values.
Although the mechanism setting the inner edge of the
habitable zone is different, the conclusion of the habitable state likely being bypassed upon stellar flux-driven
deglaciation is the same as that of Yang et al. (2017).

(emphasis mine)