Scaling of convection in high-Pressure ice layers of large icy moons and implications for habitability
Authors: Lebec Laëtitia , Labrosse Stéphane , Morison Adrien , Tackley Paul 
Published: March 2021

&lt;p&gt;&lt;span&gt;The existence of a high pressure ice layer between the &lt;/span&gt;&lt;span&gt;silicate &lt;/span&gt;&lt;span&gt;core and the liquid ocean in large icy moons and ocean&lt;/span&gt;&lt;span&gt; worlds&lt;/span&gt; &lt;span&gt;is usually &lt;/span&gt;&lt;span&gt;seen as a barrier &lt;/span&gt;&lt;span&gt;to&lt;/span&gt;&lt;span&gt; habitability, &lt;/span&gt;&lt;span&gt;preventing the compounds needed for life to flow into the ocean&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;More recently,&lt;/span&gt; &lt;span&gt;three studies from Choblet &lt;/span&gt;&lt;span&gt;et al &lt;/span&gt;&lt;span&gt;[1] and &lt;/span&gt;&lt;span&gt; Kalousov&amp;#225; &lt;/span&gt;&lt;span&gt;et al&lt;/span&gt;&lt;span&gt; [2, 3] &lt;/span&gt;&lt;span&gt;challenged&lt;/span&gt;&lt;span&gt; that hypothesis and showed that, &lt;/span&gt;&lt;span&gt;in&lt;/span&gt;&lt;span&gt; certain conditions, exchanges were possible between the core and the ocean, allowing &lt;/span&gt;&lt;span&gt;transport of salts &lt;/span&gt;&lt;span&gt;toward&lt;/span&gt;&lt;span&gt; the ocean. &lt;/span&gt;&lt;span&gt;Here, we consider an effect not taken into account in these previous studies: the possibility of mass exchange between the ice and ocean layers by phase change. Convect&lt;/span&gt;&lt;span&gt;ive stresses in the solid create &lt;/span&gt;&lt;span&gt;a&lt;/span&gt;&lt;span&gt; topography o&lt;/span&gt;&lt;span&gt;f&lt;/span&gt;&lt;span&gt; the interface which can be erased by melting and freezing if flow on the liquid side is efficient. This effect is included in a convection model as a phase change boundary condition, &lt;/span&gt;&lt;span&gt;allowing&lt;/span&gt;&lt;span&gt; a non-zero vertical velocity at the surface of the HP ice layer, which ha&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; a significant impact on the flow dynamics and enable&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; exchanges with the ocean by fusion and crystallization of the ice at the top interface, &lt;/span&gt;&lt;span&gt;even without partial melting in the bulk of the ice layer&lt;/span&gt;&lt;span&gt;. These exchanges are directly linked to the melting capacity of the ice at the interface between the HP ice layer and the core, depending on the Rayleigh number and the &lt;/span&gt;&lt;span&gt;efficiency&lt;/span&gt;&lt;span&gt; of convection. Then, considering this new condition at the interface between the HP ice layer and the liquid ocean, we propose a scaling of the bottom temperature and the vertical velocity. Applied to a specific celestial body, as Ganymede &lt;/span&gt;&lt;span&gt;or Titan&lt;/span&gt;&lt;span&gt;, it would be the first step to conclude about its habitability.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;em&gt;References:&lt;/em&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[1] &lt;/span&gt;&lt;span&gt;G. Choblet, G. Tobie, C. Sotin, K. Kalousov&amp;#225;, O. Grasset (201&lt;/span&gt;&lt;span&gt;7&lt;/span&gt;&lt;span&gt;). Heat transport in the high-pressure ice mantle of large icy moons. Icarus, &lt;/span&gt;&lt;span&gt;&lt;strong&gt;285&lt;/strong&gt;&lt;/span&gt;&lt;span&gt;, 252-262&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[2] &lt;/span&gt;&lt;span&gt;K. Kalousov&amp;#225;, C. Sotin, G. Choblet, G. Tobie, O. Grasset (201&lt;/span&gt;&lt;span&gt;8&lt;/span&gt;&lt;span&gt;). Two-phase convection in Ganymede&amp;#8217;s high-pressure ice layer &amp;#8212; Implications for its geological evolution. Icarus, &lt;/span&gt;&lt;span&gt;&lt;strong&gt;299&lt;/strong&gt;&lt;/span&gt;&lt;span&gt;, 133-147&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;[3] &lt;/span&gt;&lt;span&gt;K.Kalousov&amp;#225;, C. Sotin (2018). Melting in High-Pressure Ice Layers of Large Ocean Worlds&amp;#8212;Implications for Volatiles Transport. Geophys. Res. Lett., &lt;/span&gt;&lt;span&gt;&lt;strong&gt;45&lt;/strong&gt;&lt;/span&gt;&lt;span&gt;, 8096-8103.&lt;/span&gt;&lt;/p&gt;