Hi All

A couple of interesting abstracts from different AGU meetings...

[sorry there's no links, but I got them off NASA's ADS. Haven't found papers online yet]

Both are worth a read. The broad implications are that at least "thin" seams of liquid water (or water/ammonia) surround the rocky cores of the larger icy moons of the outer planets and Pluto. Especially interesting is that even the larger Saturnian & Uranian moons (R ~ 750 km) could have such layers if their radiogenic heating is greater than regular chondritic values (as obtains for the Moon).

I'm not going to say "Life" because such environments are unlikely to be very chemically rich, but such seams provide a means of resurfacing those satellites to the present day and also could be a useful heat-source for later exploitation/colonisation efforts. They could certainly be convenient heat sources for any ETIs who might've parked themselves in the Outer Sol System.

Title: Oceans in ice-rock bodies: conditions for the existence of subsurface liquid water

Authors: Rainey, E. S.; Stevenson, D. J.

Journal: American Geophysical Union, Fall Meeting 2003, abstract #P51B-0447

Abstract Copyright: (c) 2003: American Geophysical Union

Abstract
In an ice-rock body, it is possible for a subsurface ocean to exist as long as there is a sufficient heat source in the rocky core to maintain melting

temperatures in the ice layer. Since the melting point of ice I decreases with pressure, it is only necessary for temperatures to reach ~ 251 K for liquid

water to be present in the ice layer. If ammonia is present, the minimum necessary temperature decreases further, to around 176 K. Heat loss in

differentiated ice-rock bodies occurs primarily through thermal convection in the outer layer of ice, as long as the body is not too small (larger than ~ 200

km radius). To model convection in the ice layer, we used scaling laws for stagnant lid convection with Newtonian rheology (Solomatov, 1995), which relate

heat flux to the internal Rayleigh number of the convecting layer. Newtonian rheology is appropriate for the low stresses under consideration. Since the

viscosity of ice I is strongly temperature-dependent, convection in the ice layer occurs in the stagnant lid regime, which allows for higher temperatures at

depth than constant viscosity convection. For ice-rock bodies with a given size, composition, and heat source, we calculated the interior temperature and

compared it to the ice I solidus to determine whether an ocean could be present. Since both the heat flux at the base of the ice layer and the gravitational

acceleration are proportional to the radius of the body, it is effectively much harder for oceans to exist in small bodies. Using plausible choices of

parameters for pure ice I, it is possible for oceans to exist in bodies as small as ~ 1000 km radius, meaning that candidates for subsurface oceans include

not only the icy Galilean satellites and Titan but also Triton and Pluto. If ammonia is present, oceans can exist in bodies as small as the largest Saturnian

and Uranian moons ( ~ 750 km radius). In all of these cases, whether oceans can be present depends strongly on the rheological parameters of ice I, which are

not well known at planetary conditions. Another important parameter is the radiogenic heating rate of the rock, which may be greater than typical chondritic

values if the rock is undepleted in potassium.

*********************************

Title: Aqueous Seams in the Small Moons of Saturn and Uranus

Authors: England, C.

Journal: American Geophysical Union, Fall Meeting 2002, abstract #P72B-0497

Abstract Copyright: (c) 2002: American Geophysical Union

Abstract

Eight small moons of Saturn and Uranus have a size and mass sufficient to have formed, and possibly maintained, an aqueous seam between a radiogenic rocky

core and an insulating icy mantle. Analysis of thermal conduction in a composite sphere indicates that, at radiogenic rates typical of chondritic meteorites,

four of these moons could maintain thin oceans even without tidal or other uncharacterized internal heating. If the radiogenic rate of rocky outer-planetary

material is characteristic of the returned Lunar samples, which is about double the chondritic rate, aqueous seams may have formed in all eight moons as well

as in Triton and Pluto, and could be maintained to the present day.

Trans-Neptunian Objects with radii greater than 910 km are also candidates for thin oceans, the minimum radius reduced to 720 km if Lunar radiogenic rates

are assumed. The assumption of differentiation of rock and ice in smaller bodies is supported by the high radiogenic rates during the formation of the Solar

System. The melting point of icy materials was easily exceeded, leading to their outward flow and the corresponding concentration of radiogenic material in

the core. Bodies with a density of about 1750 kg/m3 have the best proportion of ice and rock that balances the insulating value of the former with the heat

production of the latter. Lower density bodies with higher water content such as Rhea may be more easily differentiated and therefore more likely to form and

maintain an ocean. The presence of low-viscosity seams can be a major influence on the character and dissipation of tidal energy.

--------------------------------------------------------------------------------