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Project Progress

Progress was made concerning the origin and nature of the earliest terrestrial atmospheres, specifically with regards to the heavy bombardment period of the early solar system. Mischna and Newman showed that large impacts (up to perhaps 100x the K/T impactor in mass) may contribute to a planet’s volatile reservoir, thus serving as a source for early atmospheres, as long as the planet is sufficiently large (~Earth-sized). For Mars-sized planets, it is difficult to retain a substantial atmosphere through impact accretion. The culmination of this work has been the submission of a manuscript detailing the numerical and analytic calculations. In the upcoming year, Mischna and Newman hope to extend this work to include statistical simulations of the impact conditions of the inner solar system both during the heavy bombardment and in subsequent time.

Significant progress has been made on the theoretical basis for tidally heated habitable zones in general, and in Europa in particular during this past year. A new methodology for solving the coupled orbital and rotational dynamics of rigid bodies was developed by Varadi, Musotto Moore, and Schubert and was submitted for publication (Varadi et al., 2003). A study of the orbital evolution of the Galilean satellites was also published (Musotto et al., 2002), in which the influence of Jupiter’s oblateness on the shape of the satellites’ orbits was shown to be quite significant, especially in the case of Io. The extension of this theory to deformable bodies is underway. The development of a semi analytical technique for studying the stability of orbits in the three body problem was developed in collaboration with Nader Haghighipour of the Carnegie Institute (Haghighipour et al., 2003).

The thermal evolution of tidally heated bodies is the critical link between tidal heating and habitability, and Io, though not very biologically promising, provides important constraints on the dynamics of such bodies. The nature of Io’s thermal equilibrium was studied in a paper by Moore (Moore, 2003), where it was demonstrated that Io’s heat is probably transported by melt segregation rather than thermal convection.

Progress was made this year on studies of the likelihood for subsurface liquid water oceans within the icy Galilean satellites. The work of Spohn and Schubert suggests that a liquid water ocean is likely to exist on Europa beneath a few tens of kilometers of ice even in the absence of tidal heating. A liquid water ocean beneath about a hundred kilometers of ice is also plausible for Ganymede and perhaps Callisto. The effects of possible subsurface oceans on the tidal dynamics of Ganymede and Callisto were studied by Moore and Schubert.

We also studied the conditions under which pore water in carbonaceous chondrite parent bodies would have undergone thermal convection in the protoplanetary phase of Solar System history (Young et al., 2003). The goal was to constrain the volumes of water that were contained in the building blocks of rocky planets; estimates of water volume in asteroidal bodies represented by meteorites depend critically on whether or not the water moved. The main parameters controlling whether or not pore water undergoes convection are the concentration of primordial heat sources and the permeability and size of the bodies. Pore water convection is expected to occur in bodies larger than several tens of kilometers in radius.