Dr. Paul Estrada

December 21, 2006

SETI Institute Principal Investigator

The main objective of my current research is the continued advancement of our understanding of the formation and evolution of giant planet satellite systems.  Recently, in collaboration with Ignacio Mosqueira of the SETI Institute, we have developed two models for the formation of satellites around gas giant planets with the primary difference between them being in how we treat turbulence.  In the one case, turbulence is allowed to decay post planetary accretion so that the satellites (the largest ones) may open gaps in the subnebula halting their inward migration due to the gas tidal torque, and eventually clearing large portions of the gas disk allowing them (as well as smaller objects) to survive.  In the alternative view, strong turbulence acts to remove the giant planet's gaseous disk on a timescale much faster than the satellites form.  Many of my current research topics are aimed at further understanding of the process of satellite formation in gas-rich and gas-poor environments which is a particularly timely endeavor given the ongoing Cassini mision at Saturn which provides valuable clues to distinguish between our alternative models.  Perhaps even more significant, this research is directly applicable to satellite systems that will most certainly be found around the growing reservoir of observed extrasolar giant planets (EGPs) using forthcoming misions such as COROT, Kepler, and Eddington.

The current known reservoir of EGPs may rasie the possibility that (obervational bias notwithstanding) these systems are more the norm as opposed to planetary systems containing terrestrial planets such as our own.  This suggests the interesting possibility that conditions for habitability (and perhaps indigenous life) may be most common for moons orbiting EGPs in their star system's habitable zone.  Using our recently developed models for giant planet satellite formation, we are exploring a statistical characterization of potential satellite systems around EGPs to allow for possible constraints in the observations for upcoming spacecraft missions.  The idea that EGPs migrated to their current positions (a research area that Mosquiera and I also are exploring through numerical models) suggests expansion of the orbits of their satellites due to shrinkage of the giant planet Hill sphere.  Satellites may migrate inwards (due to the gas tidal torque), and inward and /or outward due to tides (for very close-in EGPs).  Thus very important clues as to the place of origin of the EGP at the time of formation may be inferred from the observed radial location of its satellites.

- SETI Institute Explorer, Special Edition 2006