Dr. Paul EstradaCurriculum Vitae:  If planets are a dime a dozen, moons are less than a penny each. There are at least 139 moons in our solar system, and most of these are the property of the gas giant planets beyond Mars. More than just a nice accompaniment to planets, moons may frequently have habitats in which liquid water could ebb and flow – and possibly be home to life. Planetary scientist Paul Estrada investigates how moons around gas giants are formed, an important question since its answer would give us insight into the nature of moons around the myriad gas giant planets we know orbit other stars. The birth of moons around gas giant planets is superficially similar to planetary formation; however, as Estrada points out, there are some very important differences. To begin with, the “environment” (pressure, density, temperature) of satellite birth is different from that of the planets. Perhaps most important, satellite systems are more compact, which means things tend to happen much faster than on the planetary scale. Consider that the giant planet Jupiter takes a dozen years to orbit the Sun, a lumbering pace compared to the days required for its moons to orbit once. As a result, once a moon forms, it has much less time to find a way to “survive.” This is because, just like the planets, there is the problem that the leftover gas which eventually dissipates over time (a time much longer than required to form the moons or planets) will slow down a newly forming satellite, causing it to spiral into its host planet. Clearly, this doesn’t always happen, and Estrada’s research elucidates exactly how such a catastrophic fate can be avoided. The incentive to understand satellite formation is strong, as these small worlds might be the most plentiful locations for life in the universe.
Projects
Formation and Evolution of Giant Planet Satellite Systems
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Compositional Evolution of Saturn's Rings
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We propose to address the problem of the compositional evolution of Saturn's rings subsequent to meteoroid bombardment with the ultimate goal of obtaining a better understanding of the rings' compositional diversity. We will accomplish this goal by (a) improving on our developed and tested dynamical and radiative transfer models (Cuzzi and Estrada 1998), and (b) analyzing and incorporating into our models a generous amount of recently released Cassini UVIS spectral and occultation, VIMS-IR, and 15-color filter ISS data. In this proposal we focus primarily on modeling the compositional and structural evolution of the Cassini division/A ring transition, but given the diversity of the available Cassini data, we will be able to broaden our applications to model the entire A ring. The expected outcome of this proposed work will be a better understanding of the individual constituent materials that make up ring composition, how particle sizes vary across the rings, the presence or absence of short timescale (transient) fine structure features, ring particle phase functions, radially variable values of ring layer packing fractions, and the combined process of structural and compositional evolution. The broad wavelength range covered by the Cassini data set we propose to employ here will make possible the most comprehensive ring compositional study to date.
Accretion Disk Processes
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The main objective of this proposed research is the continued advancement in our understanding of: the growth of dust to planetesimals in both the nebular and subnebular environments; and the formation and evolution of giant planet satellite systems.
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