High-Precision Measurements of Planetary Rotation

In this project, high-precision rotation measurements of Europa, Ganymede, and Venus will be acquired and interpreted to make advances in icy shell geology, geophysics, and astrobiology. The technique is Earth-based radar speckle tracking, in which radio waves are emitted by large transmitters towards these Solar System bodies and the radar echoes are recorded with our largest radio telescopes. This project trains a graduate student in observational astronomy. It also develops a module (teacher resource and student worksheet) that engages students in grades 3–5 about planetary astronomy, recognized as a gateway into the STEM fields (Science, Technology, Engineering, and Mathematics). This activity is expected to awaken or nurture a passion for STEM in young kids and set a fraction of them on a course towards a career in STEM. The rotational response of planetary bodies to a variety of forcings provides fundamental insights into their interior structure and rheology, their dynamical and thermal evolution, and core-mantle or shell-ocean interactions. This investigation will test models of the origin of Europa’s surface features, whether its ice shell is decoupled from its interior, and determine the rheology and moment of inertia of the shell. For Ganymede and Venus, this project seeks to determine their interior structure and provide insights into their dynamical, thermal, and magnetic field evolutions. Previous results from the radar speckle tracking observations have been confirmed at the 1% level by spacecraft observations. Project objectives are: (1) To confirm and improve the first measurements of the spin axis orientations of Europa and Ganymede, yielding obliquities with 10% precision; (2) To measure or place upper bounds on the amplitude of longitude librations of Europa; (3) To measure the orientation of the spin axis of Venus with 2” precision, the spin precession rate, and the polar moment of inertia with 4% uncertainties. The project trains a graduate student in the techniques of observational astronomy – how to write proposals, operate a radio telescope, process radar signals, write manuscripts, and present at conferences – thus contributing to renewal of the workforce. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.