Planetary descent probes: polarization nephelometer and hydrogen ortho/para instruments

While much has been gleaned about the details of the atmospheres of the giant planets, Venus and Titan via remote sensing, it will never replace the direct reality of an in situ instrument. There remain many questions about the structure and dynamics of the other planetary atmospheres in our solar system that need to be addressed by in situ instrumentation, and thus the development of a new breed of descent probe instruments in well warranted. We are developing two instruments that would be excellent additions to the payloads of planetary atmosphere descent probes into the Giant planets, Venus, or Titan. Our first instrument, a polarization nephelometer, uses polarization modulation to determine the intensity and polarization ratio phase functions of ambient aerosols. Measuring both of these phase functions allows much more discriminating conclusions to be drawn about the molecular composition and microphysical parameters of the aerosols. Atmospheric aerosols are key determinants of the global heat balances and atmospheric circulations on all of the above planets. They are as yet still poorly understood. There is a distinct need for polarization nephelometers on descent probes into these planetary atmospheres. Our second instrument, a hydrogen ortho/para instrument, uses acoustic techniques to measure the vertical distribution of this thermodynamically important quantity on the giant planets. The hydrogen ortho/para fraction influences the dynamics of these planet's atmospheres, as well as acting as a tracer of these motions.