Professor Len Tyler
STAR lab. Stanford University
Major scientific questions regarding the Pluto-Charon system include the fundamental physical parameters of the system, the degree of internal differentiation of the two bodies, the geology, geophysics, composition, and age of the surfaces of Pluto and Charon, the nature of the atmosphere and its escape rate, the nature of the interaction of the system with the solar wind, and details of the apparent unique exchange of material between Pluto and Charon.
A group within STARLab is responsible for design and implementation of a radio experiment (REX) employing uplink radio occultation to determine conditions at the base of the atmosphere, where it is expected that temperature is in the high 30s kelvin, and the atmospheric pressure is in the range of 3-50 x 10^(-6) that of Earth. While challenging, this measurement is feasible and will also yield the atmospheric structure to an altitude of roughly 30 km. Anticipated effects by the atmosphere on the radio are signal are extremely small, necessitating the use of high-power, ground-based signal sources with reception on the NH-PKB spacecraft in order to achieve the required SNR. Stanford will design and provide the necessary signal processing functions needed to implement the on-board reception of the uplink signal. By-products of the atmospheric experiment capabilities are accurate determinations of the individual masses of Pluto and Charon, the ionospheric structure (if is exists at densities greater than about 1000-2000/cc), and the thermal emission temperatures of surfaces of Pluto and Charon. A bistatic scattering observation of the surface of Pluto is under consideration.
Congress mandated in the FY02 budget bill that NASA select a PKB team from five proposals submitted in the spring of 2001, and provided incremental funding for the detailed design. The Bush Administration and the new NASA Administrator, Sean O'Keefe, formerly of OMB, strongly oppose the NH-PKB mission. Substantial sums are needed in FY03 to continue the development and meet an '06 launch date, and this will be the subject of debate as the year advances. There are good reasons for visiting Pluto-Charon now, before the system moves much farther from the sun, with the result that freezing of the atmosphere halts several important processes for the next two centuries, and frost obscures the surfaces of Pluto-Charon.