Leslie A. Young — Page 3

arXiv2007

New Horizons: Anticipated Scientific Investigations at the Pluto System

The New Horizons spacecraft will achieve a wide range of measurement objectives at the Pluto system, including color and panchromatic maps, 1.25-2.50 micron spectral images for studying surface compositions, and measurements of Pluto's atmosphere (temperatures, composition, hazes, and the escape rate). Additional measurement objectives include topography, surface temperatures, and the solar wind interaction. The fulfillment of these measurement objectives will broaden our understanding of the Pluto system, such as the origin of the Pluto system, the processes operating on the surface, the volatile transport cycle, and the energetics and chemistry of the atmosphere. The mission, payload, and strawman observing sequences have been designed to acheive the NASA-specified measurement objectives and maximize the science return. The planned observations at the Pluto system will extend our knowledge of other objects formed by giant impact (such as the Earth-moon), other objects formed in the outer solar system (such as comets and other icy dwarf planets), other bodies with surfaces in vapor-pressure equilibrium (such as Triton and Mars), and other bodies with N2:CH4 atmospheres (such as Titan, Triton, and the early Earth).

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arXiv1997

Stellar Occultation Observations of Saturn's North-Polar Temperature Structure

We have observed a stellar occultation of GSC5249-01240 by Saturn's north polar region on November 20, 1995 from NASA's Infrared Telescope Facility (IRTF). This is the first recorded occultation by the polar region of a giant planet. The occulted region extends 88 km in vertical height and 660 km in horizontal length, over a region from 82.5 to 85 degrees in planetocentric latitude and from 20 to 30 degrees in planetocentric longitude. Based on isothermal model fits to the light curve, we find an equivalent temperature of 130 \pm 10 K at a pressure level of 1.6 \pm 0.1 \mubar, which corresponds to a half-light latitude of 83.2 \pm 0.2 degrees and longitude of 24.1 \pm 0.5 degrees. Using numerical inversion procedures, we have retrieved the temperature profile of the occulted region, which suggests an increase in temperature (with radius) of 14.5 K between 6 and 10 \mubar. We also find temperature fluctuations of 1 to 5 K along the path probed by the occultation; if the observed temperature gradients of these fluctuations apply to the vertical direction only, then this region is super-adiabatic. More likely these thermal gradients are due to a combination of diffractive scintillations and horizontal temperature variations. Given that isothermal model fits and numerical inversions cannot separate individual contributions to observed temperature fluctuations, such as from vertical variations, horizontal variations, and scintillations, this occultation requires a further study.

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