Linda J. Horn

Infrared Observations of the Saturnian System from Voyager 2

During the passage of Voyager 2 through the Saturn system, infrared spectral and radiometric data were obtained for Saturn, Titan, Enceladus, Tethys, Iapetus, and the rings. Combined Voyager 1 and Voyager 2 observations of temperatures in the upper troposphere of Saturn indicate a seasonal asymmetry between the northern and southern hemispheres, with superposed small-scale meridional gradients. Comparison of high spatial resolution data from the two hemispheres poleward of 60� latitude suggests an approximate symmetry in the small-scale structure, consistent with the extension of a symmetric system of zonal jets into the polar regions. Longitudinal variations of 1 to 2 K are observed. Disk- averaged infrared spectra of Titan show little change over the 9-month interval between Voyager encounters. By combining Voyager 2 temperature measurements with ground-based geometric albedo determinations, phase integrals of 0.91 � 0.13 and 0.89 � 0.09 were derived for Tethys and Enceladus, respectively. The subsolar point temperature of dark material on Iapetus must exceed 110 K. Temperatures (and infrared optical depths) for the A and C rings and for the Cassini division are 69 � 1 K (0.40 � 0.05), 85 � 1 K (0.10 � 0.03), and 85 � 2 K (0.07 � 0.04), respectively.

Infrared observations of the neptunian system.

The infrared interferometer spectrometer on Voyager 2 obtained thermal emission spectra of Neptune with a spectral resolution of 4.3 cm-1. Measurements of reflected solar radiation were also obtained with a broadband radiometer sensitive in the visible and near infrared. Analysis of the strong C2H2 emission feature at 729 cm-1 suggests an acetylene mole fraction in the range between 9 x 10-8 and 9 x 10-7. Vertical temperature profiles were derived between 30 and 1000 millibars at 70� and 42�S and 30�N. Temperature maps of the planet between 80�S and 30�N were obtained for two atmospheric layers, one in the lower stratosphere between 30 and 120 millibars and the other in the troposphere between 300 and 1000 millibars. Zonal mean temperatures obtained from these maps and from latitude scans indicate a relatively warm pole and equator with cooler mid-latitudes. This is qualitatively similar to the behavior found on Uranus even though the obliquities and internal heat fluxes of the two planets are markedly different. Comparison of winds derived from images with the vertical wind shear calculated from the temperature field indicates a general decay of wind speed with height, a phenomenon also observed on the other three giant planets. Strong, wavelike longitudinal thermal structure is found, some of which appears to be associated with the Great Dark Spot. An intense, localizd cold region is seen in the lower stratosphere, which does not appear to be correlated with any visible feature. A preliminary estimate of the effective temperature of the planet yields a value of 59.3 � 1.0 kelvins. Measurements of Triton provide an estimate of the daytime surface temperature of 38+3-4 kelvins.

Temperature and Thermal Emissivity of the Surface of Neptune's Satellite Triton

Analysis of the preliminary results from the Voyager mission to the Neptune system has provided the scientific community with several methods by which the temperature of Neptunes satellite Triton may be determined. If the 37.5 K surface temperature reported by several Voyager investigations is correct, then the photometry reported by the imaging experiment on Voyager requires that Tritons surface have a remarkably low emissivity. Such a low emissivity is not required in order to explain the photometry from the photopolarimeter experiment on Voyager. A low emissivity would be inconsistent with Triton having a rough surface at the ∼100-�m scale as might be expected given the active renewal processes which appear to dominate Tritons surface.

Hermes Global Orbiter: A Discovery Mission in Gestation

The hermes Global Orbiter (HGO) is a Discovery class mission under study, which is investigating the possibility of placing a small spacecraft in highly elliptical polar orbit about mercury. The purpose of the mission is to conduct observations of the planets surface, atmosphere and magnetosphere.

The Hermes/Voyager mission operations concept

Abstract We describe a shared mission operations concept planned for use in support of the Hermes Global Orbiter mission, a proposed Discovery mission to study the planet Mercury. Voyager, a currently flying interplanetary mission, and Hermes are planning to enter into shared mission operations, a relationship which will permit a new low-cost approach to deep space flight operations. Modifications made to the Voyager Mission Operations System plus incremental staffing increases will enable shared mission operations and allow Hermes to avoid the typically high costs associated with development and staffing of a separate mission operations system. We show that shared mission operations will provide reliable and robust operations for both Hermes and Voyager, and will allow Hermes to benefit from the depth of the Voyager experience. This shared mission operations approach is innovative, and will demonstrate a management and operations approach not used before for simultaneous support of scientifically unrelated missions.