RESEARCH IN PLANETARY SCIENCE

Todd Clancy's research is in the area of planetary atmospheres. He uses a variety of observational techniques to probe the climate and chemistry of the terrestrial, Martian, and Venusian atmospheres. These techniques include radio telescopes in New Mexico, Arizona, and Hawaii, as well as imaging and spectroscopic instruments onboard the Hubble Space Telescope and the Mars Global Surveyor spacecraft. Studies of Mars in particular occupy much of his current time and will continue to do so given NASA's long-term plans for Mars exploration into the next millennium. Todd is also involved in the development of the MarsQuest museum exhibit under development at SSI.

With Mike Wolff and Todd Clancy, Barbara Whitney is creating model images of Mars that can be used to learn more about Martian dust properties and ozone abundance. She also calculates the brightness levels of extrasolar planets, and predicts whether their brightness variations can be detected as they orbit their parent star. In addition to planetary work, Barbara applies her light propagation studies to astrophysics.

Mike Wolff's work in Planetary Science is focussed on remote sensing observations of the Martian atmosphere. Working with the group led by Phil James (University of Toledo), Mike uses Hubble Space Telescope images and spectra to characterize the abundance of dust and water ice aerosols, as well as that of ozone, on Mars. Current projects include the study of dust/ice particle sizes and shapes using Mars Global Surveyor (MGS) Thermal Emission Spectrometer data, and of three-dimensional radiative transfer effects in the analysis of MGS and Pathfinder data (both projects in collaboration with Todd Clancy and Barbara Whitney).

Bill Farrand has a NASA Mars Data Analysis Program grant for "Multispectral Mapping of the Martian Polar Regions". He is working on this project with Anne Nolin of the University of Colorado National Snow and Ice Data Center. Bill and Anne are merging the blue and red bands from the Mars Orbiter Camera (MOC) Wide Angle camera with 1.0 micrometer reflectivity data from the Mars Orbiter Laser Altimeter (MOLA) to produce a virtual three band multispectral data set. They are using this data with spectral mixture analysis to determine the fractions of components (ice, dust, and frost) in the polar regions. Bill is also working with Jim Bell of Cornell University and Jeff Johnson of the USGS on the "Sub-pixel detectability of materials at the Pathfinder landing site." This work involves using multispectral data from the Imager for Mars Pathfinder (IMP) and applying advanced image processing techniques to search for previously unobserved materials and to better constrain the identity and origin processes of previously detected surface materials at the Mars Pathfinder landing site.

Heidi Hammel specializes in the atmospheres of the outer planets and their satellites. Her latest research focuses on imaging of Uranus and Neptune with the Hubble Space Telescope (HST) and the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. She is also involved in research efforts related to extrasolar planets.

Heidi is conducting a study of Neptune's largest moon, Triton, which has recently been found to be undergoing global warming. An increase in temperature may have occurred in the atmosphere of Triton during the last eight years, judging from results of recent occultations of this satellite of Neptune. The atmosphere is thought to be in vapor pressure equilibrium with the surface frosts; hence changes in frost coverage can have significant implications for atmospheric stability. Heidi has a set of multiwavelength Triton data spanning more than a decade. (The data were taken for Neptune, but Triton is visible in most of the images.) She is completing a comprehensive and self-consistent analysis of the complete Triton data set. These frost data will provide constraints for models which are being invoked to explain the occultation results.

Working with Kathy Rages of NASA Ames Research Center, Heidi is investigating the vertical structure of visible light scatterers in the atmosphere of Neptune. They are combining Voyager images with recent and anticipated HST images to explore the changing scattering properties of zonal bands and discrete spots during the twelve years since the Voyager encounter. They are calculating the reflectivities (I/F values) expected for the observed scattering geometries from an ensemble of physically realistic models of Neptune's atmosphere. By comparing model results with observed reflectivities at various latitudes on Neptune over the past decade, they will determine how the altitudes and optical thicknesses of the major scattering layers are changing. Heidi is examining the discrete features seen to develop and disappear on Neptune during the past decade to determine how they differed from their surroundings at various times in their life cycles. Such features affect Neptune's long-term average bolometric albedo; better characterization of their properties will permit refined estimates of the planet's overall heat balance.

Heidi (with collaborators Wes Lockwood of Lowel Observatory, Kathy Rages of NASA Ames Research Center, and Mark Marley of New Mexico State University) is also exploring the atmosphere of Uranus as the planet plunges toward equinox in 2007. Recent HST images during this unique epoch have revealed: (i) strongly wavelength-dependent latitudinal structure, (ii) the presence of numerous visible wavelength cloud features in the northern hemisphere, (iii) zonal winds which may deviate from the smooth profile implied by the Voyager observations in 1986, and (iv) in the near-IR, discrete features northward of +25 degrees that have the highest contrast ever seen for a Uranian cloud. Specific scientific issues Heidi is addressing with the new HST and ground-based observations are: whether the northern features are indicative of intrinsic change or result simply from a change of viewing angle; the shape and stability of the zonal wind profile; and the source of the as-yet unexplained variations of the atmospheric reflectivity. This period approaching equinox is the first opportunity (in the era of modern instrumentation) to examine the far regions of the northern hemisphere on Uranus.