Dr. Kathy Rages
Curriculum Vitae:  Astronomer Kathy Rages studies outer planet atmospheres, particularly those of Uranus and Neptune—two planets that are very similar. Except when they’re not. These two denizens of the deep solar system are similar to one another in size, and both have a rocky core, an icy mantle, and an atmosphere of hydrogen and helium. But Uranus, in visible light, resembles a featureless cue ball. Neptune, on the other hand, sports a dynamic atmosphere characterized by prominent features such as the Voyager-era Great Dark Spot and its Bright Companion (now long gone, but replaced by other easily visible features). Why the difference? Perhaps it has something to do with Uranus’s extreme axial tilt. Or maybe it’s because of the other big difference between the two planets: the fact that Uranus doesn’t seem to have any significant internal heat source, while Neptune generates almost three times as much heat internally as it gets from the Sun. Two decades have passed since Voyager last examined Uranus up-close. This year will be an equinox for this world, when the Sun will be directly over the equator. After decades of darkness, Kathy is expecting increased activity in Uranus’s atmosphere, and the long-lost answers to why it seems so unlike its outer-planet sibling.
Projects
Investigating Near-Equinox Atmospheric Change on Uranus
HST-GO-11118.03A
This work consists of photometric calibration of images of Uranus obtained with multiple filters on the Wide Field./Planetary Camera2 of the Hubble Space Telescope, measurement of specific intensities (I/F) and determination of scattering geometry for latitude bands in the range -40-60 degrees in both the northern and southern hemispheres, production of center-to-limb( CTL) intensity profiles for all latitude bands in each filter of interest, and comparison of these CTL profiles with radiative transfer calculations to derive properties of scatterers and absorbers in the top few optical depths of Uranus' atmosphere at latitudes covered by a bright polar cap and polar collar in the southern hemisphere, but not (so far) in the northern hemisphere. A northern polar cap is expected to form at some point during Uranus' seasonal cycle, and determining when, how, and how rapidly this occurs will supply significant constraints on models of uranian atmospheric dynamics.
Monitoring Active Atmospheres on Uranus and Neptune
HST-GO-11156.01A
Photometric calibration of images of Uranus and Neptune obtained with seven different filters on the Wide Field/Planetary Camera 2 on the Hubble Space Telescope. Measurement and specific intensities and determination of scattering geometry for selected latitude bands on each planet, development of center-to-limb (CTL) profiles for them, and comparison of these CTL profiles of specific intensity (I/F) with radiative transfer calculations to derive the time-varying properties of scatterers and absorbers in the top few optical depths of both planets' atmospheres. Discrete albedo features will also be identified and their movements possibly tracked, depending on the interval between visits.
Seasonal Changes on Uranus: Analysis of Imaging Data
NNX07AF25G
Uranus is in the midst of a unique era from an observational perspective: the planet's northern hemisphere has come into view for the first time in decades and is now revealing a surprising array of tantalizing detail, while regions of the southern hemisphere also display levels of activity never previously observed with modern detectors. Uranus as a whole has changed noticeably since Voyager was there in 1986, darkening since 1988 after brightening steadily from1972 to 1985. Hubble Space Telescope (HST) observations since 1994 show changes in the banded structure of Uranus' bright south polar cap. Keck observations using adaptive optics (AO) have recorded unprecedented levels of activity near the southern polar collar. A tremendous amount of data has been obtained over the past few years, and preliminary analyses of the individual data sets has started. The recent Uranus data include: images from the HST Wide-Field Planetary Camera 2 (WFPC2), Advanced Camera for Surveys (ACS), and Near Infrared Camera/Multi-Object Spectrometer (NICMOS); near-infrared images from Keck Observatory using AO to obtain spatial resolution comparable to or better than HST; and SpeX infrared spectra obtained at the Infra-Red Telescope Facility (IRTF) on Mauna Kea. We propose here a coordinated analysis of these diverse sets of Uranus observations and the original Voyager data set to investigate the nature of long-term (seasonal) changes on Uranus over the past 20 years. We will model the full time span of Uranus observations since the Voyager era to seek out significant temporal changes in such parameters as (1) the methane cloud's altitude, optical thickness, and single scattering albedo; (2) aerosol absorption below the base ofthe methane cloud; and (3) the height of the putative H2S cloud at >-3 bars. We will address a number of questions regarding the Uranian atmosphere. How do the northern and southern hemispheres differ in vertical aerosol structure? Is Uranus' southern hemispheric haze abundance varying? Is the asymmetry of the planet's atmosphere time-variable? (Models suggest that significant changes in the radiation balance of the atmosphere occur on seasonal cycles; the north-south dichotomy could be a detectable manifestation of such changes.)
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