Dr. Kathy Rages

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

“Active Atmospheres on Uranus and Neptune”

HST–GO–10534.01-A

We propose Snapshot observations of Uranus and Neptune to monitor changes in their atmospheres on time scales of weeks, months, and years. Uranus is rapidly approaching equinox in 2007, with another 4 degrees of latitude becoming visible every year. Recent HST observations during this epoch (including 6818: Hammel, Lockwood, and Rages; 8680: Hammel, Rages, Lockwood, and Marley; 8634: Rages, Hammel, Lockwood, Marley, and McKay; and 10170: Rages, Hammel, Lockwood, and Marley) have revealed strongly wavelength-dependent latitudinal structure and the presence of numerous visible-wavelength cloud features in the northern hemisphere. Long-term ground-based observations (Lockwood and Thompson 1999) show seasonal brightness changes whose origins are notwell understood. Recent near-IR images of Neptune obtained using adaptive optics on the Keck Telesccope together with images from our Cycle 9 Snapshot program (8634) show a general increase in activity at south temperate latitudes as well as the possible development of another Great Dark Spot. Further Snapshot observations of these two dynamic planets will elucidate the nature of long-term changes in their zonal atmospheric bands and clarify the processes of formation, evolution, and dissipation of discrete albedo features.

“Radiative Transfer Modeling of Planetary Atmospheric Structure”

NCC 2–1337

The Hubble Space Telescope (HST) continues to produce spatially resolved images of the outer planets on a more-or-less yearly timescale, and is being joined by ground-based telescopes using adaptive optics to produce comparable (~0.1") spatial resolution in the near-infrared. Data from spacecraft such as Voyager, Galileo, and the various Mars orbiters and landers can still be exploited for very high spatial resolution and scattering geometries much different from any that can be observed from the vicinity of Earth.

This proposal is for work over a three year period to utilize the results of past and ongoing spatially resolved observations of planetary atmospheres to model the vertical structure of scatterers in some of those atmospheres, including latitudinal variations, discrete albedo features, and temporal changes on time scales of months and years. The work will include investigating the properties and vertical distribution of albedo features seen over a 12-year period in Neptune’s atmosphere by both Voyager and HST, examining changes in Uranus’ atmosphere which may be seasonal in origin, characterizing the properties of Jovian and saturnian stratospheric hazes seen by Galileo, Voyager, and HST, and including sunlight scattered by dust in the atmosphere of Mars in the determination of photometric properties for surface objects (rocks).

"Radiative Transfer Modeling of Planetary Atmospheric Structure"

NNA05CS79A

The Hubble Space Telescope (HST) continues to produce spatially resolved images of the outer planets on a more-or-less yearly timescale, and is being joined by ground-based telescopes using adaptive optics to produce comparable (~0.1") spatial resolution in the near-infrared. Data from spacecraft such as Voyager and Galileo can still be exploited for very high spatial resolution and scattering geometries much different from any that can be observed from the vicinity of Earth, and Cassini is just beginning its multi-year mission in orbit around Saturn.

This project proposes, over a three year period, to utilize the results of past and ongoing spatially resolved observations of planetary atmospheres to model the vertical structure of scatterers in some of those atmospheres, including latitudinal variations, discrete albedo features, and temporal changes on time scales of months and years. The work will include investigating the properties and vertical distribution of albedo features seen over a 15-year period in Neptune’s atmosphere by both Voyager and HST, examining changes in Uranus’ atmosphere which may be seasonal in origin, and characterizing the properties of jovian and saturnian stratospheric hazes seen by Cassini, Galileo, Voyager, and HST.