The Tropospheres of Uranus and Neptune as seen at Microwave Wavelengths

Details The Tropospheres of Uranus and Neptune as seen at Microwave Wavelengths The Tropospheres of Uranus and Neptune as seen at Microwave Wavelengths

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.5004h&link_type=abstract

American Astronomical Society, DPS meeting #40, #50.04; Bulletin of the American Astronomical Society, Vol. 40, p.488

Astronomy and Astrophysics

Astronomy

Scientific paper

Brightness patterns seen at centimeter wavelengths are used to study the deep tropospheres of Uranus and Neptune (pressures from 1 to 50 bars). Early examples are Briggs and Andrew 1980 for Uranus (Icarus 41, 269-277) and Hofstadter et al. 1993 for Neptune (BAAS 25, 1077). We recently collected high-resolution Neptune data with the VLA at 1.3 and 2 cm under excellent conditions, allowing us to make a better comparison of the two ice-giants. As was known, the planets are grossly similar. The polar regions are the brightest (by tens of Kelvin, 20% brighter than the disk average), and both planets have less prominent, bright, mid-latitude bands. We can now say with confidence that Neptune's polar brightening covers a much smaller area than Uranus’ (at least in the south---Neptune's far north is not currently visible). Neptune's bright spot extends from -90 to about -75 degrees latitude, while Uranus’ extends down to -45 degrees at all times of the year. This, combined with Neptune's atmosphere being more opaque than Uranus', supports the idea that Neptune's deep troposphere is more convectively active. Convection brings absorbers (H2O, NH3, H2S) up to high altitudes, making some regions appear dim. Cloud formation in rising air depletes absorbers, changing the vertical opacity structure and making regions of subsidence absorber-free and bright. On Neptune, convective activity extends further towards the poles than it does on Uranus. We will discuss our results in light of recent observations of both planets at shorter wavelengths, and will present a re-analysis of older Neptune data in a search for temporal variability. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. We acknowledge the support of NASA's Planetary Astronomy program, and of the VLA observatory.

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