Prof. Patrick Irwin

Abstract:

Saturn's poles exhibit an unexpected symmetry in hot, cyclonic polar vortices, despite huge seasonal differences in solar flux. The cores of both vortices are depleted in phosphine gas, probably resulting from subsidence of air into the troposphere. The warm cores are present throughout the upper troposphere and stratosphere at both poles. The thermal structure associated with the marked hexagonal polar jet at 77 degrees N has been observed for the first time. Both the warm cyclonic belt at 79 degrees N and the cold anticyclonic zone at 75 degrees N exhibit the hexagonal structure.

Abstract:

This Letter reports on a search for infrared emissions of isotopologues of CO2 in the atmosphere of Titan using spectral data recorded by the Cassini Composite Infrared Spectrometer (CIRS). We have made a successful 6.5 σ detection of ¹³CO2 at a fraction CO 2/¹³CO2 = 84 ± 17, consistent with measurements of ¹²C/¹³C in other species, and also the terrestrial value (89). We also And a probable 3.5 σ detection of C ¹⁶O¹⁸O at a fraction CO2/ C¹⁶O ¹⁸O = 173 ± 55, slightly lower than the terrestrial value (253) and consistent with the twofold enhancement in ¹⁸O reported previously in CO, or with an intermediate value as suggested by chemistry. These isotopic ratios provide important constraints on models of the formation, evolution, and current processes in Titan's atmosphere. © 2008, The American Astronomical Society, All rights reserved.

Abstract:

This Letter reports the first detection of the three ¹³C isotopologues of HC3N on Titan, from Cassini Composite Infrared Spectrometer (CIRS) infrared spectra. The data are limb spectra taken at latitudes N54°-N69° in 2006 and 2007 when HC3N was enhanced in the north. Using a new line list for the vs bands of all isotopologues, we have modeled the isolated emission of H¹³CCCN at 658.7 cm^-1 and both HC¹³CCN and HCC¹³CN at 663.0 cm^-1, which are blended with the Q-branch of HC3N at 663.3 cm^-1 at the resolution of CIRS (0.5 cm^-1) and detectable as an increase in the intensity of the low-frequency wing. Using the resolved pair H¹³CCCN /HC3N we find ¹²C/ ¹³C = 79 ± 17, in line with other measurements on Titan from Cassini and Huygens. © 2008, The American Astronomical Society, All rights reserved.