Aerosol vertical structure in earth-analog atmospheres: Titan's haze and Martian dust

The results from ground- and space-based observations aimed at exploring the aerosol vertical structure in the lower atmosphere of Titan, the methane abundance in Titan's troposphere, and the dust abundance in the martian atmosphere are presented. Investigating the vertical distribution of Titan's lower atmospheric haze and tropospheric methane, as well as martian atmospheric dust, provides insight into dynamical, radiative, and thermal properties of both atmospheres. Titan's lower atmospheric haze profile indirectly provides evidence for atmospheric circulation and condensation processes (i.e., methane rain and clouds). Similarly, suspended martian dust heats up the atmosphere, thus driving the thermal structure.

For the Titan portion of this project, ground-based narrowband images of Titan from 1999 were utilized at 5 wavelengths surrounding 0.94 [mu]m, as well as Titan images obtained in 2004 at 4 shorter wavelengths, to examine the haze distribution at altitudes below 100 km. Analysis of these observations indicated a clearing haze abundance at altitudes in Titan's upper troposphere/ lower stratosphere. Additionally, HST STIS spectra acquired in 2000 at 122 wavelengths between 0.6 [mu]m and 1 [mu]m were utilized to expand the altitude sensitivity below 100 km by exploiting the transition between optically thick haze at shorter wavelengths and optically thin haze at longer wavelengths. Analysis of the STIS data suggests a strong reduction in haze concentration above Titan's tropopause that varies in degree as a function of latitude. Titan's methane abundance profile is fairly consistent with latitude and longitude and there is evidence for local areas of methane saturation in the troposphere.

For the Mars portion of this project, near-infrared observations of Mars recorded in 2003 using the SpeX instrument at the NASA/IRTF. H- and K-band spectroscopy of Mars was acquired across the 1.6 [mu]m and 2.0 [mu]m CO 2 absorption bands to measure the total extinction optical depth of dust as a function of time-of-day. This work quantifies the variations in the dust abundance over a course of a martian day. The results are consistent with small time-of-day variations in the abundance of martian dust. The implications regarding the aerosol distribution in two Earth-analog objects will be discussed.