Methane Abundance on Titan, Measured by the Space Telescope Imaging Spectrograph

Abstract

Although methane is the dominant absorber in Titan's reflection spectrum, the amount of methane in the atmosphere has only been determined to an order of magnitude. We analyzed spectra from the Space Telescope Imaging Spectrograph, looking at both a bright surface region (700-km radius) and a dark surface region. The difference between the spectra of the two regions is attributed to light that has scattered off the surface, and therefore made a roundtrip through all of Titan's methane. Considering only absorption, the shape of the difference spectrum provides an upper limit on methane abundance of 3.5 km-am. Modeling the multiple scattering in the atmosphere further constrains the methane abundance to 2.63 ± 0.17 km-am. In the absence of supersaturation and with a simplified methane vertical profile, this corresponds to a surface methane-mole fraction near 3.8% and a relative humidity of 0.32. With supersaturation near the tropopause, the surface methane mole fraction could be as low as 3%. c 2002 Elsevier Science (USA)

Fluvial network analysis on Titan: Evidence for subsurface structures and west‐to‐east wind flow, southwestern Xanadu

“…Titan, like Earth, has a solid surface covered with a substantial atmosphere. Each of these atmospheres contains volatiles—hydrocarbons on Titan, water on Earth—at a few mass percent that are close to their triple points under ambient conditions [e.g., Lemmon et al , 2002; Niemann et al , 2005]. Data from the Cassini‐Huygens mission support the occurrence of methane rainfall and precipitation runoff [ Lunine et al , 2008].…”

Measurements of N 2 -broadening and pressure-shift coefficients in the ν 3 -band of 12 CH 4 using a cw-OPO

“…Methane is known as one of the major greenhouse gases on Earth [10] and a minor constituent of the atmospheres of Jupiter [11], Mars [12] and Titan [13]. The accurate knowledge of its spectroscopic parameters like self-and foreign-gas pressure-broadening and pressureinduced line shift coefficients is extremely useful for the interpretation and modeling of high-resolution infrared spectra of terrestrial and planetary atmospheres.…”

O2- and air-broadening coefficients in the band of 12CH4 at room temperature

“…In this purpose, the scientists need very precise measurements [1] concerning all the atmospheric components. In addition, methane is also a minor constituent of the atmosphere of some planets and satellites of the solar system [2][3][4]. Spectral parameters of this molecule are thus of big interest for the interpretation of remote sensing measurements of the planetary atmospheres.…”