Titan's 5 mu m spectral window: Carbon monoxide and the albedo of the surface

We have measured the spectrum of Than near 5 mu m and have found it to be dominated by absorption from the carbon monoxide 1-0 vibration-rotation band. The position of the band edge allows us to constrain the abundance of CO in the atmosphere and/or the location of the reflecting layer in the atmosphere. In the most likely case, 5 mu m radiation is reflected from the surface and the mole fraction of CO in the atmosphere is qCO = 10(-5)(+10) ppm, significantly lower than previous estimates for tropospheric CO. The albedo of the reflecting layer is approximately 0.07(-0.01)(+0.02) in the 5 mu m continuum outside the CO band, The 5 mu m albedo is consistent with a surface of mixed ice and silicates similar to the icy Galilean satellites, Organic solids formed in simulated Titan conditions can also produce Similar albedos at 5 mu m. (C) 1996 Academic Press, Inc.