Titan's 5 μm Spectral Window: Carbon Monoxide and the Albedo of the Surface

Abstract

We have measured the spectrum of Titan near 5 μm 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 μm radiation is reflected from the surface and the mole fraction of CO in the atmosphere isqCO = 10+10−5ppm, significantly lower than previous estimates for tropospheric CO. The albedo of the reflecting layer is approximately 0.07+0.02−0.01in the 5 μm continuum outside the CO band. The 5 μm 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 μm.