Photochemical aerosols in Titan's atmosphere

The optical properties of polymers, produced photolytically from ethylene, which was detected in Titan's atmosphere and from acetylene or hydrogen cyanide which may be present there, were studied experimentally. It is shown that an aerosol consisting of polyethylene provides an excellent fit to the variation of Titan's albedo with wavelength, while polymers of acetylene or hydrogen cyanide do not. This fit seems to remove the requirement of nitrogen-bearing polymers, which was proposed earlier to account for Titan's red coloration. Therefore, Titan's coloration does not necessarily imply the presence of nitrogen in its atmosphere. It is also proposed that above the layer of larger aerosol particles, whose scattering determines the phase function, there are smaller particles of the same material, which act as an absorbing haze to darken and slightly redden the underlying aerosol. This high-altitude haze also causes the observed strong limb-darkening.