Washington: Scientists analyzing data from NASA`s Cassini mission have confirmed the presence of a population of complex hydrocarbons in the upper atmosphere of Saturn`s largest moon, Titan, that later evolve into the components that give the moon a distinctive orange-brown haze.
The presence of these complex, ringed hydrocarbons, known as polycyclic aromatic hydrocarbons (PAHs), explains the origin of the aerosol particles found in the lowest haze layer that blankets Titan`s surface.
Scientists think these PAH compounds aggregate into larger particles as they drift downward.
"With the huge amount of methane in its atmosphere, Titan smog is like L.A. smog on steroids," said Scott Edgington, Cassini deputy project scientist based at NASA`s Jet Propulsion Laboratory, Pasadena, California.
"These new papers using Cassini data shed light on how the heavy, complex hydrocarbon molecules that make up Titan`s smog came to form out of the simpler molecules in the atmosphere. Now that they have been identified, the longevity of Cassini`s mission will make it possible to study their variation with Titan seasons," he added.
Aerosols in Titan`s lower haze have been studied using data from the descent of the European Space Agency`s Huygens probe, which reached the surface in 2005, but their origin remained unclear.
New studies analyzing data from Cassini`s visual and infrared mapping spectrometer (VIMS) gathered in July and August 2007 might solve the problem.
One new study of Titan`s upper atmosphere in the Astrophysical Journal describes the detection of the PAHs, which are large carbon-based molecules that form from the aggregation of smaller hydrocarbons.
"We can finally confirm that PAHs play a major role in the production of Titan`s lower haze, and that the chemical reactions leading to the formation of the haze start high up in the atmosphere," said this paper`s lead author Manuel Lopez-Puertas from the Astrophysics Institute of Andalucia in Granada, Spain.
"This finding is surprising: we had long suspected that PAHs and aerosols were linked in Titan`s atmosphere, but didn`t expect we could prove this with current instruments," Lopez-Puertas added.