Scientists say new images from the U.S.-European Cassini spacecraft support the view that Saturn's giant moon, Titan, has conditions similar to that of early Earth before life appeared. As expected, it has detected the presence of organic chemicals in the atmosphere and ground that are the precursors to life.
During its close encounter with Titan Tuesday, Cassini bounced radar and microwave beams off the moon's surface to sense its topography and composition. These signals easily penetrate the smoggy atmosphere, which has long prevented a close look at the heavenly body.
The images derived from the returned signals have delighted members of the imaging team, like University of Arizona planetary scientist Jonathan Lunine.
"Just the information gathered from this first fly-by has been so significant in advancing our understanding of Titan that I think we can look forward to revealing all of Titan's nature over the next four years," he said.
That nature became more apparent with the radar and microwave images, which scientists say show what appears to be a geologically active body, possibly with liquids on the surface and winds creating waves and blowing material around on the ground.
The evidence for wind is seen in bright areas on the images looking like streaks, as if it were dust or sand blown by a gust. The possibility of liquids is shown in dark regions on a radar image that U.S. space agency radar mapper Charles Elachi says is consistent with the way a fluid would appear -- specifically, a fluid made of organic, or carbon compounds.
"These are a very dark areas and it's some of the darkest we have seen in radar images," he added. "That's why we think this might be a liquid area, for the signal comes, hits the surface, and bounces away, so we don't get any return back from it. That's normally what we look on Earth at lakes, so that could be some kind of organic liquid area."
Scientists have known that Titan's mostly nitrogen atmosphere also contains a significant amount of the organic compound methane, a carbon-hydrogen mixture. Cassini's atmospheric sensing instruments have revealed other carbon compounds, too, such as benzene and acetylene. Researchers assume hydrocarbons rain down, perhaps creating organic lakes or depositing such compounds elsewhere on the frigid moon's surface.
Jonathan Lunine says a major reason Cassini will inspect Titan many more times over the next four years is to shed light on a chemical process that could explain how life appeared on Earth.
"On the early Earth, there were organic molecules before there was life," he explained. "Somehow the chemistry of those molecules proceeded in such a way that something we call life began. You cannot study that process in the natural environment of the Earth today, so one has to find a place elsewhere in the solar system and Titan is a potential place."
Mr. Lunine says if the Cassini mission to Saturn finds firmer proof of an organic-rich environment on Titan, a future mission could be sent to collect samples.