Photographs and radar surveys from the Cassini spacecraft's Tuesday-night flyby of Saturn's mysterious moon Titan are raising more questions than they're answering, say NASA scientists.
The scientists had hoped the spacecraft's 745-mile-high flight over Titan's surface would finally reveal the lakes, craters and other features thought to be on the giant moon. But so far, the images and data returned from Cassini have only shown splattered light and dark patches that just barely resemble features seen on other rocky bodies in the solar system.
"We're left with many different questions," said mission scientist Jonathan Lunine, of the University of Arizona, at a press conference on Thursday.
Lunine likened the images and data received from Cassini to the pieces of a jigsaw puzzle that doesn't have a completed photo on the box as a guide. "We don't know what the final picture is going to look like and the pieces have to be assembled over time," he said.
To make matters more difficult, each of the pieces seem to be a puzzle in itself. Take, for instance, some of the questions now being posed by the scientists -- and the additional questions that they give way to:
What is responsible for the streaks on Titan's surface?
The streaks could be the result of the wind blowing dust around some obstacle, as seems to be the case on Mars, according to some scientists. This is consistent with the theory that Titan is covered in large part by dustlike hydrocarbon particles. But then, what are the obstacles that block the dust?
Why is there so little evidence of impact craters in the images?
So far, photographs of Titan's surface show few bowl-shaped features indicative of craters, like those seen in photos of Venus, Mars or our own moon. Does this mean that Titan is fairly young and has yet to be hit by many asteroids and comets? Or, does it mean that the surface is so dynamic that impact craters are quickly filled in with liquid or dust?
Do the dark areas in the radar images of Titan's surface signify the existence of lakes?
When radar waves are used to create images of surfaces, areas that reflect more radio waves turn up as bright spots, while those that reflect fewer waves appear as dark spots. Some scientists believe the large, dark patches in the Titan images could be lakes full of liquid ethane and propane, which would absorb radio waves. But if this is true, do the lakes have ripples and waves caused by the wind, or are they completely still?
Why aren't methane clouds abundant in the atmosphere?
Until Tuesday, scientists believed the bright clouds at Titan's southern pole were made of methane. But data from Cassini's instruments show that the clouds don't have the chemical "signature" of methane. So what are they made of, then? And why isn't methane playing an important role in the creation of clouds all over Titan, as one would expect, given the high concentration of methane in the moon's atmosphere?
What happened to the "light" nitrogen in Titan's atmosphere?
Though plenty of "heavy" nitrogen exists in Titan's atmosphere, the amount of "light" nitrogen is much less than that found around several planets and our own moon. This suggests that the light nitrogen was lost somehow over a large period. It also raises the question: Why hasn't a portion of the methane in the atmosphere disappeared, too? Is it being replenished from a reservoir somewhere inside Titan?
Fortunately for the scientists -- and for astronomers around the world who are waiting to hear what they have to say -- these questions don't have to be answered right away. Indeed, Cassini will make 44 more flybys of Titan over the next four years, as it continues to study Saturn, its rings and its moons.
A number of those flybys will come even closer than Tuesday's encounter, bringing Cassini within 590 miles of Titan's surface. Additionally, Cassini will release the European Space Agency's Huygens probe in late December, allowing the probe to descend through Titan's atmosphere and crash into its surface -- or splash into a lake -- on Jan. 14.
Scientists are especially interested in solving Titan's mysteries because conditions on the rocky body are thought to mirror those on Earth before life existed.
"There's an enormous amount of additional information to come," said Lunine. "And just the information gathered from this first flyby has been so significant in advancing our understanding of Titan that I think we can look forward to essentially revealing all of Titan's nature over the next four years."
