Pictures show active world shaped by cryogenic liquids
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: January 14, 2005
Initial pictures of Saturn's moon Titan snapped by Europe's Huygens probe during its historic atmospheric descent and touchdown today show an active world likely carved by the flow of cryogenic liquids that may still pool on its frigid surface, a leading planetary scientist says.
"Surprises are always the things that get you," said Torrence Johnson, a member of NASA's Cassini imaging team at the Jet Propulsion Laboratory in Pasadena, Calif. "We'd hoped for a strange surface, it's always nice to see something like a science fiction movie or whatever, but this is exceeding our expectations.
"I mean, this is not a landscape filled with impact craters and a few ridges and hills. It's an active, living place that's interacting with its atmosphere just like Earth and ancient Mars did. And yet it's doing this in a completely different environment, where it's not water and rain from clouds of water that are doing things. You're dealing with what we would regard as cryogenic things here on the Earth, cold liquid gases, basically, and yet it's producing a place that looks strangely familiar."
The European Space Agency released three images from Huygens' camera late today, showing the looming surface from 10 miles up, from five miles and finally, from the surface itself. The first image shows what appear to be erosion-carved gullies snaking down through light-shaded terrain to what looks like a long shoreline bordering a dark, featureless plain. Or lake.
Scientists speculated for years that ethane and methane should exist in liquid form on Titan's surface because of the nature of its nitrogen-dominated atmosphere, low temperatures and other factors. But recent ground-based observations seemed to rule out the possibility of global oceans. Initial data from the Cassini orbiter that carried Huygens to Titan found no definitive evidence of smaller bodies of liquids.
But the Huygens photo indicates liquids almost certainly flowed in the past, if not the present. They also show light-shaded areas seen in Cassini orbiter photos likely are slightly elevated and that darker areas are relatively flat, lower-lying features. The latter are candidates for past or present lakes or flood plains.
"It also implies very strongly that the light area is, in fact, slightly elevated because you don't have stream channels that run up hill. They all run downhill, and it looks like a lot of that darker area is, in fact, smooth, dark area. Now, we don't know whether that's liquid now, but it certainly looks like liquid and in this case, water is not what we're talking about. On Mars, when you're talking liquid and liquid erosion, you're talking water. On Titan, what you're talking about with the temperatures at Titan's surface, less than 300 degrees below zero Fahrenheit, the only thing that's liquid is natural gas. And that's coming out of the atmosphere, liquid ethane and methane.
"So these channels have probably been cut in slightly elevated ice, which is playing the role of rock, and then producing tarry substances that run down hill and make these smooth areas," Johnson said. "How long ago that occurred, whether there's still liquid in some of those areas, we don't know. But a picture like that can really start unlocking some of the mysteries we've been debating about looking at the data from the orbiter. And in turn, that means we can take the orbiter data and get a much better global perspective about what's going on on Titan."
"It's probably ice, water ice," Johnson said. "Water ice is a really good rock at the temperatures at Titan's surface. Again, to a geologist, that shouts erosion and you see the blocks are rounded like rocks in the bottom of a stream bed on Earth."
While no liquids are visible in the picture, "I think most of my geological colleagues would agree that what's happened here, we're probably looking at an area that's flowed out from someplace that has been eroded by these ethane, methane liquids, it carried ice boulders of water ice with them, rounded them in the process and left them in sort of an outwash plain."
Johnson said the data seen today represents "the tip of the iceberg."
"These are just a few snippets out of the data set from the images alone," he said. "We also have a vast array of chemical data about the atmosphere. ... In the next few days, we'll start getting detailed read outs about what's in the atmosphere, what's raining down on the surface and what that surface looks like in great detail."