Mars and Titan: Revealing Ancient Secrets, Raising New Mysteries

From the first hours that the Huygens space probe plunged through a murky atmosphere to land on the surface of Titan last month, scientists in Europe and the United States saw Saturn's biggest moon as a cousin, of sorts, to Earth. With cameras and infrared spectrometers, they could see what appeared to be hills, lakes and stream beds, perhaps volcanoes, and plenty of fog.

But for all of the similarity, top mission scientists told reporters at the AAAS Annual Meeting Friday that Titan is a world of icy desolation, where the possibility of life may have been thwarted by temperatures of minus 290 degrees F.

If the cold prevented the chemical reactions that might produce life, however, it could allow scientists "a kind of time-travel" back to "the earliest days of the solar system," said astronomer Tobias Owen, considered one of the godfathers of the mission. "Titan is the Peter Pan of our solar system. It's a little world that never grew up."

Owen, a University of Hawaii astronomer, appeared at a Washington D.C. news conference with three other first-rank American space scientists: Dennis Matson, the Cassini project scientist; Jonathan Lunine, an interdisciplinary scientist on the mission; and Steven Squyres, the principle scientific investigator on the Mars Rover mission.

The Cassini and Mars projects had been decades in the making, but in the space of the past 13 months, they have achieved a stunning exploration of two bodies that may have much to tell us about the possibility of life beyond Earth.

The Mars mission has developed conclusive evidence that water existed there eons ago. That research won the 2004 "Breakthrough of the Year" recognition from the journal Science (which is published by AAAS). And while the Huygens space probe landed a little over a month ago, scientists are fascinated with the research and discovery that is getting under way.

"It's going to get more interesting," Matson said in an interview. "It's a very strange place. It's been so much more than I'd imagined."

The Cassini-Huygens mission is a joint-venture of the European Space Agency, the Agenzia Spaziale Italiana and NASA. It has been described as the most ambitious effort in planetary space exploration ever undertaken. NASA's Cassini craft carried the Huygens probe on a flight that began in 1997, arriving at Saturn last July. Huygens was dispatched to Titan in December, and parachuted to the surface on 14 January.

Tobias Owen Photo by Edward W. Lempinen

"We were stunned by what we saw," Matson told reporters. Some of the first aerial shots taken by Huygens as it neared the surface looked like a river-laced hills rolling down to a seacoast. "Any geomorphologist could look at that and tell you of the processes that have formed it," Matson said. "That's the tantalizing part-it looks so familiar…but we're not sure if that's the correct story or not."

For example, it may have been liquid methane that carved the stream beds. And where one would find sand on an earthly stream bed, on Titan one might find fine grains of water-ice.

But in recent days, the mission has used radar to discover features that are completely unfamiliar, said Lunine, who spoke to the press conference by telephone. There were "mysterious dark streaks" that look like cat scratches, he said-sand dunes, perhaps, or maybe geological formations. And this week the scientists discovered an impact crater roughly the size of the state of Iowa, 440 kilometers (270 miles) across.

"This is a very dynamic world with a complex history that Cassini-Huygens probably is only beginning to elucidate," said Lunine, who is based at the University of Arizona in Tucson.

Owen cautioned that scientists don't expect to find life on Titan. But, he said, they might find "primordial ice cream"-a frosty stew of chemicals that could, in more favorable conditions, be precursors to life.

While the Titan research is just beginning in earnest, Squyres and the team of scientists and engineers on the Mars mission know the rovers' days are numbered. The rovers Spirit and Opportunity were designed to operate for 90 days on Mars' surface, and yet they have been hard at work for over a year.

During the news conference, and in a plenary address at the Annual Meeting Friday night, Squyres said the strategy is to work hard until the rovers give out-whether from power loss, mechanical failure, electrical malfunction or some other cause.

Dennis Matson Photo by Edward W. Lempinen

In the past, Squyres has acknowledged an almost familial affection for rovers. "As much as we'd like to think these vehicles are immortal," he told reporters Friday, "...there is a sense of urgency. We want to get to high-priority targets while there's still time."

Opportunity, for example, is now aimed at a field of rich, unusual "etched terrain" two kilometers south of its current location. The rover recently traveled a record 156 meters in a day, Squyres said.

Still, the rovers show no sign of giving out. And Squyres seemed philosophical about the elements of hard work, longevity and luck in space research.

The rover Spirit was stuck at the base of a small hill one recent Martian day, he said, and as it attempted break free, one of its wheels churned several inches into unusually soft soil. On Earth, crews guiding Spirit's movement and cameras happened to notice a bright-colored debris in the churned dirt.

It was an exciting discovery, and when the substance proved to have a high salt content, the scientists from the Mars Rover mission had further evidence that large quantities of salty water may have covered parts of the red planet eons ago.

It was just another discovery in a pioneering space mission, one that entailed years of preparation by a team of hundreds. But for Squyres, the moment was also a reminder of the crucial role of serendipity. "In order to find this really good stuff," he said, "we've had to drive four kilometers over 400 days. It just shows you the importance of longevity in a mission."

— Edward W. Lempinen

18 February 2005