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white of knuckle, scientist wills titan probe on By Anne Minard
ARIZONA DAILY STAR

When Martin Tomasko, a UA astronomer, started designing the instrument that will serve as the eyes of the Huygens probe, he first fashioned a weighted block of metal to be used in a practice flight.

Called "bricks," the weights are often used as placeholders during the development of instruments destined for space flight. Ideally, the scientist finishes the test model in time for the practice run, and swaps it out for the hunk of metal.

"My son and I used to joke about that," Tomasko says, mimicking his son: " 'Dad, you've got to finish that instrument. Don't let them fly the brick.' "

His son never got to know whether his dad had to fly the brick. It's still a mystery why 23-year-old Daniel died in 1995 while playing basketball - and Tomasko still swallows emotion when he talks about that part of his life. But he says his son's death, along with every other turn his life has taken since the early 1990s, is wrapped up in the Huygens probe. Finally, after hitching a ride for more than seven years aboard its mother ship Cassini, Huygens (pronounced HOY-gens) will take off on its own Christmas Day and begin its approach to Saturn's most famous moon: Titan.

"We've got a lot sunk into this, as you can imagine," Tomasko says. "You don't work on something for 15 years without having a lot of yourself in it."

Tomasko numbers among a close-knit group of about 200 scientists - a good portion of them at the UA - who have poured much of their lives into this mission. The Cassini-Huygens spacecraft was launched from Earth in 1997. Last summer, Cassini started orbiting Saturn, and has been sending back images and data ever since.

Now Huygens, a 3-foot, $700 million probe, is within weeks of finally answering questions about the planet's largest moon - and the only known moon in our solar system with an atmosphere - that astronomers posed more than a decade ago.

Another world

The scientific community doesn't know much about Titan. But the brief encounters it's had with the exotic moon - mostly during flybys en route to other planets - has made astronomers eager for more. The moon is a mysterious ball of rock and ice surrounded by a thick, orange atmosphere, and might experience methane as the Earth does water.

"There could be lakes," Tomasko says. "There could be drainage channels. There could be methane clouds, methane rain."

Methane, which is produced through biological reactions like digestion here on Earth, can exist as a liquid on this planet only if it's put under enough pressure. But at about minus 290 degrees, the surface of Titan is so cold that methane doesn't need pressure to occur in a liquid form.

Titan's atmosphere is a big part of the reason the planet is so intriguing to astronomers.

They'd like to know why it has an atmosphere, when there are other moons about its size - like Jupiter's Ganymede - that don't. They are curious about the chemical reactions that occur on a geologically young body like Titan, because those could shed light on chemical reactions that happened before there was life on Earth. And they think studying the naturally occurring greenhouse gases that form a thick haze over Titan will help us understand the not-as-natural accumulation of greenhouse gases over Earth.

On Saturday, the Huygens probe is expected to begin a nearly three-week cruise toward Titan. It will sail toward the exotic moon while running on just enough power for an alarm clock to tell it when to wake up. Then, around Jan. 14, things will happen fast. Contamination covers will fly off. Radios will turn on and the probe will start transmitting information about Titan's appearance and atmosphere to a 12-foot antenna on Cassini.

Cassini, in turn, will relay the information 883 million miles back to Earth. Right away, the instrument Tomasko built - an assemblage of cameras and other sensing equipment - will send scientists their first close-up images of the surface of the strange moon.

Tomasko sits closer to the edge of his seat, grins and raises a balled fist when he talks about that day: He and about two dozen colleagues from Tucson, along with scientists from all over the world, will huddle with their respective teams at a control room in Germany, and work through the night to decipher the data. The very next day, they'll hold a press conference to tell the world what they've seen.

Tomasko says if there's one thing he wishes he could change about the Cassini-Huygens mission, it would be the speed of the radio link between the two spacecraft. As it is, his instrument will be able to send less than two dozen 36-piece panoramic photos of the surface of Titan. With the technology that's developed on Earth since the probe launched in 1997, Huygens could transmit twice as many images.

"10-year-old technology"

"Basically, the instrument is flying 10-year-old technology," he said, tapping his desk computer with the back of his hand. "This computer is 2,000 times faster than the computer I'm flying."

There are other weird things about launching a mission and then waiting almost a decade for results, says Ralph Lorenz, another UA researcher who has also spent a significant part of his career on the mission. Lorenz has been working on the Titan mission since his graduate school days in Britain, and is a co-leader of the surface science package, another instrument on Huygens.

"It was quite a strange thing early on when the mission was all paper, when it was just designs and ideas, that supposedly all this was going to become reality in 15 years' time . . . it was just surreal," he said. "But then things turn into hardware on the bench, and things get bolted together . . . and off it goes. Now it's becoming very real in our minds."

In a very practical sense, the prolonged travel time has saved the mission. Through a test in 2001 that many astronomers believed to be redundant and unnecessary, NASA's Jet Propulsion Laboratory discovered that the radio link between Huygens and Cassini would have failed under the original plans - which called for Huygens to cast off much earlier and land on Titan Thanksgiving Day. To remedy the problem, engineers had to change the angle the mother ship will fly after it drops off the probe. Now, they think, the transmissions will go off without a hitch.

"Happily, we had the time to fix it," Lorenz said. "That's one of the advantages of outer solar system exploration."

Still, when astronomers working on the Cassini-Huygens mission talk about the coming moment of truth, they are guarded in their optimism.

"Planetary exploration is a risky business," Lorenz says. "There is a chance that things could go wrong."

But Lorenz says - as disappointing as it would be - a failed Huygens probe would not amount to the simple loss of the approximately $700 million cost to build it.

"It's an investment," he says. "It's something that's worth trying. It's a lot of engineering work. New techniques have been learned and developed. New equipment has already been applied to other missions."

Only a beginning

Jonathan Lunine, one of three interdisciplinary scientists for the Huygens probe, has the job of pulling together all the data streaming in from the probe's individual instruments - like Tomasko's cameras - and applying them to the mission's bigger questions.

"We are supposed to be a kind of intellectual glue," he says. Lunine will mine the data for clues about the interaction between Titan's surface and the atmosphere. The other interdisciplinary scientists will try to synthesize findings about chemistry and the possibility of prelife chemical reactions on the surface.

Immediately after Huygens lands, all the scientists involved in the Cassini-Huygens mission will try to make quick statements to the world about what the mission has accomplished. But for the most part, that early information will be limited to whether the probe worked - and what the bird's-eye pictures look like from Tomasko's cameras.

Lunine says it's likely to be a while before the biggest-picture answers come to light.

"One has to bear in mind that the best insights always come a few years later," he says. "Titan itself, I guess you could say, is a good example."

Lunine said the first mission that really shed light on Titan's atmosphere - showing it to be thick with components including nitrogen and methane - was Voyager 1, which flew by Titan in 1980.

"Those papers didn't come out until 1983 and beyond," he said. "It took that long to get all the bugs out of the data."

And for Lorenz, the long-range nature of space science means no time beats the present for planning astronomy's next great trips.

"Cassini was proposed in the early 1980s," he says. "It's not too soon to start thinking about what might come next."