HOUSTON, Texas - A leading planetary scientist said that Titan, one of Saturn's moons, should be targeted for a new round of outer planet exploration.

Thanks to new data streaming in from the Cassini mission, said Jonathan Lunine, Professor of Planetary Sciences and of Physics at the University of Arizona in Tucson. Titan deserves prime-time scrutiny, perhaps using an airship to reveal the moon as never before.

"(However) all plans for exploring the outer solar system, more or less, are in complete ruins at the moment," Lunine said during a major lecture at the 37th Lunar and Planetary Science Conference (LPSC), being held here throughout the week.

Lunine said that the scientific community can start with a clean sheet of paper. "We have no baggage or anything that's weighing us down in terms of thinking about what we might do."

A state of mind

The outer reaches of our solar system is not a destination, in the same sense that the Moon and Mars might be, Lunine said. "It's not a place in the sense of a planet...it's a region. Some people might say it's a state of mind...but it's certainly an important element of our solar system," he said.

In that immense expanse of space, most of the mass of our solar system is present today, a region where most of the volume is located, Lunine pointed out. "And it potentially has several places that are of interest in the search for life elsewhere and for clues to the origin of life."

In developing a new outer solar system exploration strategy, Lunine said there are fundamental scientific questions that come to the forefront:

  • How did our solar system arrive at the architecture that it has today?
  • How did the giant planets and their satellite systems form?
  • Are there habitable or interesting pre-biotic environments in the outer solar system? Furthermore, how best to explore them and access those interesting environments from the point of view of life and astrobiology?

In orchestrating a next round of outer solar system study, Lunine focused on both Europa--a moon of Jupiter--and Saturn's Titan.

Europa: Questions and conflicting clues

Perhaps the most "fundamental discovery" of the NASA Galileo mission that surveyed Jupiter and several of its moons from 1995-2003, is that under Europa's icy face is a liquid water layer - a layer that potentially is accessible, Lunine suggested.

But questions and conflicting clues remain about Europa: How thick is that ice crust? Just how variable is that icy covering? Answering these questions can literally plunge scientists into another realm--the prospective that the moon's ocean environment is habitable.

Galileo imagery suggests that the landscape of Europa is "very, very bizarre," Lunine said. A landed vehicle there may or may not survive touching down on the "very intricate and difficult landscape," he said.

More studies are needed at Europa to tease out information about the thickness of the moon's shell of ice, the nature of its surface, and how best to operate landed vehicles on that moon, Lunine said. "Before one can land and drill down into the ocean of Europa there's an awful lot of geophysics that has to be done."

Titan: a subtle, complex place

In his view, Lunine suggested, new data stemming from the ongoing Cassini mission at Saturn--and the European Space Agency's Huygens lander on Titan--bolster the case for returning to that celestial target. It offers astrobiological potential too.

The scientist said he has struggled over Titan compared to investigation of Europa, adding that Jupiter's moon is a fascinating and important target to go to. "And maybe it's the right target to go to first in the outer solar system. But we've tried three times," Lunine said, noting a mission to Europa was most recently deferred in NASA's new budget.

"Titan is so mysterious...so hard to understand and so complex. But that's why it is such a wonderful place," Lunine said. "It's not a world that has one newspaper headline-type feature. It's just a subtle, complex place."

Lunine painted a futuristic picture of airship or balloon exploration craft that pick out landing sites "on the fly"--freely navigating in Titan's winds moving from spot to spot.

Titan is just waiting for us...Titan wants us," Lunine suggested. "There is no body in the outer solar system that is better designed for exploration than Titan."