FIVE QUESTIONS
Uncovering mysteries of Saturn satellite
By Chris Oliver
Advertiser Staff Writer
 |
| OWEN |
In July, the Cassini-Huygens mission, NASA's biggest, costliest interplanetary explorer, will reach Saturn, orbit the planet and release a probe onto the largest moon, Titan. The mission, which left Earth in October 1997, has been in planning for 20 years.
University of Hawai'i astronomer Tobias Owen has been working on the mission since its beginning. The Advertiser asked him for an extra-terrestrial progress report.
Q. Is the spacecraft still on target for arrival July 1?
A. Yes! In fact, Cassini-Huygens will pass Saturn's distant satellite, Phoebe, on June 11 on its way to Saturn.
Q. Cassini drops a probe onto Titan. How close is Titan to Saturn?
A. Titan is about three times farther from Saturn than the moon is from the Earth. But don't forget that Saturn is about nine times bigger than Earth! Nevertheless, Saturn has such a low density that it would float in Champagne, if only you had a large enough glass!
Q. Why choose Titan for landing a probe?
A. Titan is the biggest of Saturn's satellites, in fact, only Jupiter's moon Ganymede is larger. Both are bigger than the planet Mercury.
But the reason we are concentrating on Titan is not that it is so big, but that it has an atmosphere that is denser than our own. We can send in a probe, Huygens, to descend gently by parachute, making measurements throughout the 2 1/2 hours of its descent. If it survives this landing, it will continue to make observations for about another hour. The mother ship, Cassini, will have then passed over the horizon, so the probe can no longer communicate with it. Shortly after, Huygens will perish from the cold.
Titan gives us an opportunity for cosmic time travel. The chemical reactions going on in Titan's atmosphere today must resemble in some respects what took place on the early Earth. Whereas on Earth, these chemicals formed a "primordial soup" in which life could begin, on Titan we expect something like "primordial ice cream," where all these interesting organic compounds are held in deep freeze, at Titan's low surface temperature of -300 F. So, by travelling to the outer solar system, we can study our past.
Q. What do you expect to find?
Advertiser library photo • 1997
Amazing things! Titan has the largest unexplored surface in the solar system. It may have lakes and seas of liquid natural gas; rainstorms, rivers and waterfalls of liquid ethane and methane. It's possible that the entire landscape of Titan is flammable (It is the dream world of Exxon!), except for the underlying bedrock, which is very cold water-ice, and for the blocks of ice that have been scattered around from impact craters. We'll see the same craters as on Mars, but they will be made in ice instead of rock. Most of the rock on Titan is buried deep, just as for Ganymede and Callisto in the Jupiter system. The probe's microphone will listen for evidence of winds or thunder.
The space probe Cassini-Huygens is expected to discover clues to Earth's history on Titan, a moon of Saturn.
Q. A tour of Saturn and environs by the Cassini spacecraft follows. How long and what is UH's involvement?
The mission will last four years, but we are hoping for two additional years. We expect lots of interesting meteorology on Saturn itself and a plethora of fascinating phenomena in the beautiful system of rings and in the complex magneto-sphere.
The other satellites of Saturn also promise surprising discoveries.
Iapetus has one hemisphere that is darker than coal, while the other is icy and white. We don't know how that happened and we don't know what that dark material is or where it came from.
Enceladus orbits in the middle of a tenuous ring of particles as tiny as those in cigarette smoke. How does it produce that ring? This satellite is only 310 miles across, compared with 2,158 miles for our moon, yet it has large, smooth patches on its bright surface where crater walls have melted away. How did that happen?
Our involvement is by our membership on the teams. (Owen chaired the U.S. team that worked with a European team to define the mission and get it approved, first by the European Space Agency and then by NASA and then by Congress.
I am an interdisciplinary scientist, which means I can work with all of the different experimenters on both the probe and the orbiter to attack the science questions we want to address.
Reach Chris Oliver at 535-2411 or coliver@honoluluadvertiser.com.
