Huygens Sends Images of Titan

Stefan Lovgren
for National Geographic News
Updated January 17, 2005
Twenty days after being jettisoned by its mothership, the Huygens space probe plunged through the hazy atmosphere of Titan early Friday morning and landed on the Saturn moon.

Huygens has since sent dozens of images back to Earth (see the first color image from Huygens alongside this article), revealing the first glimpses of the moon's surface. The images show an Earthlike surface strewn with what are thought to be blocks of ice.

Images made by the probe during its parachute descent through Titan's atmosphere reveal what scientists say looks like a shoreline and drainage channels, perhaps for liquid methane. Titan is much too cold for water to exist in liquid form.

Scientists hope the data could help unlock the mystery of Saturn's biggest moon and yield answers to fundamental questions about chemistry and physics, planetary formation, and the conditions that gave rise to life on Earth.

As the second largest moon in our solar system, Titan has long intrigued scientists. Its atmosphere and surface composition are thought to resemble those of the Earth at the time of our planet's formation.

"Titan is sitting up there perking away as kind of a planet-scale chemistry lab doing a lot of the stuff that was going on in the Earth's atmosphere four billion years ago," said Torrence Johnson, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. Johnson is a member of the imaging-science team on the Cassini spacecraft.

Wake-Up Call

Launched in 1997, the Cassini-Huygens mission is jointly managed by NASA, the European Space Agency, and the Italian Space Agency. It arrived in Saturn's orbit on July 1, 2004, for a four-year mission to study the planet, its rings, and moons.

Saturn is the second largest planet in our solar system, after Jupiter. It is composed mostly of hydrogen and helium gas, making it the least-dense planet in our solar system. It has 31 known moons, 13 of which were discovered after Cassini was launched.

Huygens, which has spent the last seven years bolted to Cassini, was jettisoned by the spacecraft on Christmas Day. For 20 days the clam-shaped, 8.9-foot-wide (2.7-meter-wide), 703-pound (319-kilogram) probe has been plummeting toward Titan.

During its descent, all systems were shut down, except for three timers designed to wake up the probe four hours before its landing.

On arrival, the probe was expected to travel at about four miles a second (six kilometers a second). Huygens was designed to deploy a series of parachutes and open a communications link with Cassini to relay images and scientific data to Earth.

Thick Smog

During its two-and-a-half-hour descent through Titan's atmosphere, the probe was expected to send more than a thousand images and details about the lunar atmosphere's structure, composition, and winds.

"We should get a pretty thorough understanding of both the chemistry of the atmosphere and also what's going on at different altitudes of the atmosphere," Johnson said before the probe's arrival at Titan.

The atmosphere of Titan extends ten times farther away from the surface than the Earth's atmosphere does. Titan's atmosphere is composed of nitrogen, methane, and other organic compounds. Scientists believe the chemistry there is similar to that of Earth's before life evolved on our planet.

Data gleaned from the cameras and gas analyzers aboard Huygens may provide clues about the origin of life on Earth.

"It's like looking back in time, to a certain extent," Johnson said. "Imagine taking this chemical melting pot common in the Earth's atmosphere [billions of years ago] and putting it in cold storage, and you get Titan today."

Unknown Surface

The probe was expected to land just south of Titan's equator. But scientists were not sure what it would land in or on: ice, a sea of methane, or something else.

"Will Huygens splash or splat?" Bruce Betts, director of projects at the Planetary Society in Pasadena, said before the landing. "As an example of how we continue to understand Titan, there continues to be uncertainty as to how much of its surface is solid and how much is liquid."

After landing, the probe was expected to have no more than two hours to relay images about Titan's surface before Cassini drifted over the horizon, severing communications forever.

Titan's atmosphere is so thick that it has been impossible for scientists to determine what the surface of this moon looks like. Recent images of Titan taken by cameras aboard Cassini have only added to the mystery.

Showing light and dark patches, the images lack any sign of impact craters, suggesting that geologic activity or weathering has erased them.

"We can't really interpret what we're seeing," Johnson said.

It is highly unlikely that life exists on Titan. With a surface temperature of minus 180 degrees Celsius (minus 292 degrees Fahrenheit) and barely illuminated by the distant sun, Titan is not believed to have the warmth or light essential for life.

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