The Ground Truth of Saturn's Moon Titan

DARMSTADT, Germany, January 17, 2005 (ENS) - The European Space Agency's Huygens probe successfully descended through the atmosphere of Titan, Saturn's largest moon, and Friday landed on its surface. The landing was the climax of a seven year journey through the solar system on board NASA's Cassini spacecraft.

When the first scientific data arrived at the European Space Operations Centre in Darmstadt on Friday afternoon, the scientists were ecstatic. Huygens is humankind's first successful attempt to land a probe on a world in the outer solar system.

"This is a great achievement for Europe and its U.S. partners in this ambitious international endeavor to explore the Saturnian system," said Jean-Jacques Dordain, ESA's director general.

Huygens is expected to provide the first direct and detailed sampling of Titan's atmospheric chemistry and the first photographs of its hidden surface, and also will supply a detailed weather report.

One of the main reasons for sending Huygens to Titan is that the moon's nitrogen atmosphere, rich in methane, and its surface may contain many chemicals of the kind that existed on the young Earth. Combined with the Cassini observations as it continues to orbit Saturn, Huygens will afford an unprecedented view of Saturn's largest moon.

"The Huygens scientists are all delighted. This was worth the long wait," said Dr. Jean-Pierre Lebreton, ESA Huygens Mission Manager.

Following its release from the Cassini mothership on December 25, Huygens reached Titan's outer atmosphere after 20 days and a four million kilometer cruise. The probe started its descent through Titan's hazy cloud layers from an altitude of about 1,270 km at 11:13 CET. During the following three minutes Huygens had to decelerate from 18,000 to 1400 km per hour.


This is one of the first raw images returned by the Huygens probe during its descent to Titan. It was taken from an altitude of 16.2 kilometers (about 10 miles) with a resolution of approximately 40 meters (about 131 feet) per pixel. It apparently shows short, stubby drainage channels leading to a shoreline. (Photo courtesy ESA/NASA/University of Arizona)
A sequence of parachutes then slowed it down to less than 300 km per hour. At a height of about 160 km the probe's scientific instruments were exposed to Titan's atmosphere. At about 120 km, the main parachute was replaced by a smaller one to complete the descent, with an expected touchdown at 13:34 CET. Preliminary data indicate that the probe landed safely, likely on a solid surface.

The probe began transmitting data to Cassini four minutes into its descent and continued to transmit data after landing at least as long as Cassini was above Titan's horizon.

The certainty that Huygens was alive came at 11:25 CET Friday, when the Green Bank radio telescope in West Virginia picked up a faint but unmistakable radio signal from the probe.

Huygens data, relayed by Cassini, were picked up by NASA's Deep Space Network and delivered immediately to ESA's European Space Operation Centre in Darmstadt, where the scientific analysis is now taking place.

"Titan was always the target in the Saturn system where the need for ground truth from a probe was critical. It is a fascinating world and we are now eagerly awaiting the scientific results," says Professor David Southwood, director of ESA's scientific program.

In the first color photos sent back to Earth from Titan appear what first were thought to be rocks or ice blocks. But the objects in the foreground are now known to be smaller. The one on the left just below the middle of the image is 15 centimeters (about six inches) across, and the one on the right is about four centimeters (about 1.5 inches) across. The rocks are at a distance of about 85 centimeters (about 33 inches) from Huygens.


This is the first color image of Saturn's largest moon, Titan. The surface is darker than originally expected, consisting of a mixture of water and hydrocarbon ice. There is evidence of erosion at the base of these objects, indicating possible fluvial activity. The image was taken with the Descent Imager/Spectral Radiometer, one of two NASA instruments on the probe. (Photo courtesy ESA/NASA/Univ. of Arizona)
The Cassini-Huygens mission is a cooperation between NASA, the European Space Agency and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA's Office of Space Science, Washington. JPL designed, developed and assembled the Cassini orbiter.

"Today's achievement proves that our partnership with ESA was an excellent one," said Alphonso Diaz, NASA associate administrator of science.

"The teamwork in Europe and the USA, between scientists, industry and agencies has been extraordinary and has set the foundation for today's enormous success," said Dordain.

"Titan has long intrigued those who watch the planets," wrote Carolyn Porco, Cassini Imaging Team Leader, on January 11.

"It is a Mercury-sized icy body whose surface environment may be, in some respects, more like Earth's than any other in the Solar System. Like Earth's, its atmosphere is thick and largely molecular nitrogen. Unlike Earth's, it is lacking free oxygen and is suffused with small but significant amounts of gaseous methane, ethane, propane, and other simple and not-so-simple organic materials containing hydrogen and carbon. Some of these compounds, methane and ethane, may be liquid at the surface, despite the unimaginable cold of -300 degrees Fahrenheit.

'And though there is no liquid water, what water does on Earth, methane does on Titan. The presence of this simple hydrocarbon as a liquid on the surface and a gas in the atmosphere gives Titan a terrestrial-like greenhouse cycle and a boost in temperature, warming its lower atmosphere," she explains.

"If present-day Titan could be warmed enough to melt its icy exterior, its atmosphere would bear a striking resemblance to that of early Earth, billions of years ago, prior to the emergence of life."

Might Titan be a frozen, pre-biotic Earth," she speculates, "telling a tale littered with clues to the origins of terrestrial life long ago?"