CU 'eyes' to examine Titan as probe begins momentous Xmas journey

Saturn's moon Titan, photographed Dec. 11, 2004. NASA/JPL/Space Science Institute

By Larry Klaes

Cornell space scientists, who began 2004 with a spectacular double landing of NASA's rovers Spirit and Opportunity on Mars, will end the year by participating in an equally impressive feat: the attempted landing of a probe on Saturn's largest and most interesting moon, Titan.

On Christmas Day, the Cassini spacecraft, which has been in orbit around Saturn since June 30, will release its 700-pound Huygens probe to begin a long drop towards Titan. Named after the Dutch astronomer who discovered the Saturnian moon in 1655, Huygens will drift through space until it hits Titan's atmosphere on Jan. 15, moving at 10 miles a second. The dense air encountered by the probe will rapidly slow it down, allowing Huygens to drift downward under a deployed parachute for almost three hours.

Nearly 800 million miles away, the events will be closely monitored through Cassini's electronic "eyes" by a Cornell team that includes Joseph Burns, the Irving Porter Church Professor of Engineering, Theoretical and Applied Mechanics, professor of astronomy and Cornell's vice provost for physical sciences and engineering; Joseph Veverka, professor and chair of the Department of Astronomy; astronomy Professors Steve Squyres, Peter Gierasch and Philip Nicholson; and Peter Thomas, senior researcher in astronomy. Though the Cornell team will not play a direct role in the probe's encounter with Titan, their instruments will analyze the giant moon for at least the four years of the main mission, greatly increasing the amount of data returned by Huygens.

Titan is among the most mysterious worlds in the solar system, covered by a thick layer of orange smog in an atmosphere 60 percent denser than Earth's. Scientists have long wondered what lies in and beneath those alien clouds. Some think it could be analogous to what Earth was like in the early days of its history several billion years ago.

Previous space missions to Saturn did not carry the necessary scientific instruments for penetrating Titan's atmosphere. Images from the Hubble Space Telescope and ground-based observatories taken in infrared wavelengths have given only the roughest ideas of surface features on the distant moon.

The Cassini space probe, launched in October 1997, carries two cameras, one with a narrow angle (0.35 degrees field of view) and the other with a wide angle (3.5 degrees). "The narrow angle could easily read a newspaper across the length of Schoellkopf Field," said Burns.

Why does one camera have a field of view 10 times the other? "Because Cassini orbits Saturn in an elliptical path, its distance from items of interest -- the planet, rings and satellites -- varies greatly, so having two different fields of view is very helpful," Thomas explained.

Both cameras use charge coupled devices (CCDs), which are silicon chips that change photons of light into electronic signals that can be used to make images of astronomical objects or to analyze how much light is being received from such objects. Both cameras are equipped with dozens of filters operating between ultraviolet and near-infrared wavelengths. They are ideal for examining the atmosphere of Titan and showing close-up details of the moon's surface. "All the imaging is planned out long in advance. Many Cornellians have spent years planning the exact commands to get all of the images," said Thomas.

Another instrument carried by Cassini that has deep Cornell involvement is the composite infrared spectrometer (CIRS). "CIRS measures the spectrum of thermal radiation emitted by a local region wherever the instrument is pointed," said Gierasch, who is on the instrument team. "The spectrum contains information about the temperature of the emitting material and about the composition of the material."

Nicholson is on the visual infrared mapping spectrometer team. The instrument can detect much longer wavelengths than the CCD cameras. This makes it the prime device for analyzing the chemical makeup of the Saturnian system's surfaces, atmospheres and rings.

During the descent onto Titan, the Huygens probe will scan the surrounding atmosphere to analyze its composition and take more than 1,000 images as it heads toward the surface, which appears to be covered in flows from ice volcanoes, based on recent Cassini data. If Huygens survives the landing, it will relay data for up to 30 minutes before contact is broken with the Cassini orbiter.

"CIRS measurements will give a global context for the atmospheric properties that Huygens measures at the entry site," said Gierasch. And the images taken before and after the probe lands, said Thomas, will provide context for the geology of where the probe comes down, as well as some information on Titan's weather that could affect the landing site.

Cornell postdoctoral associates also heavily involved in Cassini are Paul Helfenstein, Matthew Tiscareno and Matthew Hedman, all in the Department of Astronomy.