18 January 2005--European and American scientists last Saturday morning unveiled the very first scientific results sent back from the Huygens Titan probe following its triumphant landing on Saturn's largest moon. Though bleary-eyed from their all-night vigil, the scientists gave a presentation that delighted a crowd of journalists and staff assembled at the European Space Agency's Space Operations Centre in Darmstadt, Germany.
In Living Color
An image from the Huygens landing site on Titan. The rock-like objects may be ice blocks. The two just below the middle of the image are 15 cm (left) and 4 cm (center) across and are 85 cm from the probe
A joint project of NASA, the European Space Agency (ESA), and the Italian Space Agency, the Cassini-Huygens orbiter-lander mission was conceived 25 years ago to explore Saturn and its moons. Piggybacked on the Cassini orbiter, the Huygens lander, named for the 17th-century astronomer who discovered Saturn's rings and Titan, was the European part of the mission. On Friday, the 3-meter-wide flying-saucer-shaped probe plunged through Titan's thousand kilometer thick atmosphere, braving extremes of heat and turbulence before coming to rest intact on the moon's surface.
Images of Titan had previously been taken by Cassini earlier in its mission and before it by the Voyager probes in the early 1980s. But the pictures frustrated scientists because of how hard it is to discern the surface through Titan's thick, hazy atmosphere. In contrast, the data sent back from Huygens reveal with remarkable clarity features that evoke things like riverbeds, rocks, and ground fog.
"We are the first visitors of Titan, and the scientific data that we are collecting now shall unveil the secrets of this new world," exulted ESA chief, Jean-Jacques Dordain.
"It's almost impossible to resist the speculation that this flat, dark material is some kind of drainage channel," said Marty Tomasko, team leader for the Huygens imaging component, about one image, "that we're seeing some kind of shoreline, that we don't know whether this still has liquid in it, or whether the liquid has drained away or drained into the surface." Indeed, experiments by the surface science team indicate that the Huygens's landing site may have the consistency of "wet sand or clay" topped by a thin crust, leading one scientist to draw an analogy to créme brûlée.
Scientists will spend years poring over the trove of data returned during the few hours of transmission from Huygens as it descended through the atmosphere and landed on the surface, mirroring the years it took to get Huygens to Titan.
After about a quarter-century of planning, the lumbering Cassini finally headed into space in 1997 with Huygens strapped to its back. It was heralded as the last of the giant-sized, big-ticket unmanned space missions.
But the seven-year Cassini voyage was not without incident, and the Huygens mission was almost stillborn. In 2000, ESA engineer Boris Smeds discovered a flaw in the hardware onboard Cassini used to receive Huygens's once-in-a-lifetime transmissions before relaying them back to Earth (see "Titan Calling" IEEE Spectrum, October 2004). The flaw meant that as the smoggy atmosphere of Titan braked Huygens, the deceleration would cause its transmission frequency to shift due to the Doppler effect, and as built, Cassini's receiver couldn't accommodate the shift.
Smeds's findings started a massive chain reaction in NASA, ESA, and the mission's contractors to find a fix. The solution involved altering Cassini's trajectory, so that the orbiter would travel almost parallel to Huygens's line of descent, reducing Doppler shift to manageable levels.
So even though he was not an official member of the Huygens landing team, it was no surprise to find that Smeds was sitting in the Huygens control room waiting to see if the fix worked and for the data to flow onto their screens.