NASA-International Space Station

The Huygens probe parachuted down to the surface of Saturn's haze-shrouded moon Titan accurately five years ago on Jan. 14, 2005, providing data that scientists on NASA's Cassini mission to Saturn are still building upon today.

"Huygens has gathered significant on-the-scene data on the atmosphere and surface of Titan, providing valuable ground truth to Cassini's ongoing investigations," said Bob Pappalardo, Cassini project scientist at NASA's Jet Propulsion Laboratory.

The Huygens probe, built and managed by the European Space Agency, was bolted to Cassini and rode along during its practically seven-year journey to Saturn. Huygens' crash marked mankind's first and only effort to land a probe on another world in the outer solar system.

Huygens transmitted data for more than four hours, as it plunged through Titan's hazy atmosphere and landed near a region now called as Adiri. Atmospheric density measurements from Huygens have helped engineer’s process calculations for how low Cassini can fly through the moon's thick atmosphere.

Huygens captured the most consideration for providing the first view from inside Titan's atmosphere and on its surface. The pictures of drainage channels and pebble-sized ice blocks astonished scientists with the extent of the moon's similarity to Earth. They showed evidence of erosion from methane and ethane rain.

"It was eerie," said Jonathan Lunine, an interdisciplinary Cassini scientist at the University of Rome, Tor Vergata, and University of Arizona, Tucson, and was with the Huygens camera team five years ago as they combed through the imagery coming down. "We saw bright hills above a dark plain, a weird mixture of light and dark. It was like seeing a landscape out of Dante."

Combining these images with detections of methane and other gasses emanating from the surface, scientists came to believe Titan had a hydrologic cycle comparable to Earth's, though Titan's cycle depends on methane and ethane rather than water. Titan is the only other body in the solar system other than Earth supposed to have an active hydrologic cycle.

Huygens also gave scientists an occasion to make electric field measurements from the atmosphere and surface, revealing a signature consistent with a water-and-ammonia ocean under an icy crust.

While the Huygens probe itself remains inactive on the Titan surface, insights stimulated by the probe continue and ESA has convened a conference this week to extend the discussion, said Jean-Pierre Lebreton, Huygens Project Scientist for ESA.

"Huygens was an exclusive, once-in-a-lifetime mission," he said. "But we still have a lot to learn and I hope it will provide guidance for future missions to Titan."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. Huygens data was sent to NASA's Cassini spacecraft, and was recorded and relayed to Earth by NASA's Deep Space Network. JPL also manages the Deep Space Network.

NASA'S Cassini spacecraft will return to Titan's southern hemisphere on a flyby tomorrow, Jan. 12, dipping to within about 1,050 kilometers (about 670 miles) of the hazy moon's surface. During this pass, the onboard radar gadget will scan Ontario Lacus, the largest lake in the southern hemisphere, in a quest to learn more about the liquid methane and ethane in the lake and obtain more comprehensive topographical information about the shoreline. Titan is the only other body in the solar system in addition to Earth that is known to have stable liquid on its surface.

This will also be the most southern pass in the mission for the ion and neutral mass spectrometer device, which will probe the composition and density of the atmosphere near Titan's south pole. The atmospheric data collected on this pass will be paired with a similar sampling mission near Titan's north pole during the most recent flyby, 16 days earlier.

Cassini last flew by Titan on Dec. 27, 2009 California time, or Dec. 28 Universal Time. Although this newest flyby is dubbed "T65," planning changes early in the orbital tour have made this the 66th targeted flyby of Titan. This flyby also comes two days before the fifth anniversary of the landing of the Huygens probe on the surface of Titan.

The Cassini-Huygens mission is a supportive project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. The Huygens probe, built and managed by the European Space Agency, was bolted to Cassini and rode along during its nearly seven-year journey to Saturn, before being released for its descent through Titan's atmosphere.

Though there are no plans to examine whether Saturn's moon Titan has a Santa Claus, NASA's Cassini will zoom close to Titan's north pole this weekend.

The flyby, which brings Cassini to within about 960 kilometers (600 miles) of the Titan surface at 82 degrees north latitude, will occur the evening of Dec. 27 Pacific time, or soon after midnight Universal Time on Dec. 28.

The encounter will facilitate scientists to gather more detail on how the lake-dotted north polar region of Titan changes with the seasons. Scientists will be using high-resolution radar to scan the large and several lakes in the north polar region for shape-shifting in size and depth. The ion and neutral mass spectrometer team will take baseline measurements of the atmosphere to compare with the moon's south polar region when Cassini flies by that area on Jan. 12. Cassini will also be collecting pictures for a mosaic of a bright region called Adiri, where the Huygens probe landed nearly five years ago.

Cassini will have released the Huygens probe exactly five years and three days before this latest flyby. Huygens began its expedition down to Titan on the evening of Dec. 24, 2004 California time, or early Dec. 25 Universal Time, and reached the surface Jan. 14, 2005.

Cassini last flew by Titan on Dec. 11, 2009 California time, or Dec. 12 Universal Time. Although this latest flyby is dubbed "T64," scheduling changes early in the orbital tour have made this the 65th targeted flyby of Titan.

Like Earth and other planets, Saturn's orbit is not completely circular, but is instead somewhat elliptical and oblique. Because of this, during its southern summer, Titan is about 12 percent nearer to the sun than during the northern summer. As a result, northern summers are extensive and subdued; southern summers are short and extreme.

"Like Earth, Titan has tens-of-thousands-of-year variations in climate driven by orbital motions," Aharonson said. On Earth, these variations, well-known as Milankovitch cycles, are associated to changes in solar radiation, which concern global redistribution of water in the form of glaciers, and are believed to be responsible for ice-age cycles. "On Titan, there are long-term climate cycles in the worldwide movement of methane that make lakes and carve lake basins. In both cases we discover a record of the process embedded in the geology," he added.

"We may have established an example of long-term climate change, similar to Milankovitch climate cycles on Earth, on another object in the solar system," he said.