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Huygens was an atmospheric probe designed to make on site observations of the Saturnian moon Titan. It carried to Saturn as part of the Cassini-Huygens mission, a joint venture between ESA, NASA and ASI, the Italian Space Agency. The Huygens probe was the ESA contribution of the mission. The probe was named after the 17th century Dutch astronomer Christian Huygens. The combined Cassini-Huygens spacecraft was launched from Earth on October 15, 1997.
Huygens was designed to enter and brake in Titan’s atmosphere and parachute a fully instrumented robotic laboratory down to the surface. At the time of its inception, it was not yet certain if the landing site would be a mountain range, ocean, or plain, as Titan’s surface was unknown. But the probe was designed to survive impact and splash down on a liquid surface assuming that the likely landing site would be liquid.
The Huygens probe system was made up of two parts. The main part was the probe itself which would descend to Titan. The other part was the probe support equipment. This part of the probe stayed in orbit with the orbiter. The probe itself consisted of an aeroshell to protect the instruments on board during the probe’s entry into Titan’s atmosphere. The second part was the descent module which contained the scientific instrumentation. The descent module was enclosed in the aeroshell.
Power for the Huygens probe after separation was provided with five Lithium Sulfate batteries capable of storing 1600 W-h of energy. It was only planned to supply about 250 W of power long enough for the expected three hours operation originally planned for the probe. Prior to separation all power was provided by the Cassini orbiter.
Navigation to Saturn and getting the spacecraft closer to Titan was a complicated process. It involved heavy cooperation between NASA and ESA monitoring stations as well as the Cassini orbiter.
The landing on Titan’s surface proved to mostly be a complete success. Although Cassini successfully received 350 pictures that it received from Huygens of its descent and landing site, a software error failed to turn on one of the Cassini receivers and caused the loss of an additional 350 pictures.
The probe descended for 2 hours 27 minutes, and was able to transmit for 1 hour 10 minutes on the surface. Throughout the descent and landing, data were collected from all instruments providing a detailed picture of Titan’s atmosphere and surface. The probe had actually landed on an ice plain, and it was able to take pictures, showing a pebble-covered surface. The images suggest that the surface is largely solid, but that pockets of liquids exist. However, it is so cold on Titan that the liquid would not be water, but actually liquid ethane and methane.
The images also suggest a relatively young surface with no obvious craters, with other features resembling drainage channels and, possibly, a shoreline.
While the data from Huygens is still being studied, the probe provided unprecedented information about Titan and helped further expand our knowledge of Saturn’s satellites.
We’ve also recorded an entire episode of Astronomy Cast all about the Cassini Mission. Listen here, Episode 229: Cassini Mission.