Huygens is first Earth space probe to land on a world in the outer Solar System. The Cassini-Huygens mission, jointly developed by NASA, ESA and ASI, the Italian Space Agency, began in October 1997. More than seven years later, on 25 December 2004, Huygens was released from the Cassini mothership. It then cruised for 20 days and four million kilometres before reaching Titan’s outer atmosphere.
|Huygens touches down on Titan; Image © ESA|
Huygens started its descent through Titan’s clouds from an altitude of about 1 270 km, decelerating from 18 000 to 1 400 km per hour in just three minutes. A sequence of parachutes then slowed it 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. Scientists later confirmed that the probe had landed safely, on a solid surface.
“Titan was always the target in the Saturn system where the need for ‘ground truth’ from a probe was critical,” says David Southwood, Director of ESA’s scientific programme. “It is a fascinating world and we are now eagerly awaiting the scientific results.”
Huygens began transmitting data to Cassini four minutes into its descent and continued to transmit after landing and as long as Cassini was above Titan’s horizon. That Huygens was alive was confirmed when the Green Bank radio telescope in West Virginia, USA, picked up the probe’s faint but unmistakable radio signal. Radio telescopes on Earth continued to receive this signal well past the probe’s expected lifetime.
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, Germany. Scientific analysis is now ongoing.
Images from another world
Scientists and space enthusiasts were wowed by the first raw images sent back from the Huygens probe. In one frame, the onboard camera shows the surface of Titan through an orange haze, with ice blocks scattered about. In another, taken during the descent, a liquid methane sea meets a misty shoreline, complete with drainage channels.
|A Titan shoreline; Image © ESA|
Despite a few technical glitches, project officials say the probe worked extremely well. “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,” concluded Dordain.