On 14 January 2005 the Huygens atmospheric capsule landed on Saturn's moon Titan
On 14 Jan­uary 2005 the Huy­gens at­mo­spher­ic cap­sule land­ed on Sat­urn's moon Ti­tan
Image 1/2, Credit: ESA.

On 14 January 2005 the Huygens atmospheric capsule landed on Saturn's moon Titan

One of the most ex­cit­ing ex­per­i­ments in re­search­ing the So­lar Sys­tem with robot­ic space probes took place on 14 Jan­uary 2005, when the Eu­ro­pean mea­sure­ment cap­sule Huy­gens made a two-and-a-half hour flight through Ti­tan's at­mo­sphere and sub­se­quent­ly land­ed on the icy sur­face of the moon. The pic­ture is an artist's im­pres­sion of the land­ing site. A mech­a­nism eject­ed Huy­gens from the NASA Sat­urn or­biter Cassi­ni on 24 De­cem­ber 2004. Huy­gens start­ed a three-week 'bal­lis­tic' – that is, not us­ing a propul­sion sys­tem – de­scent to­wards Ti­tan. When Huy­gens got to the out­er reach­es of the dense ni­tro­gen at­mo­sphere, the at­mo­sphere of the moon slowed down the probe. In the course of this de­cel­er­a­tion, the pro­tec­tive shield of the cap­sule was heat­ed to 1,500 de­grees Cel­sius. One hun­dred and eighty kilo­me­tres above the sur­face, the first, two-and-a-half-me­tre di­am­e­ter parachute pulled off the heat shield as planned. Im­me­di­ate­ly af­ter­wards, a sec­ond parachute, with a di­am­e­ter of more than eight me­tres, opened so that Huy­gens’ fall was fur­ther slowed and the cap­sule – now a play­thing of Ti­tan’s winds – float­ed through the at­mo­sphere. The probe col­lect­ed and anal­ysed its first sam­ples of the at­mo­sphere and start­ed ac­quir­ing im­ages. The sec­ond parachute was re­leased at a height of 125 kilo­me­tres. A third parachute al­lowed the probe to float down­wards through the clouds. On 14 Jan­uary 2005 at 12:38 Cen­tral Eu­ro­pean Time, Huy­gens land­ed on the sur­face of Ti­tan, which is at a tem­per­a­ture of mi­nus 180 de­gree Cel­sius. The mea­sure­ment da­ta and im­ages from the land­ing site were first trans­mit­ted to Cassi­ni and from there to Earth. Round­ed ice blocks are vis­i­ble which were pre­sum­ably ground down by a flow­ing medi­um. Af­ter a few hours, the ra­dio sig­nals from a sci­en­tif­i­cal­ly and tech­ni­cal­ly mag­nif­i­cent mis­sion ceased as ex­pect­ed.
Artist's impression of the Cassini spacecraft in orbit around Saturn.
Cassi­ni in or­bit around Sat­urn
Image 2/2, Credit: NASA.

Cassini in orbit around Saturn

Artist's im­pres­sion of the Cassi­ni space­craft in or­bit around Sat­urn.

When the Cassini-Huygens mission was launched on 15 October 1997, the entry probe Huygens was mounted on the side of the Cassini orbiter spacecraft, connected by a rotary plate. Huygens spent the seven-year journey to Saturn in 'sleep mode,' only waking every six months for three hours at a time to allow functional checks to be performed.

On 25 December 2004, the small, wok-shaped entry probe separated from Cassini and began its journey to Saturn's moon Titan. After 20 days, Huygens reached Titan's outer atmosphere; the moon's atmosphere stretches 600 kilometres out into space ten times further than Earth's atmosphere does.

Huygens lands on Titan

The successful landing of Huygens on Titan on 14 January 2005 was the first time in the history of space exploration that a scientific mission has reached a body in the outer Solar System.

The probe began its descent through Titan's atmosphere at 11:13 CET, at a height of about 1270 kilometres. During the next three minutes, the probe decelerated from 18 000 to 1400 kph. Next, the first small parachute opened, pulling away the upper heat shield. The larger main parachute then opened, slowing Huygens to less than 300 kph. At a height of about 160 km, the probe's scientific instruments went into action. At around 120 km, the main parachute was discarded and a smaller parachute opened to complete the landing. Huygens touched down on Titan at 13:34 CET.

Scientists received the first reassurance that Huygens was alive and well on at 11:25 CET, when the Green Bank radiotelescope in West Virginia, USA, received the first weak signal from the probe. The first scientific data from Huygens reached ESA's Space Operations Centre (ESOC), in Darmstadt, Germany, on 14 January 2005 at 17:19 CET.

During the two-hour, twenty-eight-minute descent through Titan's atmosphere, Huygens gathered information about the atmosphere and, after landing, Huygens transmitted data for another 90 minutes.

Data from Huygens, which were first transmitted to the Cassini probe to be stored in quadruplicate, were received by NASA's Deep Space Network and sent directly to ESOC in Darmstadt.

Cassini's long journey

The Cassini orbiter's long research expedition through the Saturnian system began upon arrival at Saturn on 1 July 2004. Originally, the mission was scheduled to end on July 2008, but due to its success, NASA extended the mission until 2017.

Cassini will circle Saturn a total of 76 times; these orbits will include 52 close fly-bys of seven of Saturn's 47 moons. To accomplish its orbits around Saturn, the orbiter must perform 45 'swing-by' manoeuvres near Titan to give it extra momentum. These manoeuvres will bring Cassini as close as 950 km to the surface of Titan, enabling the Cassini radar system (RADAR), which can penetrate the moon's atmosphere, to map the surface with high resolution.

Cassini will perform at least six close fly-bys of four other Saturnian moons: Iapetus, Enceladus, Dione and Rhea. These particular moons were chosen because researchers believe, on the basis of earlier data, that they could provide us with clues about the formation of the Saturn system and perhaps even the formation of our Solar System.

Cassini's mission is expected to end on 30 June 2008, four years after arriving at Saturn and 33 days after the last fly-by of Titan, scheduled for 28 May 2008.

  • Elke Heinemann
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-2867
    Linder Höhe
    51147 Cologne
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin

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