The Cassini-Huygens mission could enable to improve our knowledge on the chemical mechanisms which led to the appearance of life on the Earth.

The spacecraft and its passenger have been launched on October 15 1997 and were inserted in orbit around Saturn on July 1st 2004 after a cruise of 7 years and 3.5 billions of kilometers. The orbiter mission was to collect essential data on Saturn's structure and environment and its natural satellites during 4 years. In April 2008, NASA announced the extension of the mission duration to September 2010. On February 3 2010, NASA announced a second extension of the mission duration to May 2017. On November 19 2010, ESA announced the extension of its participation to the mission exploitation until 2014. ESA will decide later for the 2015-2017 period.

The Huygens module

December 25 2004, the Huygens module separates from the Cassini probe so that it goes down in the atmosphere of Titan on January 14, 2005. The module was equipped with an heat shield allowing the protection of the instruments during the atmospheric descent. At 180 km altitude, the opening of the principal parachute makes it possible the descent slow down of the probe. The heat shield is then released and the probe instruments can start to function.
Instrument ACP (Aerosol Collector Pyrolyser) scientific objective is to determine the chemical composition of the aerosols of Titan's atmosphere.
Instrument HASI (Huygens Atmospheric Structure Instruments) measured the physical parameters of the atmosphere, such as the temperature and the pressure.
Instrument DISR (Descent Imager/Spectral Radiometer) allow to study the solar radiation in the atmosphere and its diffusion by the aerosols in the 0.85 - 1.27 µm spectral domain. Astonishing images of surface, having a complex morphology, were obtained by the DISR imager. The Solar flux being very absorbed at the ground level, a lamp was switched on just before the landing in order to increase the luminosity.
Atmospheric gases were collected and analyzed chemically by instrument GCMS (Gas Chromatograph Mass Spectrometer), which allowed an identification and a measurement of the compounds present.

The descent in the atmosphere of Titan lasted a little more than 2 hours.
The instruments of the SSP (Surface Science Package) aimed to determine the physical properties of the surface during the few minutes of life envisaged of the probe after its landing. Actually, the weak signal emitted by Huygens was received on Earth during more than one hour after the landing, which proves the quality of this mission! At the landing, a penetrometer located under the probe surface broke though the surface and was pushed down into the planet in order to study its consistency. It was initially compared with the consistency of the "burned cream", a hard and thin crust recovering a soft medium like mud or sand. Today, our comprehension of the data evolved. The ground of the landing site is probably granulous, like a sandy area.

Descent of Huygens probe into Titan's atmosphere


Images of the surface of Titan observed by DISR during the
descent (on the left) and on the landing site (on the right)
Credits ESA/NASA/JPL/University of Arizona

The Cassini probe

The Cassini probe, in orbit around Saturn, studies the giant planet, its rings and its satellites with 12 scientific instruments. The instruments allow varied studies of the Saturn environment (magnetosphere, plasma and charged particles), the atmosphere of Saturn, Titan and Enceladus, as well as the surface of these satellites in different wavelengths, from the radios wavelengths to the UV wavelengths, via the radar, the visible and the infrared wavelengths.

Representation in a relative dimension of the principal satellites of Saturn, Titan being the largest satellite.

Saturn, its (D, C, B, A, F, G, E) rings, and its icy satellites, Mimas, Enceladus, Tethys, Dione, Rhea, in the internal magnetosphere (Image NASA).

The French scientific community is highly mobilized to participate to this mission, with over fifty French scientists selected, of which two scientific responsibles for experiments and three interdisciplinary scientists (IDS): it is the first European community on this mission. The French instrument contributions to Cassini-Huygens mission are numerous but they particularly concern the following two instruments:

ACP instrument (Aerosol Collector and Pyrolyser), instrument collecting aerosols at different altitudes to analyse their chemical composition. This instrument is supplied by Service d'Aéronomie.

HASI instruments suite (Huygens Atmosphere Structure Instrument), sensors for measuring the physical and electrical properties of the atmosphere. This instruments suite is under the scientific responsibility of LESIA.

Apart form its financial contribution to the ESA mandatory programme (for Huygens probe), CNES directly participates - through the national programme - to the realisation of about half of the scientific experiments on board the orbital module and its lander.