First 'in situ' composition measurements made in Titan's atmosphere(Forwarded)

ESA News
http://www.esa.int

30 November 2005

First 'in situ' composition measurements made in Titan's atmosphere

Unique results from the Aerosol Collector and Pyrolyser (ACP) and the
Gas Chromatograph Mass Spectrometer (GCMS) have given scientists their
first in situ chemical data on Titan's atmosphere, including aerosols,
chemical composition and isotopes.

Two of Titan's key unknowns are the origin of the molecular nitrogen and
methane in the atmosphere, and the mechanisms by which methane is
maintained in the face of rapid destruction by photochemistry (chemical
processes that are accompanied by or catalysed by the emission or
absorption of visible or ultraviolet light).

The GCMS measured chemical composition and isotope abundances from 140
km altitude to the surface and confirmed the primary constituents were
nitrogen and methane, and that the haze in the atmosphere is primarily
methane.

From isotopic ratio measurements, the Huygens scientists obtained two
key findings. The carbon isotope ratio (12C/13C) measured in methane
suggests a continuous or periodic replenishment of methane in the
atmosphere, but no evidence was found of active biological systems.

The nitrogen isotope ratio (14N/15N) suggests to the scientists that the
early atmosphere of Titan was five times denser than it is now, and
hence lost nitrogen to space.

Argon 36 was detected for the first time, but not xenon or krypton.
However, the argon was found in low abundance, which is especially
interesting because of the huge, nitrogen-dominated atmosphere and
because about 50% of the mass of Titan is water ice, known to be a
potentially efficient carrier of noble gases.

This low abundance implies the atmosphere was condensed or captured as
ammonia, instead of nitrogen. The non-detection of the other noble
gases, a surprising finding, will also fuel theories of the origin and
evolution of Titan's atmosphere.

The composition of surface vapours obtained by GCMS after landing shows
that Huygens landed on a surface wet with methane, which evaporated as
the cold soil was heated by the warmer probe. The surface was also rich
in organic compounds not seen in the atmosphere, for example cyanogen
and ethane, indicating a complex chemistry on Titan's surface as well as
in the atmosphere.

Argon 40 was also detected at the surface and its presence indicates
that Titan has experienced in the past, and is most likely still
experiencing today, internal geological activity.

Titan's aerosols play an important role in determining atmospheric
thermal structure, affecting the processes of radiative heating and
cooling. They can help to create warm and cold layers that in turn
contribute to circulation patterns and determine the strengths of winds.

The ACP obtained direct measurements of the chemical make-up of these
aerosol particles. From an analysis of the products obtained by
pyrolysis (chemical decomposition of organic materials by heating) of
aerosols at 600 C, ammonia and hydrogen cyanide were the first molecules
identified.

This is of prime importance because ammonia is not present as a gas in
the atmosphere, hence the aerosols must include the results of chemical
reactions that may have produced complex organic molecules. They are not
simply condensates.

Aerosol particles may also act as condensation nuclei for cloud
formation, and are the end-products of a complex organic chemistry which
is important in astrobiology. Indeed, Titan offers the possibility to
observe chemical pathways involving molecules that may have been the
building blocks of life on Earth.

Notes to editors:

This summary is based on papers which appear on line in Nature, on 30
November 2005.

For more information:

Hasso Niemann, PI Gas Chromatograph Mass Spectrometer
NASA GSFC, Greenbelt, USA
E-mail: Hasso.Niemann @ gsfc.nasa.gov

Guy Israel, PI Aerosol Collector and Pyrolyser
Service d'Aeronomie, Univ. de Paris and Versaillles-Saint Quentin, France
E-mail: guy.Israel @ aerov.jussieu.fr

Jean-Pierre Lebreton, ESA Huygens Mission Manager
E-mail: jplebret @ rssd.esa.int

Related articles

* At Saturn and Titan
http://www.esa.int/SPECIALS/Cassini-Huygens/index.html
* Looking at Mars
http://www.esa.int/SPECIALS/Mars_Express/index.html
* Highlights of ESA's Huygens mission

http://www.esa.int/SPECIALS/Results_...FSULWFE_0.html
* Titan's turbulence surprises scientists

http://www.esa.int/SPECIALS/Results_...KRULWFE_0.html
* Rain, winds and haze during the descent to Titan

http://www.esa.int/SPECIALS/Results_...3TULWFE_0.html
* Tide out on Titan? A soft solid surface for Huygens

http://www.esa.int/SPECIALS/Results_...0TULWFE_0.html
* Huygens 3D animation of Titan's surface
http://www.esa.int/SPECIALS/Cassini-...8G808BE_0.html
* Huygens landing site animation
http://www.lpl.arizona.edu/DISR/

Related links

* Mars Express instruments
http://www.esa.int/SPECIALS/Mars_Exp...C75V9ED_0.html
* Huygens instruments
http://www.esa.int/SPECIALS/Cassini-...W82VQUD_0.html
* Cassini instruments
http://www.esa.int/SPECIALS/Cassini-...182VQUD_0.html

[NOTE: Images supporting this release are available at
http://www.esa.int/SPECIALS/Results_...1TULWFE_1.html
]