29 November 2007
Organic ‘building blocks’ discovered in Titan’s atmosphere
Scientists analysing data gathered by Cassini have confirmed the presence of
heavy negative ions in the upper regions of Titan’s atmosphere. These
particles may act as building blocks for more complicated organic molecules.
The discovery was completely unexpected because of the chemical composition
of the atmosphere (which lacks oxygen – responsible for forming negative
ions in the lower ionosphere of the Earth – and mainly consists of nitrogen
and methane). The observation has now been verified on 16 different
Prof Andrew Coates, researcher at University College London’s Mullard Space
Science Laboratory and lead author of the paper, says: “Cassini’s electron
spectrometer has enabled us to detect negative ions which have 10 000 times
the mass of hydrogen. Additional rings of carbon can build up on these ions,
forming molecules called polycyclic aromatic hydrocarbons, which may act as
a basis for the earliest forms of life.”
Coates added, “Their existence poses questions about the processes involved
in atmospheric chemistry and aerosol formation and we now think it most
likely that these negative ions form in the upper atmosphere before moving
closer to the surface, where they probably form the mist which shrouds the
planet and which has hidden its secrets from us in the past. It was this
mist which stopped the Voyager mission from examining Titan more closely in
1980 and was one of the reasons that Cassini was launched.”
The new paper builds on work published in Science on 11 May where the team
found smaller tholins, up to 8000 times the mass of hydrogen, forming away
from the surface of Titan.
Dr Hunter Waite of the South West Research Institute in Texas and author of
the earlier study, said: “Tholins are very large, complex, organic molecules
thought to include chemical precursors to life. Understanding how they form
could provide valuable insight into the origin of life in the solar system.”
Notes for editors:
The findings published yesterday, 28 November, in the Geophysical Research
Letters appear in ‘Discovery of heavy negative ions in Titan’s ionosphere’.
The authors are: A. Coates, F. Crary, G. Lewis, D. Young, J. Waite Jr. and
E. Sittler Jr.
The Cassini-Huygens mission is a cooperative project between NASA, ESA and
the Italian Space Agency.
The Jet Propulsion Laboratory (JPL), a division of the California Institute
of Technology, manages the Cassini-Huygens mission for NASA’s Science
Mission Directorate. JPL designed and assembled the Cassini orbiter. ESA
developed the Huygens Titan probe, while ASI managed the development of the
high-gain antenna and the other instruments of its participation. The
imaging team is based at the Space Science Institute, USA.
[NOTE: Images supporting this release are available at