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Summary - (Apr 26, 2005) During its recent
Titan flyby, NASA's Cassini spacecraft discovered
that the outer layer of the moon's thick atmosphere is filled with complex
hydrocarbons. Titan is very cold, so scientists expected that these
hydrocarbons would condense out of the atmosphere and rain down on the moon's
surface. Instead, some process of interaction between Titan's atmosphere,
sunlight, and Saturn's magnetic field are keeping them aloft and cycling them
through the atmosphere.
Full Story -
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Image credit: NASA/JPL/SSI
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During
its closest flyby of Saturn's moon Titan on April 16, the Cassini
spacecraft came within 1,027 kilometers (638 miles)
of the moon's surface and found that the outer layer of the thick, hazy
atmosphere is brimming with complex hydrocarbons.
Scientists believe that Titan's atmosphere may be a laboratory for studying
the organic chemistry that preceded life and provided the building blocks for
life on Earth. The role of the upper atmosphere in this organic
"factory" of hydrocarbons is very intriguing to scientists,
especially given the large number of different hydrocarbons detected by Cassini during the flyby.
Cassini's ion and neutral mass spectrometer detects
charged and neutral particles in the atmosphere. It provides scientists with
valuable information from which to infer the structure, dynamics and history
of Titan's atmosphere. Complex mixtures of hydrocarbons and carbon- nitrogen
compounds were seen throughout the range of masses measured by the Cassini ion and neutral mass spectrometer instrument.
"We are beginning to appreciate the role of the upper atmosphere in the
complex carbon cycle that occurs on Titan," said Dr. Hunter Waite,
principal investigator of the Cassini ion and
neutral mass spectrometer and professor at the University
of Michigan, Ann Arbor.
"Ultimately, this information from the Saturn system will help us
determine the origins of organic matter within the entire solar system."
Hydrocarbons containing as many as seven carbon atoms were observed, as well
as nitrogen- containing hydrocarbons (nitriles).
Titan's atmosphere is composed primarily of nitrogen, followed by methane,
the simplest hydrocarbon. The nitrogen and methane are expected to form
complex hydrocarbons in a process induced by sunlight or energetic particles
from Saturn's magnetosphere. However, it is surprising to find the plethora
of complex hydrocarbon molecules in the upper reaches of the atmosphere.
Titan is very cold, and complex hydrocarbons would be expected to condense
and rain down to the surface.
"Biology on Earth is the primary source of organic production we are
familiar with, but the key question is: what is the ultimate source of the
organics in the solar system?" added Waite.
Interstellar clouds produce abundant quantities of organics, which are best
viewed as the dust and grains incorporated in comets. This material may have
been the source of early organic compounds on Earth from which life formed.
Atmospheres of planets and their satellites in the outer solar system, while
containing methane and molecular nitrogen, are largely devoid of oxygen. In
this non-oxidizing environment under the action of ultraviolet light from the
Sun or energetic particle radiation (from Saturn's magnetosphere in this
case), these atmospheres can also produce large quantities of organics, and
Titan is the prime example in our solar system. This same process is a
possible pathway for formation of complex hydrocarbons on early Earth.
This was Cassini's sixth flyby of Titan, but its
exploration has just begun. Thirty-nine more flybys of this strange, remote
world are planned during Cassini's nominal mission.
The next Titan flyby is August 22.
The latest images from the Titan flyby are available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini . The Cassini-Huygens mission is a cooperative project of NASA,
the European Space Agency and the Italian Space Agency. JPL, a division of
the California Institute of Technology in Pasadena,
manages the Cassini mission for NASA's Science
Mission Directorate, Washington,
D.C.
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