Date: Thu, 27 Apr 2000 10:19:26 -0700 (PDT)
Subject: Tarlike Macro-Molecules Detected In 'Stardust'
Max-Planck-Institute for Extraterrestrial Physics
Dr. Jochen Kissel,
Max-Planck-Institut fur extraterrestrische Physik
phone: ++49/89/32 99-38 17
fax: ++49/89/32 99-35 69
April 26, 2000
Tarlike macro-molecules detected in 'stardust'
Mass-spectrometer CIDA of the Garching based Max-Planck-Institut on the
NASA spacecraft STARDUST produces puzzling results
The first in-situ chemical analysis of interstellar dust particles produces
a puzzling result: These cosmic particles consist mostly of 3-dimensionally
cross-linked organic macro-molecules, so-called polymeric-heterocyclic-
aromates. "They rather resemble tar-like substances than minerals" say Dr.
Franz R. Krueger (contractor) and Dr.Jochen Kissel, Max-Planck-Institut fur
extraterrestrische Physik (for extraterrestrial Physics), Garching near
Munich, Germany, in the latest issue of 'Sterne und Weltraum' a monthly,
German language Astronomy magazine in Heidelberg, Germany.
So far, 5 interstellar dust particles (dust between the stars) have hit
the Garching built dust impact mass spectrometer CIDA (Cometary and
Interstellar Dust Analyzer) onboard the NASA spacecraft STARDUST.
Launched on Feb 7th 1999 STARDUST will visit comet Wild-2 (pronounce
Vild-2) in 2004.
To reach the comet, STARDUST has to perform three orbits about the sun.
At the close fly-by (miss-distance 500 km/300 miles) another instrument
will collect cometary dust and return it, well packed, to earth in January
of 2006. During its 7 year mission, STARDUST will face the stream of
interstellar dust several times. This dust is part of the local environment
in the Milky Way which the solar system currently passes through at high
speed. It has recently be seen by dust instruments of the Heidelberg-based
Max-Planck-Institut fur Kernphysik (for Nuclear Physics) on both NASA's
Galileo and ESA's Ulysses spacecrafts. The first measuring campaign for
CIDA from February through December 1999 has produced the new results.
During this time STARDUST was at a distance of about 240 million
kilometers (150 million miles) from the earth when the first impact
occurred. Just before the campaign the spacecraft pointed the instrument
into the direction of the interstellar dust, so that it would not measure the
more frequent interplanetary dust particles, which are parts of our solar
At an impact speed of about 30 kilometers/second (18 miles/second) these
interstellar dust particles are vaporized immediately and broken up into
molecular fragments. A fraction of those carries a positive or negative
electronic charge. By its electric field in front of the target CIDA pulls the
positive ions into the instrument to the detector. Depending on their mass
it takes the ions different times to travel the 1.5 meters (5 feet) distance
(heavier ions travel longer). This way they are detected mass after mass
with in some 200 millionth of a second, and a mass spectrum is generated.
"It is the size of these molecular fragments with nuclear masses of up to
2000 (water e.g. has 18 such units) which surprised us as much as the
seemingly absence of any mineral constituents", explains Dr. Kissel of the
Garching-based Max-Planck-Institut fur extraterrestrische Physik. "Only
organic molecules can reach those sizes". The largest molecules found in
space so far are the polycyclic aromatic hydrocarbons (PAH) which reach
masses of a few hundred mass units.
The details of the mass spectra measured with CIDA show that the
molecules of the interstellar dust must have about 10% of nitrogen and/or
oxygen in addition to hydrogen and carbon. This means that these cannot be
pure PAHs, which are planar, but are especially due to the nitrogen extend
into all three spacial directions.
Such three dimensional molecules can form links to their neighbours and
reach a thermal stability necessary to survive the trip into the inner solar
system with 300 to 350 Kelvin (70 to 180 degrees Fahrenheit). "The organic
material analyzed with CIDA in the interstellar dust particles is another
type of reactive molecules which we found in the dust of comet Halley 14
years ago" says Dr. Kissel. "When they got in contact with liquid water on
the young earth, they could have triggered the type of chemical reactions
which are a prerequisite for the origin of life."
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