In addition to searching for extraterrestrial
life, we pursue the search for
extraterrestrial life-related molecules
in order to establish the universal nature
of prebiotic chemical synthesis.
Recent discoveries show that comets,
which seem to have remained unchanged
since the formation of the
solar system, may represent a unique
storehouse of information about organic
synthesis at the time of formation.
We now have evidence that the
organic molecules believed to be precursors
of molecules essential for life
are prevalent in comets. These discoveries
have provided further support
for the view that chemical evolution
has occurred widely beyond the
Earth. Comets may even have played
a major role in the organic chemical
evolution of the primitive Earth itself.
Significant amounts of important precursor
molecules could have been
deposited on the primitive Earth by
Meteorites, which provide us with
solid samples of extraterrestrial material,
represent another source of information
about the occurrence of
prebiotic chemistry beyond the Earth.
In 1969, meteorite analyses provided
the first convincing proof for the existence
of extraterrestrial amino acids, a
group of molecules necessary for life.
Since then, a large body of information
has accumulated to show that many
more of the molecules necessary for
life are also present in meteorites, and
it now seems clear that the chemistry
of life is not unique to the Earth.
Future studies of meteorites should
greatly contribute to the eventual understanding
of the conditions and
processes during the formation of the
solar system and should provide clues
to the relations between the origin of
the solar system and the origin of life.
Clue in a cosmic mystery.
A fragment of the Murchison meteorite,
which fell on Australia in 1969. Organic matter of a type not produced
biologically was found in the meteorite.
The atmospheres of the outer gas
giant planets (Jupiter, Saturn, Uranus
and Neptune) represent yet another
extraterrestrial environment in which
prebiotic chemistry can occur. In fact
from our knowledge of the composition
of Jupiter's atmosphere, many
scientists consider it to be a good
model for the primordial atmosphere
of the Earth. Jupiter's atmosphere
contains the same gases (hydrogen,
methane, ammonia) that may have
been present when the Earth's atmosphere
formed, and violent lightning
flashes were detected in Jupiter's
clouds by the Voyager spacecraft.
With its abundant organic molecules
and electrical energy, Jupiter may be
the site of extensive prebiotic chemical
reactions that reproduce what
occurred on our own planet 4 to 4.5
billion years ago. We expect that further
important information on this
question will be provided by the
Galileo spacecraft as it makes direct
analyses of the turbulent atmosphere
of this giant gaseous world.