[meteorite-list] Is Life The Rule Or The Exception? The Answer May Be In The Interstellar Clouds

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:04:53 2004
Message-ID: <200205281519.IAA04888_at_zagami.jpl.nasa.gov>

ESA Science News
http://sci.esa.int

28 May 2002

Is life the rule or the exception? The answer may be in the
interstellar clouds

Is life a highly improbable event, or is it rather the inevitable
consequence of a rich chemical soup available everywhere in the cosmos?
Scientists have recently found new evidence that amino acids, the
'building-blocks' of life, can form not only in comets and asteroids,
but also in the interstellar space. This result is consistent with
(although of course does not prove) the theory that the main
ingredients for life came from outer space, and therefore that
chemical processes leading to life are likely to have occurred
elsewhere. This reinforces the interest in an already 'hot' research
field, astrochemistry. ESA's forthcoming missions Rosetta and Herschel
will provide a wealth of new information for this topic.

Amino acids are the 'bricks' of the proteins, and proteins are a type
of compound present in all living organisms. Amino acids have been
found in meteorites that have landed on Earth, but never in space. In
meteorites amino acids are generally thought to have been produced
soon after the formation of the Solar System, by the action of aqueous
fluids on comets and asteroids -- objects whose fragments became
today's meteorites. However, new results published recently in Nature
by two independent groups show evidence that amino acids can also
form in space.

Between stars there are huge clouds of gas and dust, the dust
consisting of tiny grains typically smaller than a millionth of a
millimetre. The teams reporting the new results, led by a United
States group and a European group, reproduced the physical steps
leading to the formation of these grains in the interstellar clouds
in their laboratories, and found that amino acids formed spontaneously
in the resulting artificial grains.

The researchers started with water and a variety of simple molecules
that are known to exist in the 'real' clouds, such as carbon
monoxide, carbon dioxide, ammonia and hydrogen cyanide. Although
these initial ingredients were not exactly the same in each
experiment, both groups 'cooked' them in a similar way. In specific
chambers in the laboratory they reproduced the common conditions of
temperature and pressure known to exist in interstellar clouds,
which is, by the way, quite different from our 'normal' conditions.
Interstellar clouds have a temperature of 260 C below zero, and the
pressure is also very low (almost zero). Great care was taken to
exclude contamination. As a result, grains analogous to those in the
clouds were formed.

The researchers illuminated the artificial grains with ultraviolet
radiation, a process that typically triggers chemical reactions
between molecules and that also happens naturally in the real
clouds. When they analysed the chemical composition of the grains,
they found that amino acids had formed. The United States team
detected glycine, alanine and serine, while the European team
listed up to 16 amino acids. The differences are not considered
relevant since they can be attributed to differences in the initial
ingredients. According to the authors, what is relevant is the
demonstration that amino acids can indeed form in space, as a
by-product of chemical processes that take place naturally in the
interstellar clouds of gas and dust.

Max P. Bernstein from the United States team points out that the gas
and dust in the interstellar clouds serve as 'raw material' to build
stars and planetary systems such as our own. These clouds "are
thousands of light years across; they are vast, ubiquitous, chemical
reactors. As the materials from which all stellar systems are made
pass through such clouds, amino acids should have been incorporated
into all other planetary systems, and thus been available for the
origin of life."

The view of life as a common event would therefore be favoured by
these results. However, many doubts remain. For example, can these
results really be a clue to what happened about four billion years
ago on the early Earth? Can researchers be truly confident that the
conditions they recreate are those in the interstellar space?

Guillermo M. Muņoz Caro from the European team writes "several
parameters still need to be better constrained (...) before a
reliable estimation on the extraterrestrial delivery of amino acids
to the early Earth can be made. To this end, in situ analysis of
cometary material will be performed in the near future by space
probes such as Rosetta ..."

The intention for ESA's spacecraft Rosetta is to provide key data
for this question. Rosetta, to be launched next year, will be the
first mission ever to orbit and land on a comet, namely Comet
46P/Wirtanen. Starting in 2011, Rosetta will have two years to
examine in deep detail the chemical composition of the comet.

As Rosetta's project scientist Gerhard Schwehm has stated, "Rosetta
will carry sophisticated payloads that will study the composition
of the dust and gas released from the comet's nucleus and help to
answer the question: did comets bring water and organics to Earth?"

If amino acids can also form in the space amid the stars, as the
new evidence suggests, research should also focus on the chemistry
in the interstellar space. This is exactly one of the main goals
of the astronomers preparing for ESA's space telescope Herschel.

Herschel, with its impressive mirror of 3.5 metres in diameter (the
largest of any imaging space telescope) is due to be launched in
2007. One of its strengths is that it will 'see' a kind of radiation
that has never been detected before. This radiation is far-infrared
and submillimetre light, precisely what you need to detect if you
are searching for complex chemical compounds such as the organic
molecules.

The results of the laboratory experiments were published in the 28
March issue of Nature:

* Amino acids from ultraviolet irradiation of interstellar ice
  analogues by G. M. Muņoz Caro (Leiden Observatory, The Netherlands)
  et al.
* Racemic amino acids from the ultraviolet photolysis of interstellar
  ice analogues by Max. P. Berstein (SETI Institute, United States)
  et al.

USEFUL LINKS FOR THIS STORY

* What is life, and how do we look for it?
  http://sci.esa.int/content/doc/55/30037_.htm
* Astrochemistry: the laboratory is in the stars
  http://sci.esa.int/content/doc/5c/30044_.htm
* More about Rosetta
  http://sci.esa.int/rosetta/
* More about Herschel
  http://sci.esa.int/herschel

IMAGE CAPTION:
[http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=30039&ooid=29964]
Did the main ingredients for life come from outer space? Amino acids,
the 'building blocks' of life, may form in dust grains in the space
between the stars.
Received on Tue 28 May 2002 11:19:12 AM PDT