In a laboratory in Nottingham, scientists are now creating the uniquely
harsh conditions encountered in interstellar space. In an environment where
the pressure is only one ten billion billionth (one part in 10 to the power
13) of atmospheric pressure, and the temperature a mere 10 degrees above
absolute zero, Dr Martin McCoustra and his colleagues are able to mimic the
surfaces of the ice-coated dust grains in interstellar clouds and to study
the complex chemical and physical processes that take place there. On
Tuesday 9 April Dr McCoustra will tell the National Astronomy Meeting in
Bristol why his team’s novel experiments are having far-reaching
consequences for understanding the way stars and planets form.

Stars and their planetary systems form in cold, dark clouds of gas and dust
that occupy the vast regions between the stars in our own and other
galaxies. Radio, millimetre-wave and infrared observations have revealed
that they are a ‘soup’ of over 110 different chemicals, some with molecules
made of 10 or more atoms. It is clear that complex chemistry is taking place
and the key to the chemical origins of life itself might lie in these
clouds. For certain, the chemistry controls the way regions in interstellar
clouds collapse under their own weight to create the precursors of stars.

Interstellar dust grains play a crucial role in the creation of the rich
variety of interstellar molecules and in the process of star formation, even
though they account for only 1% of the mass of a typical cloud. About the
same size as a fine particles of cigarette smoke, grains are made of
silicate minerals and carbon-based materials coated with ice – principally
water ice and frozen carbon monoxide.

But what’s the link between the grains and the star formation process? Dr
McCoustra explains, “When a star is trying to form, it gets hotter and
hotter as more gas collapses in on itself. There comes a point when the gas
is so hot it could expand out again as fast as it falls in. But if some of
the heat is radiated away, collapse can continue and a star can actually
form. It’s hot gas molecules that act as the radiators and the icy mantles
of the interstellar grains are the main reservoirs where the gas molecules
can come from. We need to understand exactly how the ice gets onto the
grains and evaporates from it again so that astrophysicists can accurately
simulate the process of star formation with computer models.

In recent experiments, the Nottingham team have studied how, under
interstellar conditions, water ice is released from grains, and the
interaction between carbon monoxide and the surface of frozen water. “We
have shown that the crude picture of each substance evaporating separately
at some theoretical temperature is wrong,” says Dr McCoustra. “Our
measurements indicate that a higher temperature than expected is needed to
evaporate water ice, and the combined water/carbon monoxide (CO) system is
much more complex. The water ice acts like a sponge, trapping the CO in
pores. This trapped CO is not released as a gas until all the water has

“Until recently, processes of this kind have been very poorly understood,”
adds Dr McCoustra, “but now we are seeing a revolution in what we can
achieve. Ultrahigh vacuum and surface science techniques in the laboratory
have given us the tools we need to probe the workings of an interstellar
cloud. Our unique surface astrophysics experiment is contributing to a
fundamental appreciation of the interactions between the gas and dust grains
that pervade much of the space between the stars.”

RAS Web site:

UK National Astronomy Meeting Web site:

Dr Jacqueline Mitton
Phone: +44 (0)1223-564914    Fax:    +44 (0)1223-572892
E-mail:  Mobile phone: 07770-386133

Peter Bond
Phone: +44 (0)1483-268672      Fax:    +44 (0)1483-274047
E-mail:    Mobile phone: 07711-213486

National Astronomy Meeting Press Room phones:
+44 (0)117 928-4337, (0)117 928-4338, (0)117 954-5913, (0)117 928-7901

Dr Martin R. S. McCoustra, School of Chemistry, University of Nottingham,
Tel:+44(0)115 951 3568    Fax:+44(0)115 951 3562