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GRAINS of cosmic dust coated with ice may have been the source of complex
organic molecules that kick-started life on Earth, according to astronomers who
have been studying data from a new infrared telescope.

Since last year, NASA鈥檚 Submillimeter Wave Astronomy Satellite (SWAS) has
been looking at infrared emissions from molecular clouds in interstellar space.
It鈥檚 the first telescope sensitive enough to examine the coldest regions of the
clouds.

One of the mission鈥檚 aims has been to look for water and molecular oxygen. To
the SWAS team鈥檚 surprise, molecular clouds at only a few kelvin contained less
than 1 per cent of the water and oxygen the astonomers expected to find
there.

鈥淲e are seeing water everywhere in space but here,鈥� says Ed Bergin of the
SWAS team at the Harvard-Smithsonian Center for Astrophysics in Cambridge,
Massachusetts. The low pressure in space normally means water is found as
vapour. But Bergin thinks that the reason they haven鈥檛 detected very much water
is that it has sublimed and frozen onto the surface of dust grains.

And ice-coated grains are also able to soak up oxygen from the cloud, say
Marco Spans at the Kapteyn Institute in Holland and Ewine van Dishoeck at Leiden
Observatory in Germany. 鈥淚ce-coated dust grains act as a sort of catalytic site,
where chemical species get adsorbed next to each other and can react,鈥� says
Bergin. This process helps form the complex organic molecules that scientists
think may have played a role in starting life when they fell to Earth inside
comets.