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BBC Science's Richard Hollingham
The controversial theory holds that interstellar particles seeded the Earth
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Wednesday, 3 May, 2000, 16:35 GMT 17:35 UK
Organic molecules found in 'stardust'
Stardust will reach comet Wild-2 in 2004
By BBC News Online science editor Dr David Whitehouse

The first measurements of interstellar dust particles by Nasa's Stardust spacecraft suggest they are made of tar-like molecules that scientists believe could have played an important role in the origin of life on Earth.

The Cida collector
If confirmed, this discovery could mean that molecules drifting in space before our Earth was formed may have helped start life on our planet and by implication elsewhere in the Cosmos.

"When they got in contact with liquid water on the young Earth, they could have triggered the type of chemical reactions which are prerequisite for the origin of life," said Jochen Kissel, of the Max Planck Institut fur Extraterrestrische Physik, Germany.

So far, five interstellar dust particles have been captured by the German-built Cometary and Interstellar Dust Analyser (Cida), onboard the spacecraft.

Seven year voyage

Nasa's Stardust spacecraft was launched in February 1999. It will visit comet Wild-2 in 2004 and return samples from the comet, as well as interstellar dust, to Earth two years later.

To reach the comet, Stardust will circle the Sun three times. During its seven-year voyage through the Solar System, the spacecraft will encounter streams of interstellar dust several times.

The particles have an impact speed of about 30 km per second (18 miles per second) and on impact are broken up into molecular fragments. However, their original mass can still be estimated.

"It is the size of these molecular fragments, with nuclear masses of up to 2000 units (water has 18 units), which surprised us as much as the seeming absence of any mineral constituents," explains Dr Kissel.

Life in space

The apparent discovery that cosmic particles consist mostly of large and complex molecules could have far-reaching implications.

Only organic (carbon-based) molecules can reach these sizes, which are far larger than anything that has been found in space before.

The biggest molecules previously found in space are the polycyclic aromatic hydrocarbons, which reach a few hundred mass units.

It has been suggested that the molecular building blocks of life could be common in space and eventually land on a planet that by chance offers the right conditions for molecular evolution to take place.

The emergence of the simplest lifeforms may follow.

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See also:

23 Feb 00 | Sci/Tech
Spacecraft collects stardust
21 Mar 00 | Sci/Tech
ET gases caged on Earth
10 Mar 00 | Sci/Tech
Lunar rock reveals life's clues
16 Jul 99 | Sci/Tech
Rare form of carbon found in space
12 Apr 99 | Sci/Tech
Balloon bags space dust
19 Feb 99 | Sci/Tech
Kick-start for life on earth
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