The virus believed to cause Severe Acute Respiratory Syndrome (Sars) may have come to Earth from outer space, according to scientists writing in a leading British medical journal.
By Richard Black
BBC science correspondent
In a letter to The Lancet, the scientists, led by Professor Chandra Wickramasinghe of Britain's Cardiff University, say the Sars coronavirus is so unlike other viruses that an extra-terrestrial origin is logical.
However, a number of Sars experts believe the theory itself seems to have come from another planet.
The theory has been met with ridicule and disbelief by some
The idea that Sars comes from the stars relates to a theory called panspermia. This says that life itself evolved somewhere out in the cosmos, and is carried from one planet to another on comets.
Professor Wickramasinghe, who is a leading panspermia enthusiast, says the Sars coronavirus is so unusual that it could not have arisen on Earth.
"The particular genetic sequences of this Sars virus appears to be dramatically different from all the other known coronaviruses; and that has suggested an independent evolution of that virus to be required."
In other words, the virus evolved somewhere else, perhaps on another planet, before coming to Earth.
Professor Wickramasinghe admits there is no hard evidence for his theory; and researchers who have been working on Sars reacted with a mixture of disbelief and ridicule.
There is nothing strange about the Sars coronavirus, they said; it certainly evolved from other known viruses.
One leading expert said Professor Wickramasinghe's letter "must be a joke"; another said it was simply ridiculous.
And a spokesman for the World Health Organization re-assured me that they had no plans to send Sars inspection teams into outer space just yet.