In mediaeval Europe there was a nasty fairy known as "Will-o'-the-wisp", who tempted unwise travellers to a watery doom in swamps.
He manifested himself as flickering, greenish flames. Of course, there is a more prosaic explanation. Phosphine gas was being generated by rotting material in the oxygen-free mud at the bottom of the swamp. That bubbled to the surface and burned in the air, producing greenish flames.
As far as we know, the only natural sources of phosphine are biological, such as rotting vegetation and unwise travellers. It would therefore be one of the last things we would expect to detect in the atmosphere of Venus.
Venus is probably the least likely place in the Solar System to invest in expensive space missions to seek life. The surface temperature is high enough to melt lead and tin and the atmospheric pressure is around 90 times as high as it is at sea level on Earth.
Apart from containing little or no oxygen, there are also corrosive drops of sulphuric acid blowing around in the Venusian atmosphere. Spacecraft have landed on the planet's surface. They lasted less than 30 minutes.
How, therefore, could astronomers have detected phosphine in that planet's atmosphere?
One possibility is the phosphine is produced by life forms high in Venus' atmosphere. Maybe paradoxically, the pressure and temperature around 50 kilometres above the surface are nearly the same as they are on the surface of the Earth. However, the atmosphere is different, being mainly carbon dioxide, nitrogen and a mixture of other chemicals, including hydrogen chloride, hydrogen fluoride and sulphur dioxide, along with droplets of sulphuric acid.
It is true that we could not survive in it, but there are creatures here on Earth that live in environments that are even more hostile, such as almost boiling, acidic pools of volcanically-heated water, and around the black smokers on the floors of our deep oceans.
The question is whether there is some sort of workable biological chemistry that possibly could evolve to use the available ingredients and energy supplies?
That makes Venus's atmosphere a more suitable place for life than anywhere else we know of in the Solar System, including the surface of Mars.
The "signal" from Venus's phosphine is weak, and there is an animated discussion going on as to whether it is real. Examination of older data from spacecraft shows evidence of phosphine, but not much of it. However, this possibility is the strongest suggestion of the presence of life beyond the Earth that we have found so far, which is why two space missions are being planned to have a much closer look.
One of them would involve sending a probe that would, under a parachute, drop slowly through the atmosphere, making measurements as it falls, and transmitting back to us what it is finding. It would end up frying on the surface, hopefully mission accomplished.
The second is more ambitious. It would involve deploying an instrument package supported by a balloon, hanging in Venus's atmosphere at the height of greatest interest, recording data about its surroundings and linking it back to us. One version of this project involves taking samples of the atmosphere and then, using a rocket attached to the package, sending those samples back to us on Earth so we can study them directly.
Venus is one of the places in the Solar System where manned missions are highly unlikely for the foreseeable future. The conditions are too hostile.
There’s no doubt we could develop technologies to make a visit possible, but would the challenge be worth the cost and risk?
The first footprints we make beyond the Moon will probably be on Mars. Hopefully we won't tread on something alive.
• Saturn lies in the south after sunset, with Jupiter shining in the east.
• Venus rises in the early hours.
• The Moon will reach its last quarter on Nov. 5.
This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.