It remains one of the most unexpected scientific discoveries of the year. To their astonishment, British scientists last week revealed they had uncovered strong evidence that phosphine – a toxic, rancid gas produced by microbes – exists in the burning, acid-drenched atmosphere of Venus.
By rights, it should simply not be there. “All the geological and photochemical routes we can think of are far too underproductive to make the phosphine we have seen,” said Cardiff University astronomer Professor Jane Greaves, leader of the team who made the discovery. And that conclusion leaves scientists with the bizarre prospect that microbial activity – the key source of phosphine on Earth – may be occurring in the searing, acidic clouds that swathe Venus.
Not surprisingly, the news that there may be bugs on Venus made front-page headlines. It also adds a bizarre new planetary focus for scientists hunting alien life on nearby planets – a search that is now leading them to increasingly strange and unexpected parts of the solar system, from the frozen moons of Jupiter to the methane-filled lakes of Titan, the largest moon of Saturn.
While astronomers have yet to detect alien lifeforms, most are confident of success one day, though their journey will have taken them through some intriguing highs and some despairing lows. For example, in the late 19th century, and for much of the 20th, most astronomers were confident they would one day find life in the solar system.
And two worlds looked especially promising: Mars and Venus, our nearest planetary neighbours. Telescopes showed Venus was permanently shrouded in clouds – so it was assumed this was a world covered in steamy jungles filled with exotic animal life. At the same time, observations of Mars suggested seasonal changes in vegetation were occurring there with some astronomers arguing they could actually see signs of canals that had been constructed on the planet.
“Then, in the early 1960s, we sent our first space probes to the planets and discovered that Mars was a frozen, dead desert and that Venus was a hellhole,” said astrobiologist Lewis Dartnell, of the University of Westminster. “The prospects of finding alien life in the solar system took a nosedive.”
In the case of Mars, the planet was found to have a painfully thin atmosphere and was being battered by ultraviolet radiation, while Venus was revealed to have a dense, super-heated atmosphere of carbon dioxide lurking below thick clouds of sulphuric acid. The place was so hot, lead would melt on its surface. Astronomers’ hopes of finding alien life on worlds near Earth were crushed.
But in recent years, these hopes have started to rally. On Earth, carbon-based organisms called extremophiles have been found living in some extraordinarily hostile places: in nuclear waste; in highly acidic waters; in undersea vents where temperatures and pressures reach colossal levels; and on panels bolted to the outside of the international space station and exposed to the vacuum of space for years.
Life is not quite so fragile as was once supposed, it has been discovered. And if microbes could survive grim conditions on Earth, perhaps some could endure the harsh environments of Mars or other hostile parts of the solar system.
In addition, US interplanetary probes that began to explore the solar system’s remoter edges returned data that also raised hopes. Jupiter was found to possess moons that have deep underground oceans while Titan was discovered to have an atmosphere containing organic chemicals, the building blocks of life, and had lakes of hydrocarbons such as ethane and methane on its surface.
For good measure, when US space engineers did get around to sending new missions to Mars, these revealed ancient creeks and river beds through which water had once coursed freely. Perhaps, life had evolved on the red planet and may still be clinging on in underground pockets.
“It was a double whammy,” said Dartnell. “Planetary science expanded and found new possible homes of life while the biological sciences showed organisms could survive in much harsher environments than we had previously supposed. That has given astrobiologists like myself renewed hope we have a chance of finding life on other worlds in our solar system.”
These forms of life – if they exist at all – are definitely not going to be made up of intelligent beings capable of building canals or of animals that populate alien jungles, scientists stress. Most expect they will come in the form of fairly simple organisms. Nevertheless their discovery would have enormous repercussions.
At present, humans know of only one world that supports life:…