Aliens, Penguins and Bacteria-Hunting Balloons
There’s a long history of astronomers looking for signs of life on Venus. Throughout the 19th century and into the 20th, reports circulated of a mysterious glow, known as the Ashen Light, which sporadically appeared on the planet’s night side. Could it be a product of civilisation, perhaps the glow of vast ritual bonfires breaking through the thick clouds that were known to blanket the planet? Later writers speculated about vast underground cities, or intelligent creatures who made the most of the thick atmosphere for aerial acrobatics.
When spacecraft finally visited our neighbouring planet, in the 1960s, dreams of life on Venus receded. A runaway version of the greenhouse effect has changed what may once have been a pleasant world to a decent approximation of hell; the surface temperature is hot enough to melt lead, the pressure on the ground high enough to crush a visiting astronaut, and those thick clouds are mostly sulphuric acid. A few dreamers still wrote of floating cities in Venusian clouds, but attention turned to Mars as the best bet for searching for past or present life.
Until this week, that is. On Monday, an international team of researchers announced the discovery of possible signs of life in Venus’s atmosphere. The team, led by Jane Greaves of Cardiff University, and using telescopes in Hawaii and Chile, had detected phosphine gas roughly thirty miles above the planet’s surface.
On Earth, phosphine is made only by life, either by human activity or by bacteria in the guts of some animals, including penguins (bringing great joy to the science writers of the world, now able to combine aliens and penguins in a single story). Calculations by Greaves et al. suggest that the amount of phosphine observed on Venus exceeds by a factor of 10,000 what could be produced by conventional chemistry, and may therefore be a byproduct of life.
If it is life, it must be very strange. At that height in the atmosphere the temperature (20 to 30°C) and pressure (roughly equal to that at sea level on Earth) are both relatively balmy, but there is still that acid to contend with. No earthly life could survive in these conditions: even our acid-loving bacteria would struggle. Yet their Venusian equivalents may be clinging on, tucked up inside water droplets in the clouds, the last remnant of a once rich ecosystem forced to adapt to a strange environment by a rapidly changing climate.
I’m not sure if this is a parable of ecological doom or a sign of hope. Life, as Jurassic Park put it, finds a way. In any case, the discovery of life on Venus would have profound implications. Our search for life in the cosmos could expand to a much richer and more imaginative set of circumstances than rocky planets that look like ours. And if it were to turn out that life got going independently on Venus, rather than by contamination via meteorite from Earth, then its presence would suggest that life is common throughout the Universe, and we should expect to explore a cosmos filled with biology. All sorts of magnificent worlds and unusual beasts would await, just as science fiction promises, even if mostly limited to the scale of micro-organisms.
There is much argument and follow-up work ahead. Telescope observations planned for earlier this year were delayed by the pandemic, and the chemistry of phosphine, a nasty, toxic chemical, is not well studied. But to really understand what’s going on, we will need to visit. Perhaps the Venusians, if they’re there, would welcome some company. A dirigible, carrying a chemical laboratory capable of testing directly for life, could float for months among the Venusian clouds, like something out of 19th-century science fiction. It may not have floating cities, but Venus may one day soon host a bacteria-hunting balloon.