Venus, the second planet from the Sun, presents modern astronomers with a strange dichotomy; the surface is a smouldering, poisonous desert, yet the world above the clouds is the most Earth-like place in the Solar System.
At a distance of 50km above the Venusian soil, a position that correlates with the very edge of the stratosphere on Earth, pressure is a familiar 1 bar and temperatures range from 0-50°C.
However, amid such pervasive hostility (the pressure on Venus’ surface is 92 bars, while temperatures can reach a fiery 467°C), even the oases in the sky present problems for life.
Earth’s twin suffers beneath a hail of sulphuric acid, and the wind speed at such altitudes can exceed 210mph; any object travelling on the breeze would circle the planet in just four days.
So, what, if anything, would want to live on – or above – Venus’ surface? The obvious answer is scientists.
- Surviving the Storm
Human colonisation of Venus’ sky was first suggested by NASA’s Geoffrey Landis, who described the atmosphere of the Beige Planet as a “paradise” for specialised vessels.
Colonies of scientists – and perhaps, residential communities – could ostensibly survive floating beneath giant ‘hot air balloons’, drifting on the wind.
With breathing apparatus and protection from the deleterious weather, colonists could even venture outside.
Making matters easier, the mixture of oxygen and nitrogen that mammals and birds breathe on Earth would float on Venus, in much the same way as helium is a lifting gas on our own planet. One would simply need to find a balloon hardy enough to weather the acid rain storms.
“If you could just take the room you’re sitting in and replace the walls with something thinner, the room would float on Venus,” Landis told Universe Today.
While Landis’ theory is likely to remain in the realm of conjecture for a long time – he moonlights as a science fiction author – his ideas nevertheless raise an interesting point; if there is a place on Venus that has the potential to support life, has it already evolved to fill the niche?
- The Inferno
The conditions on the surface of Venus are hot enough to melt lead and tin, and to vaporise mercury; water particles cannot form within 22 miles of the surface.
To put those numbers into perspective, the Russian space probe, Venera 7, lasted 23 minutes on Venus before succumbing to the elements; her sister craft, Venera 8, lasted a marathon 50 minutes.
However, Venus was not always so hostile. Billions of years ago, the planet’s lowlands may have held liquid water. At the same time, the Earth’s surface may have choked beneath a smog of poisonous gases.
Our planet was saved by virtue of its aquatic lifeforms, which turned carbon dioxide into limestone. Venus, orbiting 30% closer to our parent star, had its oceans boiled away, the resultant water vapour creating the planet’s now-trademark greenhouse effect.
So, what of Venusian life? The great assumption here is, of course, that life evolved on (or was delivered to) the planet in the first place.
- Bears in Space
Let’s say it did. Scientists have envisioned a scenario in which Venusian microbes may have slowly developed resistances to acidity and heat, and found a new habitat in the relative calm of the clouds. The concept is not an unusual one; bacteria on Earth are capable of living and reproducing in the realm of birds and aeroplanes.
Equally, some microbes have evolved to thrive in brutally tough conditions – extremophiles, the most famous of which is the tardigrade or ‘water bear’. This tiny (<1mm) creature can live in the vacuum of space for 10 days, go a decade without food, endure massive doses of radiation, and live at temperatures near absolute zero.
In comparison, the balmy avenues in Venus’ upper atmosphere are about as conducive to life as one can get.
Despite the occasional similarity, Venus remains very different to Earth. A microbe subsisting in the Venusian sky would need a resistance to two dangerous elements, sulphur and ultra-violet (UV) radiation – or a way of using them to their advantage.
Environmental scientists – specifically, Dirk Schulze-Makuch, of the University of Texas – have postulated that Venusian bacteria could use one element to protect themselves against the other, forming a protective ‘sunscreen’ against UV with sulphur compounds.
Alternatively, bacteria could evolve to ‘eat’ radiation, similar to how plants on Earth derive their energy from visible light, a process known as photosynthesis. There is some debate over the peculiar absence of UV (and the unique formations of sulphor) in certain regions of Venus’ atmosphere.
But, once again, for the above to be anything more than a thought experiment, life on Venus must have survived the original warming episode. Whether life could take hold now – via panspermia, for example – in one of the most hostile locations in the Solar System, is debatable.