For years now scientists have been looking for a reason to visit Venus. Why would anyone want to go there? Visiting Venus is like visiting your own car battery on the inside. Add some extras too. On Venus, the temperature is almost 500 degrees Celsius, and the pressure is 90 times the one on Earth. Your car battery is actually more forgiving, even though is still mostly sulphuric acid, just like the surface of Venus.
But some are very eager to take the trip. We are, right now, here on Earth, the only life we’ve ever known. Maybe we are not alone in the Universe? While that surely sounds like a ridiculous question, the probability of finding intelligent life elsewhere in the Solar System is nearing zero. In saying that, the hopes are that we might find other types of life, such as simple life, just like life on Earth was for over 3 billion years.
Why do we care so much about finding life elsewhere?
Because if we do, maybe we will not have to carry the burden of being so special. We could maybe instead carry on with wars and destruction. We would not have to worry about legacies and protecting our planet, recycling and making sure our species will survive. There will be others.
Or it may mean that we can finally get an answer to one of the mysteries of our existence. How did life start?
Or even better, how did life as we know it start? On early Earth, there was life, but not the kind breathing oxygen, that we take for granted. We begun with an oxygen free atmosphere. Some of the microbes that lived then, learned how to use sunlight to grow on carbon dioxide and water and gave off oxygen as waste. About three billion years ago oxygen reached 0.03 percent of today’s levels (Canfield, 2014). The first mass extinction that we know about happened when the byproduct oxygen was so abundant that it poisoned the other life forms. We are the descendants of the wicked ones.
How do we find life elsewhere?
We send robots if it’s near, such as our Solar System, or we look with the telescopes to see if we detect any biosignatures. While there is no universally accepted scheme for classifying biosignatures, there are three broad categories: gaseous, surface and temporal biosignatures. Gaseous biosignatures are products of the metabolism, such as detection of oxygen in the atmosphere of a planet, surface biosignatures occur when radiation is reflected or scattered by organisms on the surface of a body and temporal biosignatures are changes in the measurable quantities of a gas over time – for instance seasonal changes in CO2 on Earth as response to seasons (Schwieterman et al., 2018).
So far we sent rovers to Mars to look for life, other spacecraft to orbit planets and collect data from their atmospheres and we have ground-based and space-based observatories that are looking for biosignatures.
What is a biosignature?
In astrobiology, any “object, substance, and/or pattern whose origin specifically requires a biological agent” (Des Marais and Walter, 1999; Des Marais et al., 2008) is a biosignature. A gas can be a biosignature even though it might have nonbiological origins. For instance, we detect methane on Mars and its amount fluctuates with the seasons. But methane can be made both by living organisms or through geological processes. Sometimes these biosignatures can be ambiguous. What we hope to figure out is a biosignature whose presence definitely indicates there could be life out there.
Such biosignature is possibly phosphine, PH3. This gas is now considered a promising biosignature if detected in a rocky planet’s atmosphere. Phosphine has been found in the reducing atmospheres of Saturn and Jupiter as well. There it forms naturally in the core, under temperature and enormous pressure and is dredged upwards by convection. Rocky planets have solid surfaces which act as a barrier to their interiors. PH3 would be rapidly oxidised as it would go through the crust and atmosphere (Greaves et al, 2020). This means that any phosphine detected on the surface of a rocky planet would have to be made by something else on the planet – life (Sousa-Silva et al, 2019).
Phosphine is easy to detect, just like water or methane
PH3 can be detected in similar ways as we try to detect water or methane as it’s spectrally active in the same wavelength regions as the other atmospherically important molecules. This means it doesn’t cost extra to search for phosphine if you already search for water or methane. (Sousa-Silva et al, 2019).
On Earth, PH3 is associated with anaerobic ecosystems. The traces of phosphine in Earth’s atmosphere are definitely biological but we don’t yet know how microorganisms are making it on Earth (Matthew Pasek, NYTimes). Phosphine is a deadly gas for us, humans, which is probably why it has already been used as a chemical weapon.
On Venus, we think there is about a thousand times more phosphine than on Earth. And considering all the above, if it has really been detected on Venus, something must replenish it.
Venus, personification for the goddess of love, is a deadly place
It’s somewhat ironic that Mars, the planet named after the god of war and destruction, could be one day a new home for earthlings, yet Venus, named after the goddess of beauty, is such a deadly place. While most astrobiologists now obsess with searching for life on Mars, very few efforts have been made to look at Venus. It’s easy now to land a rover on Mars and keep it there in one piece. They send fabulous images back on Earth. When we look at these rovers from orbit, we even see them. There is no wonder then that Mars has an army of robots keeping it under surveillance.
Venus has thick clouds made of sulphuric acid that shroud the planet. We ‘see’ Venus in infrared and radio waves. The few spacecraft that landed on it have been squashed to death by the enormous pressure. Right now, one lonely spacecraft, the Japanese Akatsuki is orbiting Venus, although NASA’s Parker Solar Probe is using it for gravity assist manoeuvres and ESA’s Bepi Colombo, on its way to Mercury did the same.
But if you take Mars’s thin and cold atmosphere, which is 100 times thiner than Earth’s, and increase it by 9000 times, you get a Venus! European Space Agency (ESA)’s MarsExpress and VenusExpress looked at both planets and saw their atmospheres are made of 95% of carbon dioxide. The devil is in the detail, more precisely how much atmosphere is there.
The lure of Venus
Just like Uranus, Venus rotates from east to west. It has the longest day of any planet in the Solar System, which is 243 Earth days — even longer than a whole year on Venus. It could have had an ocean about a billion years ago (Livescience, 2019) and recent volcanism was detected on the surface of the planet (Filiberto et al, 2020). Since many years ago, it has been suggested that the clouds of Venus might be able to host life inside the clouds (Morowitz & Sagan, 1967). All these reasons are very compelling arguments to keep looking at the most beautiful and brilliant object in the night sky as seen from Earth.
The recent phosphate discovery on Venus is very enticing. The most defining aspect of life is the capacity for evolution, which is necessary to adapt organisms to changing environmental conditions. On Earth, life crawls and thrives in the most inhospitable conditions. If life ever existed on Venus, the most resilient and lucky microorganisms could have survived and adapted to living in the clouds.
Scientists, while very excited about their discovery, urge to consider further research and most label the results as promising but inconclusive. Which means nobody is yet convinced they discovered life on Venus, just phosphine. In the meantime, it looks like Jim Bridenstine at NASA will be gearing up to see what’s going on.