(Originally published in the Las Cruces Sun News on November 1, 2020 – link)
Up for a fun challenge? Make a list of planets and moons in our solar system where life could survive. Mars? Well, Mars does have subsurface water permafrost, polar water-ice caps, and geologic scars from ancient rivers and a water ocean that once covered half the planet. Europa? Warmed by Jupiter’s tidal forces, this moon has a frozen ice tundra surface that is episodically flooded by its underground ocean, which contains more water than Earth. Titan? This Saturnian moon boasts the solar system’s thickest atmosphere and huge liquid methane lakes that dwarf North America’s Great Lakes. Venus? I’m betting Venus didn’t make your list. Why? Well, perhaps because its surface is hot enough to melt lead, or its atmospheric pressure can crush a deep-sea submarine like a fragile egg, or that Venusian rain is sulphuric acid. Roughly 700 million years ago, Earth’s twin suffered a runaway global warming event and today is an acidic netherworld.
Newsflash: Astronomers may have just detected signs of alien life on Venus!
There are three big questions here. What exactly was detected? Why does it suggest life? And, what kind of life could thrive on that literal acid-bath inferno of a planet?
British professor Jane Greaves and her colleagues recently announced evidence for the molecule phosphine in the upper Venusian atmosphere. Phosphine is a lone phosphorous atom bonded to three hydrogen atoms. On Earth, phosphine is produced in abundance by microbes; only trace amounts come from non-biological processes. Years ago, when astronomers found phosphine in Jupiter’s and Saturn’s atmospheres, they did not trumpet “life on Jupiter!”. That is because they found non-biological explanations. So, why is Venus different?
The amount of Venusian phosphine Greaves and her team found was vastly greater than can be explained by non-biological mechanisms. You might get phosphine from lightning strikes or by cosmic rays hitting the upper atmosphere, but these small amounts are destroyed as rapidly as they are created. Something on Venus is making phosphine faster than it can be destroyed- ten thousand to a million times faster. Either there is some yet unknown non-biological process producing this phosphine, or Venus has phosphine producing life.
What could that life look like? Even though the Venusian surface is hellish, at around 30 miles altitude both the temperature and pressure approach those at Earth’s surface. In 1967, Carl Sagan and Harold Morowitz suggested that microbes or even jellyfish sized “alien floaters” might live permanently aloft in the Venusian upper atmosphere. Perhaps, but conditions for survival in the upper cloud deck of Venus are uncompromising. First, any lifecycle would be restricted to remaining aloft in a Goldilocks zone with survivable temperatures and pressures. Second, the little beasties would need to survive brutal acidity.
Professor Sara Seager from the Massachusetts Institute of Technology and her collaborators recently proposed that Venusian microbes may be living in tiny, floating, atmospheric droplets, which would be 85% hydrochloric acid and 15% water. These droplets form naturally at a narrow range of altitude. As they coalesce and grow, they fall into the blistering and crushing oven of the lower atmosphere where they evaporate. This is where our Venusian microbes show their resilience. Free floating and exposed, they would virtually shut down all life functions until they are buoyantly carried upward in the atmosphere where the tiny acidy water drops abound. Reunited and safely embedded in their acidic droplets, the microbes reactivate, reproduce, and… emit phosphine.
This scenario is no stretch of imagination. Earth’s microscopic tardigrades and endospores, when confronted with no water or the vacuum of space, enter a semi-permanent state called cryptobiosis. At will, they can awaken and thrive even after decades of self-protective hibernation. Some microbes thrive in 700-degree geothermal acid-rich fluid spewing into the black, sunless, crushing pressure abyss of the ocean floors. In 2014, French researchers Chantal Abergel and Jean-Michael Claverie uncovered a new strain of virus that laid dormant 30,000 years until the Siberian permafrost thawed and receded. Countless more are expected to reenter our biosphere in the coming century, resurrected by our warming climate. In 2018, Canadian graduate student Yana Eglit discovered an entirely new life form that comprises a new, fourth major branch on the tree of life; she named it Hemimastix Kukwesjijk (greedy, hairy ogre). As we learn more about life’s amazing strategies of adaptability, why should we be skeptical that biology is more diverse and resilient than we presently can imagine? One thing is for sure- in the near future, expect Venusian microbes, if they exist, to have a robotic close encounter courtesy of some curious Earthlings.
Dr. Chris Churchill is Professor of Astronomy at New Mexico State University. He can be reached at firstname.lastname@example.org
For additional information, see: https://www.eso.org/public/news/eso2015/