Although it is a hellish planet today, ancient Venus may have held seas of liquid water, and possibly, even life. What went wrong?
Venus is a world with an atmosphere of carbon dioxide so thick it would easily crush anyone foolhardy enough to stand on its surface. Sulfuric acid rain and temperatures hot enough to melt lead make this one of the least-habitable worlds in the Solar System. But, this world may once have harbored vast seas and potentially, life.
A new study suggests this planet may have once been a temperate world, far different than the one we see today. For two to three billion years, Venus may have been a water world, until a massive geological cataclysm around 700 million years ago changed the climate of that world forever.
“Our hypothesis is that Venus may have had a stable climate for billions of years. It is possible that the near-global resurfacing event is responsible for its transformation from an Earth-like climate to the hellish hot-house we see today,” said Michael Way of The Goddard Institute for Space Science.
That’s a Pioneering Spirit!
The first evidence of water on ancient Venus came from the Pioneer missions to Venus 40 years ago. Measurements obtained during this program suggested Venus may have once held on to a shallow ocean worth of liquid water before temperatures rose to blistering highs.
To test this four-decade-old idea, Way and his team created a series of five virtual simulations, showing what conditions would have been like on Venus, given varying concentrations of water. Each of these scenarios showed water could have remained stable on the surface of Venus for three billion years — more than enough time for life to develop and flourish.
Three of the five scenarios studied by researchers assumed a topography similar to that seen on Venus today, with oceans averaging 310 meters (1,000 feet), 10 meters (33 feet), and water locked in the Venusian crust. The fourth model measured planetary processes with an Earth-like topography and a 310-meter deep ocean, while the fifth scenario modeled Venus as a complete water world, with an ocean averaging 158 meters (~500 feet) in depth.
The circulation model used in the scenarios accounted for atmospheric changes on Venus, as well as the warming of the Sun, which releases more heat as it ages. Changes in the environment of Venus were examined from 4.2 billion years ago to 715 million years before our time.
This is Where Everything Goes Wrong
Then, roughly 700 million years ago, a massive outgassing released tremendous amounts of carbon dioxide into the atmosphere, creating a runaway greenhouse effect and altering the future of the planet. Temperatures that once hovered between 20 and 50 degrees Celsius (68 to 120 degrees Fahrenheit, typical temperatures in southern Arizona) soared to 465 C (870 F).
This tremendous, sudden heating may have been the result of volcanism. As massive deposits of solidified magma broke the surface of Venus, the event would have sent vast amounts of carbon dioxide back into the atmosphere. But, since this magma was already solid, it could not reabsorb the carbon dioxide released in the eruption. This gas created a runaway greenhouse effect on Venus, leading to the hellish environment we see today.
Although evidence provides strong evidence for this ancient cataclysm, the underlying reasons behind the volcanic eruption remains a question.
“[The Event] may be related to Large Igneous Provinces (LIPs) similar to (but much larger) than those we have had in Earth’s past and are linked to mass extinction events from extreme climate change like the Siberian Traps,” Way explains for The Cosmic Companion.
This eruption on Venus may have been triggered as the geology of Venus changed, altering the way the upper crust of Venus moved, creating the environmental catastrophe.
“Maybe these larger LIPs could have come about if the planet moved from an Earth-like subductive plate tectonics mode to a single lid plate tectonics mode as we see on Venus today,” Way continues.
In the era just before the extinction of the dinosaurs, massive volcanic eruptions of the Deccan Traps (in what is now India) could have led to one of the greatest extinctions in history, leading to the rise of mammals, and eventually, human beings.
Floating Other Notions of Life on Venus
Surface conditions on Venus are horrendous, but recent theories suggest that primitive life might exist high in the atmosphere of that alien world, where temperatures are more temperate.
“If Venus had surface liquid water and habitable conditions for 3 billion years then I don’t see why organisms could not have filled every ecological niche on Venus during that time, as they have on Earth over a similar period of time. Such niches could include life in the cloud tops of Venus,” Way tells The Cosmic Companion.
At altitudes around 50 kilometers (30 miles) above the surface of Venus, temperatures hover around 60 C (140 F), and atmospheric pressures are the same as at sea level on Earth, providing a potentially habitable layer within the atmosphere.
“[P]articles in Venus’ lower clouds contain sufficient mass balance to harbor microorganisms, water, and solutes, and potentially sufficient biomass to be detected by optical methods,” researchers report in the September 2018 issue of Astrobiology.
Although Venus is usually classified as being too close to the Sun for water to pool or life to form, this new study shows climatic conditions on Venus may once have been far more hospitable than they are today.
When the planet finished a period of rapid cooling 4.2 billion years ago, its atmosphere as dominated by carbon dioxide. If that world evolved as ours did, much of that gas would have been trapped in rocks, where it was locked away for more than three billion years. Prior to the environmental upheaval, the atmosphere on Venus was likely dominated by nitrogen and methane.
“Venus… Venus… the planet named after the Goddess of Love. This is where I left her… 26 million miles away. Because I know she exists. I know she does! I know it! …You may think I’m crazy back there on Earth. Crazy and still intoxicated by the atmosphere back there.” — Narrator, Voyage to the Planet of Prehistoric Women
At the time of the geological upheaval on Venus 700 million years ago, Earth was experiencing its own climatic challenges, as our world was caught in the greatest ice age it had ever seen, a period known as Sturtian glaciation, commonly called snowball Earth.
Confirmation of a terrestrial climate on Venus could come from several instruments, but none are currently funded.
Only a handful of spacecraft, all Soviet, have successfully landed on Venus, and none have last much longer than two hours before succumbing to the harsh environment. The last such craft to touch down on Venus, Venera 14, did so in 1982.
Roscosmos (the Russian space agency) and NASA are currently discussing plans for a joint robotic mission to Venus, Venera-D, designed to withstand the harsh conditions on the surface of that world for several months.
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