Podcaster: Fraser Cain
Title: Guide To Space – Venus Could Have Supported Life For Billions Of Years
Organization: Universe Today
Link: www.universetoday.com
Description: From Sep 24, 2019.
First Habitable Planet In The Solar System?
After decades of research, including multiple landers and orbiters, science can definitively say: Venus sucks. Seriously, that place is the worst, with its boiling temperature, intense pressure, sulfuric acid rain, and more.
But was it always this bad? According to new research from NASA and various universities in Sweden and the US, Venus might have actually been the first habitable world in the Solar System. And it might have maintained a reasonable climate for billions of years, finally rolling over into a runaway greenhouse effect just a few hundred million years ago.
Bio: Fraser Cain is the publisher of Universe Today
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Transcript:
After decades of research, including multiple landers and orbiters, science can definitively say, Venus sucks. Seriously, that place is the worst, with its boiling temperature, intense pressure, sulfuric acid, rain, and more. But was it always this bad?
According to new research from NASA and various universities in Sweden and the US, Venus might have actually been the first habitable world in the Solar System, and it might have maintained a reasonable climate for billions of years, finally rolling over into a runaway greenhouse effect just a few hundred million years ago. Today, Venus is a different story. Although the planet is roughly the same size and mass as Earth, it has a dramatically different environment.
The average global surface temperature is about 475 degrees Celsius, hot enough, as I’m sure you’ve heard, to melt lead. The atmospheric pressure on the surface of Venus is 90 times the pressure of Earth. Want to experience the same kind of pressure?
Dive down 1 km under the ocean and you’ll get an idea. How do we know? The Venera Program.
The Soviet Union sent a fleet of spacecraft in the 70s and 80s to try and land on the surface of Venus. 18 were sent, 13 actually made it into the atmosphere, and 10 survived all the way down to the surface, able to send back some data to Earth before they expired in the brutal environment. But we’re looking at Venus 4.5 billion years after its formation with the rest of the Solar System. And over those eons, the Sun has been heating up, Venus has been getting dried out, and many planetoids and asteroids have been smashing into each other. But if we roll the clock back, when could Venus have been habitable, and for how long? A new paper entitled, Was Venus the first habitable world of our Solar System?
was released in August 2019, in attempts to give us a glimpse into the Venusian past. It was written by Dr. Michael Way from NASA’s Goddard Institute for Space Studies, as well as researchers from Sweden, New York, Arizona, and Maryland. According to the study, Venus probably started out with a similar overall composition to Earth, including the same amounts of water and gases in its atmosphere.
Today, of course, it’s bone dry, with a mere 6 quadrillion kilograms of water in its atmosphere. Now, I know 6 quadrillion sounds like a lot, and it is, but Earth has more than 200,000 times as much water in its oceans and atmosphere. Astronomers were able to calculate how much water it used to have based on the ratio between deuterium and hydrogen in its atmosphere, and this indicates that it must have had much more in the ancient past.
Even though Earth’s atmosphere is 78% nitrogen, Venus actually has double that amount, and of course, an insane amount of carbon dioxide. Planetary scientists have calculated that ancient Venus had shallow seas across its surface, measuring from 4 to 525 meters deep. The question is, how much did it have, and how quickly did it lose its water?
The traditionally accepted answer was that Venus lost its water quickly, within the first 100 million years or so. Dr. Wayne and his team used Goddard’s ROC 3D simulator that I mentioned in the previous episode to simulate an ancient Venus with shallow oceans and an Earth-like atmosphere. They worked with a few assumptions.
The first is the length of a day on Venus. Today, the planet takes 116 days to turn on its axis. You could walk faster than Venus turns.
Not only that, but the planet is rotating backward from the other worlds of the Solar System. It’s possible that Venus was smashed by a massive planetoid early on in its history, but it’s also just possible that tidal interactions with the Sun slowed down its rotation rate almost immediately, and it’s been rotating this slowly ever since. They had to consider the surface of ancient Venus, which is actually a total mystery.
That’s because the entire landscape was completely resurfaced just a few hundred million years ago, as if the planet turned itself inside out. It’s believed this happened because Venus doesn’t have plate tectonics like Earth. Instead of regular volcanism releasing heat and pressure, the planet resurfaced itself in a catastrophic event.
So they based their models on the current surface features of Venus, as mapped out by NASA’s Magellan spacecraft. They filled the lowlands with water, assuming an early ocean that was about one-tenth the volume of Earth’s oceans. And they assumed that early Venus had an atmosphere as thick as Earth, but made almost entirely of nitrogen, with trace amounts of carbon dioxide and methane like Earth.
And then they just ran the clock forward, watching how the planet changed over billions of years as the Sun heated up and Venus dried out. What did they discover? We’ll get to that in a second, but first I’d like to thank Roman Brendel, Matthew Nichols, VengefulSorrow, Paul Wheeler, and the rest of our 825 patrons for their generous support.
Educational content should be freely available to anyone in the world, and the patrons make this possible. Join our community at patreon.com slash universe today and get in on the action. The team performed 5 simulations, based on different amounts of water coverage.
Three of the scenarios assumed a deep ocean, with an average of 310 meters. One scenario used the Earth’s topography, and a 310 meter deep average ocean. They also tried a scenario where all of Venus was covered by water, 158 meters deep.
They simulated the planet at 4.2 billion years ago, 715 million years ago, and today, watching as the amount of radiation coming from the Sun increased over time. Today, Venus receives twice as much solar radiation per square meter as Earth does. In all five scenarios, they found that Venus was able to maintain stable temperatures, ranging from a maximum temperature of 50 Celsius to a minimum of 20 Celsius.
And it kept these stable temperatures for almost 3 billion years. In the beginning, the planet had an incredibly thick atmosphere of carbon dioxide. But as it cooled down over the next 3 billion years, this carbon would have been drawn out of the atmosphere and locked away into silicate rocks.
By 715 million years ago, the planet would have had that one atmosphere of nitrogen and other trace gases. In fact, it could have remained stable, with liquid water on its surface, all the way until today. But some dramatic event happened hundreds of millions of years ago that transformed the planet forever.
And it might have been linked to that volcanic resurfacing that I mentioned earlier. In fact, Earth had a similar situation about 250 million years ago, when the largest volcanic eruption in our planet’s history covered an enormous amount of Siberia. The eruptions carried on for 2 million years, and led to one of the greatest mass extinctions in our planet’s history.
So that, but worse, and Venus never recovered, with the extreme heat from the molten rock releasing all that absorbed carbon dioxide into the atmosphere and leading to a runaway greenhouse effect. These simulations depend on the fact that Venus cooled down and was able to condense water onto its surface to form these global oceans, and they assume that this volcanic resurfacing happened just once, recently, and wasn’t a regular occurrence on Venus. It’s incredible to think that Venus could have been habitable for billions of years, and if it wasn’t for that catastrophic resurfacing, it might still be habitable today.
In order to get to the bottom of this mystery, we need to return to Venus with new orbiters, balloons to study its atmosphere, and even rovers and landers made of tough new heat-tolerant electronics to explore its surface. Unfortunately, there are no missions at Venus anymore, and a few are planned in the near future, so the mysterious history of Venus will have to remain that way for a few more years. And we will see all of you next week.
Thanks everyone!
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365 Days of Astronomy
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