Venus may be one of the brightest and most beautiful objects in our night sky, but don’t be fooled.
Our neighboring planet is inhospitable to life as we know it – a toxic, scorching world that humans would never be able to walk in.
Despite the differences in habitability, Venus shares some striking similarities with Earth. Both planets are the same size, mass, and density, and have very similar compositions. This raises the question: could Venus ever be habitable?
A new study finds that if Venus had habitable conditions and the presence of liquid water on its surface, it was a long time ago, and only lasted for a brief period before the planet turned into the parched, dry world it is today.
Planetary scientists Alexandra Warren and Edwin Kite of the University of Chicago modeled the history of Venus’ atmosphere to determine the rate and mechanisms of oxygen loss – which in turn revealed that if the planet had liquid water (which some scientists suspect), it was more than 3 billion years ago.
This is what Venus looks like now. It is very dry and very low in oxygen. Its atmosphere is made up of 96 percent carbon dioxide, 3 percent nitrogen, with trace amounts of other gases, such as sulfur dioxide.
And because its atmosphere is so thick, heat cannot escape. Venus has the highest surface temperature of any planet in the solar system, on average 464 degrees Celsius (867 degrees Fahrenheit).
Earlier in the history of the solar system, when the Sun was less powerful, Venus may have been much milder, with lakes and oceans of liquid water.
Planetary scientists want to know how and why Venus got its current state; Because Venus is so much like Earth – some climate models suggest that Venus could have had water recently Less than a billion years ago – Working on its history can help us see how likely our home planet is to follow the same path.
The lack of oxygen in the atmosphere of Venus is a bit puzzling. If the planet had a liquid ocean, that water would have evaporated into the atmosphere as Venus heated up, breaking down into hydrogen and oxygen via photodissociationA chemical reaction caused by sunlight.
The hydrogen would have escaped into space, but the oxygen should have remained.
Warren and Kate wanted to know where that oxygen could go, so they built a model based on habitable Venus. They put water oceans on Venus, added mechanisms that could have contributed to the loss of oxygen, and modified parameters such as the amount of water, and the time frame in which it would have been present.
They let the model run 94,080 times, deeming it successful if levels of dioxygen, water and carbon monoxide were at the end of the race within the upper limits of those gases in Venus’ atmosphere today.
In the end, only a small percentage of model runs were successful, and it showed some interesting trends.
One possibility is that Venus’s oxygen became bound with carbon emitted by volcanoes to form carbon dioxide, but this seems highly unlikely.
Instead, the oxygen appears likely to suffer one of two fates: leaking out into space, or being locked into oxidizable magma, such as basalt, at the planet’s surface. The oceans must not have dried up in more than 3 billion years.
But the extent of Venus’s past volcanic activity can be constrained by the amount of radioactive argon still present in the planet’s atmosphere. By determining how active Venus’s volcanic activity was in the past, the researchers were able to estimate how much water the planet might have.
The answer is not sufficient. The oceans of Venus cannot be more than 300 meters (984 ft) deep. That’s less than 10% of the planet’s average 3688 meters ocean depth.
So the findings reconcile the lack of oxygen in Venus’ current atmosphere with early habitable conditions, but the gap, the researchers say, is narrow.
This gap becomes narrower when considering the argon register. Less than 0.4 percent of runs were successful when the full extent of Venus’ current atmosphere is taken into account.
Future missions could attempt to measure the composition of Venus’s surface to help determine if the planet really fell into this very narrow gap.
Research published in Proceedings of the National Academy of Sciences.
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