Venus Used to Have Oceans But Where Did the Water Go?

Its atmosphere has 10,000 to 100,000 times less water than Earth’s.

Electric wind. It sounds like the name of an indie, electro-industrial musical group. But it is something way cooler (at least in my opinion). According to a recent paper published in Geophysical Research Letters, electric wind might explain where Venus’ water went.

Scientists believe that every planet with an atmosphere is surrounded by a weak electric field. And the electric force can sometimes push the upper layers of the atmosphere into space, despite the planet’s gravity, which usually keeps the atmosphere in place. Unfortunately for our neighbor Venus, its electric field is so strong that any water molecule that rises into the upper atmosphere will be broken into hydrogen and oxygen ions, which are then carried away by the electric field.

"It's amazing, shocking," Glyn Collinson, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland and lead author of the paper, said in a NASA news release. "We never dreamt an electric wind could be so powerful that it can suck oxygen right out of an atmosphere into space."

Of our solar system, Venus is probably the most Earth-like in terms of its size and gravity. There is also evidence that it once had oceans of water. However, with the planet’s runaway greenhouse effect and surface temperatures reaching a balmy 460 degrees Celsius (860 degrees Fahrenheit), those oceans boiled away long ago.

^{Graphic comparing surface temperatures and gravity on Earth and Venus. Photo credit: NASA/Goddard/Conceptual Image Lab, Brian Monroe}

Bizarrely, Venus’ thick atmosphere, which is about 100 times the pressure of Earth’s, has 10,000 to 100,000 times less water than Earth’s atmosphere. Where did all the water go?

"We found that the electric wind, which people thought was just one small cog in a big machine, is in fact this big monster that's capable of sucking the water from Venus by itself," said Collinson.

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"If you were unfortunate enough to be an oxygen ion in the upper atmosphere of Venus then you have won a terrible, terrible lottery," continued Collinson, "You and all your ion friends will be dragged off kicking and screaming into space by an invisible hand, and nothing can save you."

Venus’ electric field was discovered while monitoring electrons flowing out of the planet’s upper atmosphere using the electron spectrometer aboard the European Space Agency’s Venus Express. Scientists noticed that the electrons were not escaping the planet at their expected speeds. The electrons were actually being tugged by Venus’ electric field, which was found to be five times more powerful than Earth’s.

^{Graphic comparing the atmospheric composition and electric field strength on Earth and Venus. Photo credit: NASA/Goddard/Conceptual Image Lab, Brian Monroe}

"We don't really know why it is so much stronger at Venus than Earth," said Collinson, "But, we think it might have something to do with Venus being closer to the sun, and the ultraviolet sunlight being twice as bright. It's a challenging thing to measure and even at Earth to date all we have are upper limits on how strong it might be."

Astronomers can also use electric winds to get better estimates of the size and location of habitable zones around other stars. "Even a weak electric wind could still play a role in water and atmospheric loss at any planet," said Alex Glocer of NASA Goddard, and co-author of the paper. "It could act like a conveyor belt, moving ions higher in the ionosphere where other effects from the solar wind could carry them away."

Since humans are dead set on colonizing our other planetary neighbor, Mars, scientists are "actively hunting for Mars' electric wind," said Collinson. It’s a four-billion-year-old mystery waiting to be solved.

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