Although you could bake a pizza on its surface today, popular thinking is that Venus was once cool enough to hold water on its surface. Of course, as the planet heated, that water turned to vapor and should now be trapped in the planet's dense atmosphere – but it's not. So where did the water go? According to new research, the likely culprit is likely a super-strong "electric wind" that blows off the surface of Venus carrying ions with it into space.
When the Venusian water turned to steam and rose to the upper atmosphere, it would have been broken into its constituent parts – hydrogen and oxygen – by sunlight. Hydrogen is fast and light, so it easily escaped the planet's gravity. But oxygen is slower and heavier, and would have needed a boost to vanish. Thanks to data gathered by the the electron spectrometer aboard the ESA's Venus Express, the new study points to the electric wind as the culprit.
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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," says Glyn Collinson, a scientist at NASA's Goddard Space Flight Center. "You and all your ion friends will be dragged off kicking and screaming into space by an invisible hand, and nothing can save you."
While it's been suspected that all planets with atmospheres have an electric field, the strength of that field and how fast the particles were shooting off Venus was a surprise to the researchers. The spectrometer found that the speed of the planet's electric wind was five times that of Earth's, although they don't quite know why it's so much more powerful.
"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."
Previous theories about where the leftover oxygen from Venus' water went included the thought that it had oxidized the planet's rocks over the years, or that it had been carried away by the solar wind streaming off our Sun. But the new study, published today in the journal Geophysical Research Letters, says that the electric wind would have been strong enough to do the job on its own.
"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," says Collinson.
The discovery could help astronomers better understand the solar wind on other planets, says NASA. For example, the space organization is currently searching for an electric wind on Mars using the MAVEN spacecraft that's been orbiting the Red Planet since September 2014.
"MAVEN is a robotic detective on this four-billion-year-old mystery of where the atmosphere and oceans went, and the electric wind has long been a prime suspect," Collinson says.
If you think Collinson has a way with words, you're not mistaken, as you'll see in this video where he summarizes the new findings.