Strong ‘electric wind’ on Venus removed the components of water from its upper atmosphere, which may have played a significant role in stripping the planet of its oceans, a new study has found.
Scientists at NASA and University College London (UCL) discovered that Venus’ electric field is so strong that it can accelerate the heavy electrically charged component of water – oxygen – to speeds fast enough to escape the planet’s gravity.
“We never dreamt an electric wind could be so powerful that it can suck oxygen right out of an atmosphere into space,” said Glyn Collinson, a scientist at NASA’s Goddard Space Flight Centre.
“This is something that definitely has to be on the checklist when we go looking for habitable planets around other stars,” Collinson, who was previously at UCL.
When water molecules rise into the upper atmosphere, sunlight breaks the water into hydrogen ions which are fast and escape easily, and heavier oxygen ions which are carried away by the electric field.
“We’ve been studying the electrons flowing away from Titan and Mars as well as from Venus, and the ions they drag away to space to be lost forever,” said Andrew Coates from UCL.
“We found that over 100 metric tonnes per year escapes from Venus by this mechanism – significant over billions of years,” said Coates.
“The new result here is that the electric field powering this escape is surprisingly strong at Venus compared to the other objects,” he said.
Venus is the planet most like Earth in terms of its size and gravity, and evidence suggests it once had oceans worth of water which boiled away to steam long ago with surface temperatures of around 460 degrees Celsius.
Yet Venus’ thick atmosphere, about 100 times the pressure of Earth’s, has 10,000 to 100,000 times less water than our atmosphere, suggesting something removed all the steam.
Scientists thought it was the solar wind eroding the remainder of an ocean’s worth of oxygen and water slowly from Venus’ upper atmosphere, but the new findings suggest it was an aggressive electric wind instead.
When monitoring electrons flowing out of the upper atmosphere, researchers noticed the electrons were not escaping at their expected speeds because they were being tugged on by Venus’ potent electric field.
By measuring the change in speed, the team found the strength of the field to be much stronger than expected, and at least five times more powerful than at Earth.
Understanding the role played by planet’s electric winds will help astronomers improve estimates of the size and location of habitable zones around other stars.
The study was published in the journal Geophysical Research Letters.