Seen from Earth, Venus is a soft yellow-orange, a bright planet that is known as the morning star. But up close -- watch out! Its atmosphere is hellish with average temperatures hot enough to melt lead and rain showers of sulphuric acid. Now, a new paper reveals it’s even worse than that. Writing in the journal Geophysical Research Letters, researchers at NASA’s Goddard Space Flight Center say there is an “electric wind” on the second planet from the sun that may have stripped Venus of its oceans. “It’s amazing, shocking,” said NASA scientist Glyn Collinson. “We never dreamt an electric wind could be so powerful that it can suck oxygen right out of an atmosphere into space. This is something that has to be on the checklist when we go looking for habitable planets around other stars.”
Sister planets, but not twins
Venus’s size and gravity are similar to Earth’s, so it's often thought of as Earth's sister planet. It is believed that like Earth, Venus once had oceans, but those boiled away in temperatures that can reach 460 Celsius. But while the atmosphere is very thick - about 100 times the pressure of Earth - there is relatively little water vapor in the air. Now researchers think Venus’ electric wind may have blasted water particles into hydrogen and oxygen ions, which later escaped from the atmosphere altogether. “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,” Collinson said. Any water left by the electric wind would likely have been finished up by the solar wind, researchers said.
This June 2004 photo shows the transit of Venus, which occurs when Venus passes between the Earth and the sun.
Researchers believe any planet with an atmosphere is surrounded by a weak electrical field, but Venus’ is much stronger than, say, Earth’s. On Earth, the electric field is less than 2 volts, while on Venus, it’s 10 volts. “We don’t really know why it is so much stronger at Venus than Earth,” Collinson said, “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.”
The stronger field helps push hydrogen and oxygen molecules upward and eventually out of the atmosphere. “If you were unfortunate enough to be an oxygen ion in the upper atmosphere of Venus, then you have won a terrible, terrible lottery,” Collinson said. “You and all your ion friends will be dragged off kicking and screaming into space by an invisible hand, and nothing can save you.” The researchers add that electric wind may have also played a role on Mars, which is also believed to have once had much more water than today. “We are actively hunting for Mars’ electric wind with MAVEN’s full arsenal of scientific instruments,” Collinson said. “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.”