Venus is one of the most Earth-like planets in our solar system in terms of its size and gravity. However, with surface temperatures at around 860 degrees Fahrenheit, any oceans would have boiled away to steam making Venus uninhabitable today.
Astronomers now believe much of this early steam was stripped away; the light hydrogen escaped, while the oxygen oxidised rocks over billions of years. Also a solar wind – a million-mile-per-hour stream of electrically conducting gas blowing from the Sun – could have slowly eroded the remainder of an ocean’s worth of oxygen and water from Venus’ upper atmosphere.
“It’s amazing, shocking,” said Glyn Collinson, a scientist at Nasa’s Goddard Space Flight Center, Greenbelt, Maryland. “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.”
Collinson is lead author of a paper about this research published today in Geophysical Research Letters, a journal of the American Geophysical Union.
“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 added. “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 team discovered Venus’ electric field using the electron spectrometer, part of the ASPERA-4 instrument on the Esa Venus Express. By monitoring electrons flowing out of the upper atmosphere, it noticed these electrons were not escaping at expected speeds. By measuring the change in speed, the team was able to measure the strength of the field, finding it to be much stronger than anyone had expected – at least five times more powerful than on Earth.