Venus's Deadly Electric Wind May Have Made It Uninhabitable
Venus has long been considered Earth's "twin," since it's only slightly smaller and closer to the sun than our own planet. Planetary researchers even think that Venus was a host to large amounts of water 4 billion years ago, meaning that there might have been potential lifeforms on the planet. Unfortunately, as it heated up, much of this water evaporated into the atmosphere, where it's molecules were split apart by the sunlight and lost into space.
Today, the Venusian atmosphere is quite different from Earth's, consisting mostly of carbon dioxide, with a runaway greenhouse effect and surface temperatures of around 860 degrees Fahrenheit. But it doesn't stop there; an international team of scientists has just discovered a key difference between Venus and Earth - Venus has an electric field of around 10 volts which is at least five times higher than expected.
"We think all planets with atmospheres have a weak electric field, but this is the first time we have actually been able to detect one," team member Dr. Glyn Collinson from NASA's Goddard Space Flight Center said in an ESA statement. According to Dr. Collinson, the Venusian electric field is so strong that it can accelerate oxygen - the main component of water - to speeds fast enough to escape the planet's gravity.
When monitoring electrons flowing out of the upper atmosphere, the team noticed the electrons were not escaping at their expected speeds. By measuring the change in speed using the NASA SwRI-UCL electron spectrometer on ESA's Venus spacecraft, the team found the strength of Venus's electric field to be much stronger than expected, and at least three to five times more powerful than Earth's.
The strength of the electric field is important in the process by which water molecules break apart and are lost into space. "Even a weak electric wind could still play a role in water and atmospheric loss at any planet. It could act like a conveyer belt, moving ions higher in the ionosphere where other effects from the solar wind could carry them away," said study co-author Dr. Alex Glocer in a statement. When water molecules rise up into the upper atmosphere, sunlight breaks it apart into hydrogen ions and heavier oxygen ions. "We've been studying the electrons flowing away from... Venus, and the ions they drag away to space to be lost forever," said study co-author Prof. Coates. "We found that over 100 metric tons per year escapes from Venus by this mechanism - significant over billions of years."
Another planet on which the electric wind may play an important role is Mars. "With ESA's Mars Express, we have already caught this process in action at Mars, and now NASA's MAVEN spacecraft can now determine its relative importance," said Prof. Coates. "With NASA's Cassini spacecraft, we found that Titan loses 7 metric tons per day this way."
Understanding the role played by a planet's electric winds will help astronomers improve estimates of the size and location of habitable zones around stars. "Water has a key role for life as we know it on Earth and possible elsewhere in the universe," said Dr. Hakan Svedhem, Venus Express project scientist at ESA. "By suggesting a mechanism able to deprive a planet close to its parent star of most of its water, this discovery calls for a rethink of how we define a habitable planet, not only in our Solar System, but also in the context of exoplanets."