Electric field at Venus
ESA's Venus Express has detected a surprisingly strong electric field at Venus – the first time this has been measured at any planet. With a potential of around 10 V, this is up to five times larger than scientists expected and it is sufficient to deplete Venus' upper atmosphere of oxygen, one of the components of water.
Unlike Earth, Venus has no significant magnetic field of its own to protect the planet from the solar wind, a powerful stream of charged particles blowing from the Sun. When the magnetic field carried by the solar wind encounters Venus, it drapes around the planet's ionosphere (shown here in orange), drawing its particles away.
While protons and other ions (shown in blue in the inset) feel a pull due to the planet's gravity, electrons (shown in red in the inset) are much lighter and thus able to escape the gravitational tug more easily.
As the negative electrons drift upwards in the atmosphere and away into space, they are nevertheless still connected to the positive protons and ions via the electromagnetic force, and this results in an overall vertical electric field being created above the planet's atmosphere.
Venus Express has detected the electric field at Venus behind the terminator line, which divides the planet's day and night sides.