Magnetic field measurements at Venus

This figure is based on data from the magnetometer (MAG) on board ESA’s Venus Express. MAG has allowed the clear determination of the
position of Venus’ bow shock – the boundary region which separates the undisturbed solar wind from the solar wind affected by the planet’s
presence. This is a very sharp boundary, and is present at all planets.

After having encountered the bow shock, the solar wind flows around the planet. Then, due to interaction with the ionised upper atmosphere, it is
deviated. The location of the bow shock is expected to be where there is a complete deflection of the solar wind by the magnetised ionosphere (upper
atmospheric layer).

Before Venus Express, we had no knowledge of whether or not solar wind would reach the atmosphere when solar activity is at maximum in its 11-
year cycle. MAG measurements showed that it almost entirely deviated and little or no solar wind enters Venus’ atmosphere even at solar maximum.
So, the atmosphere is shielded by the magnetic field induced by the solar wind itself.

The high-resolution magnetic field data from MAG has also allowed the identification of the outer boundary of the magnetosphere induced by the
interaction with the solar wind: a ‘magnetopause’ that deflects and stops the solar wind.