As all planets in the solar system, Venus is hit by the solar wind, a million miles-per-hour stream of charged particles coming from the Sun. Our Earth is protected from this continuous solar bombardment by its magnetic field, which deflects the charged particles around the planet, leaving an intact and therefore habitable atmosphere.
Venus however, has no magnetic field, so the solar wind impacts directly on the outer atmospheric layers. From previous space missions, it is known that during times of strong magnetic activity in the 11-years solar cycle, a strong barrier builds up in the Venus ionosphere and withstands access of the solar wind to the atmosphere.
For times of low solar activity, details of the interaction are less well understood.
Now for the Venus Express mission solar minimum conditions prevail, offering an excellent opportunity for further study. The analysis of the magnetometer data of VEXMAG proves the development of a strong enough magnetic shield in the ionosphere, preventing the solar wind from entering the atmosphere also at solar minimum.
Therefore, we can say that the Venus ionosphere is able to build up an efficient barrier to the solar wind for all regimes of solar wind activity.
- Figure: Magnetometer data for a typical flight across the different plasma layers around Venus :
A: Venus-bow shock in the on-streaming solar wind;
B: Inner boundary of the induced magnetic barrier.
C: In the Venus ionosphere, at closest approach to the planetary surface (250 km).