On 15 May 2006, Venus Express was crossing the Venusian magnetotail when it observed a rotational magnetic field structure over a period of about 3 minutes. Calculations based on its duration and speed imply that it was about 3400 km across.
Magnetic reconnection in Venus' induced magnetotail
The event, which took place about 1.5 Venus radii (about 9000 km) down the magnetotail, is thought to be evidence of a passing plasmoid - a transient magnetic loop structure which is formed by magnetic reconnection in a planetary magnetotail.
The animation shows how reconnection splits the induced magnetotail of Venus, causing most of the plasma in the tail to be ejected into space. It also forms a plasmoid structure - the closed loop - which heads towards the planet and channels a fraction of the energy flux of the solar wind into the night-side atmosphere.
The animation is not to scale.