At http://phys.org/print275843816.html … NASAs Pioneer Venus orbiter, as long ago as 1978, suggested the ionosphere of Venus had a magnetised state with a large horizontal magnetic field but at other times it was, apparently, unmagnetised with no obvious large magnetic field. Instead, it is thought, or was, it had numerous small magnetic structures known as flux ropes and it was the polar wind, or Venus facing sun spot eruptions, that caused it to have an obvious magnetic state.
Recent observations from EPAs Venus Express (in 2008 and 2009) are now being used in reports that the small flux ropes can become giant flux ropes – which form surprisingly often. In addition, large flux ropes have been observed in the magnetotail of Venus. How the flux ropes form is a mystery.