When Pioneer Venus visited our sister planet in 1979, it found an atmospheric feature called a "dipole" near Venus' north pole -- a pair of eddies swirling and rotating around each other as Venus rotated. When ESA's Venus Express arrived in 2006, it observed the same sort of thing at Venus' south pole, and scientists wrote a lot about how Venus was symmetric from north to south and how the polar dipoles were atmospheric features that were stable over decades.
...it turns out it's not stable! Venus Express has been there for more than four years now, and as it's kept watching Venus' swirling atmospheric patterns, that "stable" southern dipole turned out not to be stable. At all. In a press release issued today, Venus scientist Giuseppi Piccioni remarks that the original observation of the southern dipole by Venus Express was "just a coincidence...the dipole in reality is not a stable feature on Venus, but just one shape among others."
via Venus: Not so neat and tidy as we thought - The Planetary Society Blog | The Planetary Society.
Don't fall in.