The mystery of why Venus spins 鈥渂ackwards鈥� may have been solved. French astronomers have shown that, in fact, it is the planet鈥檚 most natural state.
Venus rotates from east to west. All the other planets in our solar system spin from west to east, except Uranus which is tipped on its side. The only way to explain this had been to assume Venus formed with an unnaturally large tilt that caused the planet to turn upside-down.
But Alexandre Correla and Jacques Laskar, at Astronomie et Systemes Dynamiques, Paris, went back to basics to look at the problem. 鈥淲e looked at the critical points in the equations like a mathematician would do,鈥� says Laskar.
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They found there was no need for the initial tilt. Better computational power allowed them to fully account for the various forces at work on Venus, such as friction between the planet鈥檚 core and mantle, the heating of the dense atmosphere by the Sun and the tidal effect of the Sun鈥檚 gravitational field on the atmosphere.
Laskar found that these could up-end the planet from almost any initial configuration.
Stop and start
The true surprise, however, was that Venus may not have tipped over at all.
Instead, the atmosphere may simply have slowed the planet down and then started it spinning the other way. This insidious process is the unique result of the thick atmosphere always lagging behind as the planet rotates.
鈥淰enus鈥� present observable situation could be reached by either of the two completely different scenarios,鈥� Laskar told 快猫短视频. Whilst it is impossible to know which route Venus took, Laskar computed that it was almost inevitable that Venus would have ended up this way.
If true, Venus-like extrasolar planets might also be expected to exhibit the same backward rotation. 鈥淚t is a general result and will apply to any planet with a heavy atmosphere,鈥� confirms Laskar.
More at: Nature (vol 411, p 767)