Our neighboring planet, Venus, is an oddity in many ways. For starters, it rotates in the opposite direction to most other planets, including Earth, so on Venus the sun rises in the west.

Furthermore, on the planet Venus, a day lasts just over 243 Earth days, which actually makes it longer than a Venusian year, which is only about 224 Earth days.

Many scientists believe that the long days are the result of the sun’s strong pull on the planet.

Mercury, which is even closer to Earth, also has fairly long days: three every two Mercurian years.

But scientists are still puzzled by Venus’ retrograde, or reverse, rotation. Now, a team of scientists from the French research institute Astronomie et Systemes Dynamiques has proposed a new explanation, published in the journal Nature.

The planet Venus is an oddity in many ways

The current theory holds that Venus originally rotated in the same direction as most of the other planets, and in a sense still does.

So it simply reversed its axis 180 degrees at a time. In other words, it spins in the same direction it always has, only it rotates upside down, so that if we look at it from other planets, the rotation appears to be reversed.

Scientists have argued that the Sun’s gravitational pull on the planet’s very dense atmosphere could have caused strong atmospheric tides.

Such tides, combined with friction between Venus’ mantle and core, could have caused the reversal in the first place.

Venus would have originally rotated in the same direction as most of the other planets

Now, Alexandre Correira and Jacques Laskar suggest that Venus may not have flipped at all, they write Scientific American.

The researchers instead propose that its rotation slowed to a standstill and then reversed direction. Taking into account the factors mentioned above, as well as the effects of tides on other planets, the team concluded that the axis of Venus could have moved to a variety of positions throughout the planet’s evolution.

Whether it has flipped or not, it is bound to settle into one of four stable rotational states – two in either direction.

The researchers add that Venus would be more stable in one of two states of retrograde rotation. So, essentially, it was only a matter of time before Venus started rotating in the opposite direction.

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